[PATCH v2 00/10] liveupdate: Preserve tmpfs files across Live Update

[PATCH v2 00/10] liveupdate: Preserve tmpfs files across Live Update

[David Matlack]

This series can be found on GitHub:

  https://github.com/dmatlack/linux/tree/liveupdate/tmpfs/v2

This series allows userspace to preserve files on tmpfs mounts across a
Live Update, in addition to memfds. Today the memfd file handler only
accepts unlinked shmem files, and LIVEUPDATE_SESSION_RETRIEVE_FD always
restores them as anonymous memfds. Userspace therefore has to put every
in-memory file it wants to preserve in a memfd, which works for VM guest
memory but not for other files that live on tmpfs mounts, such as
in-memory logs, binaries, and configuration files.

The kernel preserves the contents, size, file position and seals of each
file. After the Live Update, userspace retrieves each file onto a tmpfs
mount of its choice and links it at the path of its choice, so userspace
decides the directory structure, names, owners and permissions of the
restored files.

This series builds on the per-file-handler argument for
LIVEUPDATE_SESSION_PRESERVE_FD and LIVEUPDATE_SESSION_RETRIEVE_FD from
Pasha's v1 [1], following Pratyush's suggestion on the RFC [2], and on
the design discussion on Pasha's v1 [3].

[1] https://lore.kernel.org/kexec/20261015093816.2438942-1-pasha.tatashin@soleen.com/
[2] https://lore.kernel.org/kexec/2vxz7bjmkjeu.fsf@kernel.org/
[3] https://lore.kernel.org/kexec/atE53vmlDeA4cWD2@google.com/

Series Overview
---------------

This series implements the following:

  1. Let userspace pass a file-handler-specific argument to
     LIVEUPDATE_SESSION_PRESERVE_FD and LIVEUPDATE_SESSION_RETRIEVE_FD,
     and let file handlers mark retrieve failures as retryable, so that
     userspace can fix a bad argument and try again without losing the
     preserved file (patches 1-3).

  2. Rename the memfd file handler (memfd_luo) to shmem_luo, since it
     preserves shmem files, which will include files on tmpfs mounts.
     Preserving memfds created with MFD_HUGETLB will need a separate
     handler, so naming the handler after the filesystem avoids another
     rename later. The compatible string stays "memfd-v2" (patch 4).

  3. Fix two existing problems in the retrieve path: a WARN_ON() that
     userspace can trigger when tracking a retrieved file fails, and a
     leak of the preserved folios when a retrieve fails before it
     restores them (patches 5-6).

  4. Retrieve files that were preserved from a tmpfs mount onto a tmpfs
     mount chosen by userspace, via the new struct
     liveupdate_shmem_retrieve_arg. The kernel creates the file as if by
     openat(dirfd, ".", O_TMPFILE | flags, mode), so the file gets the
     same flags, owner, permission checks and security labels as any
     other new file in that directory, and is charged to that mount.
     The kernel fills the file before returning it, so nothing else can
     access the file before it is complete, and userspace links it at
     the path it wants with linkat() (patch 7).

  5. Allow preserving tmpfs files that are still linked, and require
     permission to change the size of a file to preserve it, since
     preserving a file freezes its size for all users of the file
     (patch 8).

  6. Allow retrieving tmpfs files with O_RDONLY so that restored
     binaries can be executed before the session is finished (patch 9).

  7. Add a kexec selftest for preserving and retrieving tmpfs files
     (patch 10).

uAPI Changes
------------

  - struct liveupdate_session_preserve_fd and struct
    liveupdate_session_retrieve_fd gain a 64-bit @arg field, a pointer
    to a handler-specific argument that starts with a 32-bit size
    field. Callers that pass the old struct size are not affected.

  - Passing a non-zero @arg when retrieving a token that was already
    retrieved fails with -EBUSY instead of silently ignoring @arg.

  - New struct liveupdate_shmem_retrieve_arg, with @dirfd, @flags and
    @mode, for retrieving tmpfs files. Files that were preserved from a
    tmpfs mount can only be retrieved with it, and memfds can only be
    retrieved without it. Unlinked tmpfs files (e.g. created with
    O_TMPFILE) were retrieved as memfds before this series, and now
    require the argument too.

  - Preserving a file now requires permission to change its size (see
    Open Questions).

ABI Changes
-----------

  - struct shmem_luo_ser (formerly struct memfd_luo_ser) gains a
    SHMEM_LUO_FLAG_TMPFS flag in its existing @flags field, which
    records that a file was on a tmpfs mount rather than the internal
    shmem mount that memfds use.

Open Questions
--------------

  - Preserving a file freezes its size until it is unpreserved: For all
    users of the file, truncating it, fallocate() and writes past its
    end fail with -EPERM, and the owner of the file can't undo that.
    Linked files can be reached by anyone who can read them, so without
    a permission check, anyone with a session fd could preserve e.g. a
    world-readable file in /dev/shm through a read-only fd and break its
    owner. Patch 8 therefore requires permission to write to the file
    (inode_permission(MAY_WRITE), but neither a file opened for writing
    nor a writable mount), or ownership if the file is immutable or on a
    read-only superblock, since its size can't change anyway. The check
    applies to all files, including memfds, where it passes in practice
    since memfds are created with mode 0777 (or 0666). Is this the right
    permission model for preserving files? Should this apply all files
    or just shmem files?

  - Is patch 9 (retrieving tmpfs files with O_RDONLY) worth merging?
    Without it, userspace can only retrieve files O_RDWR or O_WRONLY
    which then LUO keeps open until the session is finished, so
    executing a restored binary fails with -ETXTBSY until then.
    Supporting O_RDONLY retrieve is fairly simple so I think it is worth
    supporting.

Merge Plan
----------

This series applies on top of the next branch of liveupdate.git
(commit 80cf37169dae ("Merge branch 'kho-bootmem' into next")) and is
targeting Linux 7.5.

The series will be merged through liveupdate.git.

[4] https://lore.kernel.org/kexec/20261020144710.4154339-1-pasha.tatashin@soleen.com/

Testing
-------

All patches were build-tested individually. The series was tested on
x86_64 and arm64 in QEMU using the Live Update selftests:

  - luo_tmpfs (new): 31 test cases covering the contents, size,
    position, seals and holes of restored files; creating the file like
    open(O_TMPFILE), with the requested flags and mode, the caller as
    owner, and O_EXCL; executing restored binaries before and after the
    session is finished; preserving files through read-only fds, on
    read-only mounts and superblocks, and immutable files; rejecting
    files that the caller can't write to; block accounting on the target
    mount, including large folios that extend past the end of the file;
    mount and memcg limits; memfds; invalid arguments; retrieving a
    token twice; and that no kernel warnings are triggered.

    The main downside of this new test is that it is large (2k lines).
    It was trivial to generate with AI, but can understand if it is too
    large to review. I can look for ways to simplify it. On the other
    hand, having comprehensive test cases is quite nice.

  - luo_kexec_simple, luo_multi_session, luo_stress_files and
    luo_stress_sessions.

  - liveupdate (including the new preserve_memfd_with_arg test).

The selftests were run with vmtest.sh:

  $ tools/testing/selftests/liveupdate/vmtest.sh -T luo_tmpfs

Changelog
---------

v2:
 - Rebase onto liveupdate/next.
 - Drop the LIVEUPDATE_SESSION_FREEZE patches, which Pasha posted
   separately [4], and the session freeze tests from patch 2.
 - Patch 1: Fail with -EBUSY if an argument is passed for a token that
   was already retrieved. Drop liveupdate_claim_file() and
   liveupdate_unclaim_file(), which nothing uses anymore.
 - Rename memfd_luo to shmem_luo, and clarify in the documentation that
   memfd means a memfd created without MFD_HUGETLB (Pratyush).
 - Don't WARN if tracking a retrieved file fails (Sashiko).
 - Don't make early retrieve failures permanent, which also fixes
   leaking the preserved folios when they happen (Sashiko).
 - Create the restored tmpfs file in a directory chosen by userspace,
   like open(O_TMPFILE), instead of restoring it into an existing file
   provided by userspace (Pasha). This removes the need to check the
   provided file, and ensures that nothing else can access the file
   before it is complete. Don't preserve the name of the file, which
   userspace already knows, so that it stays out of the ABI.
 - Pass the flags from userspace through to file_open_root(), and only
   reject unknown flags, unknown mode bits and O_PATH, like openat2().
 - Decide whether a file is a tmpfs file by its superblock instead of
   its link count, so that unlinked tmpfs files stay on a tmpfs mount
   (Pasha).
 - Require permission to change the size of a file to preserve it
   (Sashiko).
 - Split O_RDONLY support for retrieved tmpfs files into its own patch
   so we can decide if it's worth merging (Pratyush).
 - Replace the selftest changes with a dedicated kexec selftest.

v1: https://lore.kernel.org/kexec/20261015093816.2438942-1-pasha.tatashin@soleen.com/
rfc: https://lore.kernel.org/kexec/20260901180713.4185641-1-dmatlack@google.com/


David Matlack (7):
  mm: Rename memfd_luo to shmem_luo
  liveupdate: Don't WARN if tracking a retrieved file fails
  mm/shmem_luo: Don't make early retrieve failures permanent
  mm/shmem_luo: Retrieve tmpfs files onto a tmpfs mount chosen by
    userspace
  mm/shmem_luo: Allow preserving tmpfs files that are still linked
  mm/shmem_luo: Allow retrieving tmpfs files with O_RDONLY
  selftests/liveupdate: Add a test for preserving tmpfs files

Pasha Tatashin (3):
  liveupdate: Pass user argument to file preserve and retrieve
  selftests: liveupdate: Add tests for preserve and retrieve user
    argument
  liveupdate: Allow file handlers to mark retrieve failures as retryable

 Documentation/core-api/liveupdate.rst         |    2 +-
 Documentation/mm/index.rst                    |    2 +-
 Documentation/mm/memfd_preservation.rst       |   23 -
 Documentation/mm/shmem_preservation.rst       |   23 +
 MAINTAINERS                                   |    4 +-
 include/linux/kho/abi/{memfd.h => shmem.h}    |   56 +-
 include/linux/liveupdate.h                    |   55 +-
 include/uapi/linux/liveupdate.h               |   52 +-
 kernel/liveupdate/Kconfig                     |    8 +-
 kernel/liveupdate/luo_file.c                  |  110 +-
 kernel/liveupdate/luo_internal.h              |    5 +-
 kernel/liveupdate/luo_session.c               |    6 +-
 mm/Makefile                                   |    2 +-
 mm/internal.h                                 |    1 +
 mm/shmem.c                                    |    9 +
 mm/{memfd_luo.c => shmem_luo.c}               |  369 ++-
 tools/testing/selftests/liveupdate/Makefile   |    1 +
 tools/testing/selftests/liveupdate/config     |    4 +
 .../liveupdate/lib/include/libliveupdate.h    |    3 +
 .../selftests/liveupdate/lib/lu_utils.c       |   17 +-
 .../testing/selftests/liveupdate/liveupdate.c |   44 +
 .../testing/selftests/liveupdate/luo_tmpfs.c  | 2000 +++++++++++++++++
 .../selftests/liveupdate/run-vmtests.sh       |    1 +
 23 files changed, 2630 insertions(+), 167 deletions(-)
 delete mode 100644 Documentation/mm/memfd_preservation.rst
 create mode 100644 Documentation/mm/shmem_preservation.rst
 rename include/linux/kho/abi/{memfd.h => shmem.h} (54%)
 rename mm/{memfd_luo.c => shmem_luo.c} (50%)
 create mode 100644 tools/testing/selftests/liveupdate/luo_tmpfs.c


base-commit: 80cf37169daef112b6bea9ae7d9808355a045475
-- 
2.56.0.257.gf7497c7d27-goog

[PATCH v2 01/10] liveupdate: Pass user argument to file preserve and retrieve

[David Matlack]

From: Pasha Tatashin <pasha.tatashin@soleen.com>

Allow userspace to pass a file-handler-specific argument structure when
preserving or retrieving an FD via LUO. File handlers may need
additional context during preservation or retrieval, such as a target
FD, device location, or handler-specific parameters, without introducing
separate ioctls for each file type. Whether the argument is required,
optional, or unused is defined by the file handler.

Extend struct liveupdate_session_preserve_fd and
struct liveupdate_session_retrieve_fd with a 64-bit arg field pointing
to a handler-defined argument structure that begins with a 32-bit size
field. Because IOCTL_OP validates a minimum size up to the token field,
existing callers passing the 16-byte struct remain compatible and have
arg zero-filled by copy_struct_from_user().

Add parg and rarg (struct liveupdate_arg_spec) to
struct liveupdate_file_ops, initialized via LIVEUPDATE_ARG(_struct,
_min_last), which records the full struct size and minimum required size
while enforcing at compile time that handler argument structures begin
with a 32-bit size field. When arg is non-zero, LUO validates the
minimum size and copies the user argument via copy_struct_from_user() up
to the handler's expected size and passes the kernel copy in
struct liveupdate_file_op_args, or returns -EOPNOTSUPP if the handler
does not accept an argument.

The argument only applies to the retrieve that restores the file.
Retrieving a token that was already retrieved returns the existing file,
so fail with -EBUSY if a non-zero argument is passed then, instead of
silently ignoring it.

Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: David Matlack <dmatlack@google.com>
---
 include/linux/liveupdate.h       | 44 +++++++++++++++++++
 include/uapi/linux/liveupdate.h  | 10 +++++
 kernel/liveupdate/luo_file.c     | 73 +++++++++++++++++++++++++++++---
 kernel/liveupdate/luo_internal.h |  5 ++-
 kernel/liveupdate/luo_session.c  |  6 ++-
 5 files changed, 128 insertions(+), 10 deletions(-)

diff --git a/include/linux/liveupdate.h b/include/linux/liveupdate.h
index 6051abc0612c..7543f5d648d3 100644
--- a/include/linux/liveupdate.h
+++ b/include/linux/liveupdate.h
@@ -22,6 +22,36 @@ struct liveupdate_flb;
 struct liveupdate_session;
 struct file;
 
+/**
+ * struct liveupdate_arg_spec - Specification of a file handler user argument.
+ * @size:     Full size of the argument structure in the current kernel.
+ * @min_size: Minimum valid user-supplied size (offsetofend of the last
+ *            required field).
+ */
+struct liveupdate_arg_spec {
+	size_t size;
+	size_t min_size;
+};
+
+/**
+ * LIVEUPDATE_ARG - Validated specification of a file handler argument struct.
+ * @_struct:   The argument structure type.
+ * @_min_last: The last required member in @_struct.
+ *
+ * All file handler argument structures passed via
+ * &liveupdate_session_preserve_fd.arg or &liveupdate_session_retrieve_fd.arg
+ * must begin with a 32-bit @size field so they can be extended compatibly.
+ * Use this macro to initialize &liveupdate_file_ops.parg and
+ * &liveupdate_file_ops.rarg.
+ */
+#define LIVEUPDATE_ARG(_struct, _min_last)				\
+	{								\
+		.size = sizeof(_struct) +				\
+			BUILD_BUG_ON_ZERO(offsetof(_struct, size) != 0) + \
+			BUILD_BUG_ON_ZERO(sizeof_field(_struct, size) != sizeof(u32)), \
+		.min_size = offsetofend(_struct, _min_last),		\
+	}
+
 /**
  * struct liveupdate_file_op_args - Arguments for file operation callbacks.
  * @handler:          The file handler being called.
@@ -40,6 +70,11 @@ struct file;
  *                    is not preserved. Set by the handler's .preserve()
  *                    callback, and must be freed in the handler's
  *                    .unpreserve() callback.
+ * @arg:              Kernel copy of the user-provided argument for .preserve()
+ *                    and .retrieve(), or %NULL if none was provided. Allocated
+ *                    to the handler's expected argument size with any trailing
+ *                    bytes beyond the user-supplied size zero-filled. Valid
+ *                    only for the duration of the callback.
  *
  * This structure bundles all parameters for the file operation callbacks.
  * The 'data' and 'file' fields are used for both input and output.
@@ -51,6 +86,7 @@ struct liveupdate_file_op_args {
 	struct file *file;
 	u64 serialized_data;
 	void *private_data;
+	const void *arg;
 };
 
 /**
@@ -68,6 +104,12 @@ struct liveupdate_file_op_args {
  *                resources in the session.
  * @finish:       Required. Final cleanup in the new kernel.
  * @get_id:       Optional. Returns a unique identifier for the file.
+ * @parg:         Optional. Specification of the user argument structure
+ *                accepted by @preserve, initialized via LIVEUPDATE_ARG(). If
+ *                unset, non-zero user arguments are rejected with -EOPNOTSUPP.
+ * @rarg:         Optional. Specification of the user argument structure
+ *                accepted by @retrieve, initialized via LIVEUPDATE_ARG(). If
+ *                unset, non-zero user arguments are rejected with -EOPNOTSUPP.
  * @owner:        Module reference
  *
  * All operations (except can_preserve) receive a pointer to a
@@ -84,6 +126,8 @@ struct liveupdate_file_ops {
 	bool (*can_finish)(struct liveupdate_file_op_args *args);
 	void (*finish)(struct liveupdate_file_op_args *args);
 	unsigned long (*get_id)(struct file *file);
+	struct liveupdate_arg_spec parg;
+	struct liveupdate_arg_spec rarg;
 	struct module *owner;
 };
 
diff --git a/include/uapi/linux/liveupdate.h b/include/uapi/linux/liveupdate.h
index 4043d4038712..e806752c2fc6 100644
--- a/include/uapi/linux/liveupdate.h
+++ b/include/uapi/linux/liveupdate.h
@@ -126,6 +126,8 @@ struct liveupdate_ioctl_retrieve_session {
  * @size:  Input; sizeof(struct liveupdate_session_preserve_fd)
  * @fd:    Input; The user-space file descriptor to be preserved.
  * @token: Input; An opaque, unique token for preserved resource.
+ * @arg:   Input; User-space pointer to a file-handler-specific argument
+ *         structure starting with a 32-bit size field, or 0 if unused.
  *
  * Holds parameters for preserving a file descriptor.
  *
@@ -149,6 +151,7 @@ struct liveupdate_session_preserve_fd {
 	__u32		size;
 	__s32		fd;
 	__aligned_u64	token;
+	__aligned_u64	arg;
 };
 
 #define LIVEUPDATE_SESSION_PRESERVE_FD					\
@@ -160,6 +163,8 @@ struct liveupdate_session_preserve_fd {
  * @fd:    Output; The new file descriptor representing the fully restored
  *         kernel resource.
  * @token: Input; An opaque, token that was used to preserve the resource.
+ * @arg:   Input; User-space pointer to a file-handler-specific argument
+ *         structure starting with a 32-bit size field, or 0 if unused.
  *
  * Retrieve a previously preserved file descriptor.
  *
@@ -173,12 +178,17 @@ struct liveupdate_session_preserve_fd {
  * attempts to retrieve the token fail with the same error code. Failed
  * retrieves are not retried.
  *
+ * Retrieving a token that was already retrieved successfully returns a new file
+ * descriptor for the same file. The @arg only applies to the retrieve that
+ * restores the file, so passing a non-zero @arg then fails with -EBUSY.
+ *
  * Return: 0 on success, negative error code on failure (e.g., invalid token).
  */
 struct liveupdate_session_retrieve_fd {
 	__u32		size;
 	__s32		fd;
 	__aligned_u64	token;
+	__aligned_u64	arg;
 };
 
 #define LIVEUPDATE_SESSION_RETRIEVE_FD					\
diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index a39992da504f..eeeb3b5ff2fa 100644
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -126,6 +126,7 @@
 #include <linux/xarray.h>
 #include <linux/slab.h>
 #include <linux/string.h>
+#include <linux/uaccess.h>
 #include "luo_internal.h"
 
 static LIST_HEAD(luo_file_handler_list);
@@ -202,11 +203,45 @@ static bool luo_token_is_used(struct luo_file_set *file_set, u64 token)
 	return false;
 }
 
+static int luo_copy_user_arg(u64 user_arg, const void **argp,
+			     const struct liveupdate_arg_spec *spec)
+{
+	void *karg __free(kfree) = NULL;
+	void __user *uptr;
+	u32 user_size;
+	int err;
+
+	if (!user_arg)
+		return 0;
+	if (!spec->size)
+		return -EOPNOTSUPP;
+
+	uptr = u64_to_user_ptr(user_arg);
+	if (get_user(user_size, (u32 __user *)uptr))
+		return -EFAULT;
+	if (user_size < spec->min_size)
+		return -EINVAL;
+	if (user_size > PAGE_SIZE)
+		return -E2BIG;
+
+	karg = kmalloc(spec->size, GFP_KERNEL);
+	if (!karg)
+		return -ENOMEM;
+
+	err = copy_struct_from_user(karg, spec->size, uptr, user_size);
+	if (err)
+		return err;
+
+	*argp = no_free_ptr(karg);
+	return 0;
+}
+
 /**
  * luo_preserve_file - Initiate the preservation of a file descriptor.
  * @file_set: The file_set to which the preserved file will be added.
  * @token:    A unique, user-provided identifier for the file.
  * @fd:       The file descriptor to be preserved.
+ * @arg:      User-space pointer to the handler argument structure, or 0.
  *
  * This function orchestrates the first phase of preserving a file. Upon entry,
  * it takes a reference to the 'struct file' via fget(), effectively making LUO
@@ -222,9 +257,11 @@ static bool luo_token_is_used(struct luo_file_set *file_set, u64 token)
  *    (allocates if needed).
  * 3. Iterates through registered handlers, calling can_preserve() to find one
  *    compatible with the given @fd.
- * 4. Calls the handler's .preserve() operation, which saves the file's state
+ * 4. Copies the user argument structure (if @arg is non-zero) according to the
+ *    handler's parg specification.
+ * 5. Calls the handler's .preserve() operation, which saves the file's state
  *    and returns an opaque private data handle.
- * 5. Adds the new instance to the file_set's internal list.
+ * 6. Adds the new instance to the file_set's internal list.
  *
  * On success, LUO takes a reference to the 'struct file' and considers it
  * under its management until it is unpreserved or finished.
@@ -239,10 +276,12 @@ static bool luo_token_is_used(struct luo_file_set *file_set, u64 token)
  *         -EBADF if the file descriptor is invalid.
  *         -ENOSPC if the file_set is full.
  *         -ENOENT if no compatible handler is found.
+ *         -EOPNOTSUPP if @arg is non-zero and the handler does not accept an arg.
  *         -ENOMEM on memory allocation failure.
  *         Other erros might be returned by .preserve().
  */
-int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
+int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd,
+		      u64 arg)
 {
 	struct liveupdate_file_op_args args = {0};
 	struct liveupdate_file_handler *fh;
@@ -278,10 +317,14 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
 	if (err)
 		goto err_fput;
 
+	err = luo_copy_user_arg(arg, &args.arg, &fh->ops->parg);
+	if (err)
+		goto err_module_put;
+
 	err = xa_insert(&luo_preserved_files, luo_get_id(fh, file),
 			file, GFP_KERNEL);
 	if (err)
-		goto err_module_put;
+		goto err_free_arg;
 
 	err = luo_flb_file_preserve(fh);
 	if (err)
@@ -305,6 +348,7 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
 	if (err)
 		goto err_kfree;
 
+	kfree(args.arg);
 	luo_file->serialized_data = args.serialized_data;
 	luo_file->private_data = args.private_data;
 	list_add_tail(&luo_file->list, &file_set->files_list);
@@ -318,6 +362,8 @@ int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd)
 	luo_flb_file_unpreserve(fh);
 err_erase_xa:
 	xa_erase(&luo_preserved_files, luo_get_id(fh, file));
+err_free_arg:
+	kfree(args.arg);
 err_module_put:
 	module_put(fh->ops->owner);
 err_fput:
@@ -547,6 +593,7 @@ void luo_file_unfreeze(struct luo_file_set *file_set,
  * luo_retrieve_file - Restores a preserved file from a file_set by its token.
  * @file_set: The file_set from which to retrieve the file.
  * @token:    The unique token identifying the file to be restored.
+ * @arg:      User-space pointer to the handler argument structure, or 0.
  * @filep:    Output parameter; on success, this is populated with a pointer
  *            to the newly retrieved 'struct file'.
  *
@@ -566,9 +613,11 @@ void luo_file_unfreeze(struct luo_file_set *file_set,
  *          kernel.
  * Return: 0 on success. Returns a negative errno on failure:
  *         -ENOENT if no file with the matching token is found.
+ *         -EOPNOTSUPP if @arg is non-zero and the handler does not accept an arg.
+ *         -EBUSY if @arg is non-zero and the file was already retrieved.
  *         Any error code returned by the handler's .retrieve() op.
  */
-int luo_retrieve_file(struct luo_file_set *file_set, u64 token,
+int luo_retrieve_file(struct luo_file_set *file_set, u64 token, u64 arg,
 		      struct file **filep)
 {
 	struct liveupdate_file_op_args args = {0};
@@ -596,6 +645,13 @@ int luo_retrieve_file(struct luo_file_set *file_set, u64 token,
 	}
 
 	if (luo_file->retrieve_status > 0) {
+		/*
+		 * The argument only applies to the retrieve that restores the
+		 * file. Don't silently ignore it.
+		 */
+		if (arg)
+			return -EBUSY;
+
 		/*
 		 * Someone is asking for this file again, so get a reference
 		 * for them.
@@ -605,10 +661,15 @@ int luo_retrieve_file(struct luo_file_set *file_set, u64 token,
 		return 0;
 	}
 
+	err = luo_copy_user_arg(arg, &args.arg, &luo_file->fh->ops->rarg);
+	if (err)
+		return err;
+
 	args.handler = luo_file->fh;
 	args.session = luo_session_from_file_set(file_set);
 	args.serialized_data = luo_file->serialized_data;
 	err = luo_file->fh->ops->retrieve(&args);
+	kfree(args.arg);
 	if (err) {
 		/* Keep the error code for later use. */
 		luo_file->retrieve_status = err;
@@ -1007,6 +1068,6 @@ int liveupdate_get_file_incoming(struct liveupdate_session *s, u64 token,
 				 struct file **filep)
 {
 	return luo_retrieve_file(luo_file_set_from_session_locked(s),
-				 token, filep);
+				 token, 0, filep);
 }
 EXPORT_SYMBOL_GPL(liveupdate_get_file_incoming);
diff --git a/kernel/liveupdate/luo_internal.h b/kernel/liveupdate/luo_internal.h
index dac6644bfb18..4126b71e9a2e 100644
--- a/kernel/liveupdate/luo_internal.h
+++ b/kernel/liveupdate/luo_internal.h
@@ -101,13 +101,14 @@ int __init luo_session_setup_incoming(u64 sessions_pa);
 int luo_session_serialize(void);
 int luo_session_deserialize(void);
 
-int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd);
+int luo_preserve_file(struct luo_file_set *file_set, u64 token, int fd,
+		      u64 arg);
 void luo_file_unpreserve_files(struct luo_file_set *file_set);
 int luo_file_freeze(struct luo_file_set *file_set,
 		    struct luo_file_set_ser *file_set_ser);
 void luo_file_unfreeze(struct luo_file_set *file_set,
 		       struct luo_file_set_ser *file_set_ser);
-int luo_retrieve_file(struct luo_file_set *file_set, u64 token,
+int luo_retrieve_file(struct luo_file_set *file_set, u64 token, u64 arg,
 		      struct file **filep);
 int luo_file_finish(struct luo_file_set *file_set);
 int luo_file_deserialize(struct luo_file_set *file_set,
diff --git a/kernel/liveupdate/luo_session.c b/kernel/liveupdate/luo_session.c
index f48e9a4185f9..ed9d53c7db77 100644
--- a/kernel/liveupdate/luo_session.c
+++ b/kernel/liveupdate/luo_session.c
@@ -267,7 +267,8 @@ static int luo_session_preserve_fd(struct luo_session *session,
 	int err;
 
 	guard(mutex)(&session->mutex);
-	err = luo_preserve_file(&session->file_set, argp->token, argp->fd);
+	err = luo_preserve_file(&session->file_set, argp->token, argp->fd,
+				argp->arg);
 	if (err)
 		return err;
 
@@ -290,7 +291,8 @@ static int luo_session_retrieve_fd(struct luo_session *session,
 		return argp->fd;
 
 	mutex_lock(&session->mutex);
-	err = luo_retrieve_file(&session->file_set, argp->token, &file);
+	err = luo_retrieve_file(&session->file_set, argp->token, argp->arg,
+				&file);
 	mutex_unlock(&session->mutex);
 	if (err < 0)
 		goto err_put_fd;
-- 
2.56.0.257.gf7497c7d27-goog

[PATCH v2 02/10] selftests: liveupdate: Add tests for preserve and retrieve user argument

[David Matlack]

From: Pasha Tatashin <pasha.tatashin@soleen.com>

Verify the user argument support in LIVEUPDATE_SESSION_PRESERVE_FD and
LIVEUPDATE_SESSION_RETRIEVE_FD. Add luo_session_preserve_fd_arg() and
luo_session_retrieve_fd_arg() helpers to libliveupdate so tests can pass
a handler-specific argument.

Add a preserve_memfd_with_arg test case to verify that memfd
preservation rejects a non-zero argument with -EOPNOTSUPP, accepts an
explicit zero argument, and remains compatible with callers passing the
legacy struct size up to the token field.

Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: David Matlack <dmatlack@google.com>
---
 .../liveupdate/lib/include/libliveupdate.h    |  3 ++
 .../selftests/liveupdate/lib/lu_utils.c       | 17 ++++++-
 .../testing/selftests/liveupdate/liveupdate.c | 44 +++++++++++++++++++
 3 files changed, 62 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/liveupdate/lib/include/libliveupdate.h b/tools/testing/selftests/liveupdate/lib/include/libliveupdate.h
index fa07fed08364..cd1d843a0d3d 100644
--- a/tools/testing/selftests/liveupdate/lib/include/libliveupdate.h
+++ b/tools/testing/selftests/liveupdate/lib/include/libliveupdate.h
@@ -29,7 +29,10 @@ int luo_get_session_name(int session_fd, char *name, size_t name_len);
 
 int luo_ensure_nofile_limit(long min_limit);
 int luo_session_preserve_fd(int session_fd, int fd, __u64 token);
+int luo_session_preserve_fd_arg(int session_fd, int fd, __u64 token,
+				__u64 user_arg);
 int luo_session_retrieve_fd(int session_fd, __u64 token);
+int luo_session_retrieve_fd_arg(int session_fd, __u64 token, __u64 user_arg);
 
 int create_and_preserve_memfd(int session_fd, int token, const char *data);
 int restore_and_verify_memfd(int session_fd, int token, const char *expected_data);
diff --git a/tools/testing/selftests/liveupdate/lib/lu_utils.c b/tools/testing/selftests/liveupdate/lib/lu_utils.c
index 74d41115c281..db7a90b002cb 100644
--- a/tools/testing/selftests/liveupdate/lib/lu_utils.c
+++ b/tools/testing/selftests/liveupdate/lib/lu_utils.c
@@ -79,12 +79,14 @@ int luo_retrieve_session(int luo_fd, const char *name)
 	return arg.fd;
 }
 
-int luo_session_preserve_fd(int session_fd, int fd, __u64 token)
+int luo_session_preserve_fd_arg(int session_fd, int fd, __u64 token,
+				__u64 user_arg)
 {
 	struct liveupdate_session_preserve_fd arg = {
 		.size = sizeof(arg),
 		.fd = fd,
 		.token = token,
+		.arg = user_arg,
 	};
 
 	if (ioctl(session_fd, LIVEUPDATE_SESSION_PRESERVE_FD, &arg))
@@ -93,11 +95,17 @@ int luo_session_preserve_fd(int session_fd, int fd, __u64 token)
 	return 0;
 }
 
-int luo_session_retrieve_fd(int session_fd, __u64 token)
+int luo_session_preserve_fd(int session_fd, int fd, __u64 token)
+{
+	return luo_session_preserve_fd_arg(session_fd, fd, token, 0);
+}
+
+int luo_session_retrieve_fd_arg(int session_fd, __u64 token, __u64 user_arg)
 {
 	struct liveupdate_session_retrieve_fd arg = {
 		.size = sizeof(arg),
 		.token = token,
+		.arg = user_arg,
 	};
 
 	if (ioctl(session_fd, LIVEUPDATE_SESSION_RETRIEVE_FD, &arg))
@@ -106,6 +114,11 @@ int luo_session_retrieve_fd(int session_fd, __u64 token)
 	return arg.fd;
 }
 
+int luo_session_retrieve_fd(int session_fd, __u64 token)
+{
+	return luo_session_retrieve_fd_arg(session_fd, token, 0);
+}
+
 /* Helper function to get a session name via ioctl. */
 int luo_get_session_name(int session_fd, char *name, size_t name_len)
 {
diff --git a/tools/testing/selftests/liveupdate/liveupdate.c b/tools/testing/selftests/liveupdate/liveupdate.c
index 2dedd5fc2534..4c4272167635 100644
--- a/tools/testing/selftests/liveupdate/liveupdate.c
+++ b/tools/testing/selftests/liveupdate/liveupdate.c
@@ -20,6 +20,7 @@
 
 #include <errno.h>
 #include <fcntl.h>
+#include <stddef.h>
 #include <string.h>
 #include <sys/ioctl.h>
 #include <unistd.h>
@@ -530,4 +531,47 @@ TEST_F(liveupdate_device, preserve_many_files)
 	ASSERT_EQ(close(session_fd), 0);
 }
 
+/*
+ * Test Case: Preserve MemFD with User Argument
+ *
+ * Verifies that passing a non-zero user argument to memfd preservation fails
+ * with -EOPNOTSUPP, while passing a zero argument or using the minimum struct
+ * size without the arg field succeeds.
+ */
+TEST_F(liveupdate_device, preserve_memfd_with_arg)
+{
+	struct liveupdate_session_preserve_fd min_arg = {};
+	int session_fd, mem_fd1, mem_fd2;
+
+	self->fd1 = open(LIVEUPDATE_DEV, O_RDWR);
+	if (self->fd1 < 0 && errno == ENOENT)
+		SKIP(return, "%s does not exist", LIVEUPDATE_DEV);
+	ASSERT_GE(self->fd1, 0);
+
+	session_fd = luo_create_session(self->fd1, "preserve-arg-test");
+	ASSERT_GE(session_fd, 0);
+
+	mem_fd1 = memfd_create("arg-memfd-1", 0);
+	ASSERT_GE(mem_fd1, 0);
+
+	/* Non-zero arg is not supported by memfd handler */
+	EXPECT_EQ(luo_session_preserve_fd_arg(session_fd, mem_fd1, 0x1111, 1),
+		  -EOPNOTSUPP);
+
+	/* Legacy struct size (up to token) should zero-fill arg and succeed */
+	min_arg.size = offsetof(struct liveupdate_session_preserve_fd, arg);
+	min_arg.fd = mem_fd1;
+	min_arg.token = 0x1111;
+	ASSERT_EQ(ioctl(session_fd, LIVEUPDATE_SESSION_PRESERVE_FD, &min_arg), 0);
+
+	/* Explicit zero arg with full struct size should also succeed */
+	mem_fd2 = memfd_create("arg-memfd-2", 0);
+	ASSERT_GE(mem_fd2, 0);
+	ASSERT_EQ(luo_session_preserve_fd_arg(session_fd, mem_fd2, 0x2222, 0), 0);
+
+	ASSERT_EQ(close(session_fd), 0);
+	ASSERT_EQ(close(mem_fd1), 0);
+	ASSERT_EQ(close(mem_fd2), 0);
+}
+
 TEST_HARNESS_MAIN
-- 
2.56.0.257.gf7497c7d27-goog

[PATCH v2 03/10] liveupdate: Allow file handlers to mark retrieve failures as retryable

[David Matlack]

From: Pasha Tatashin <pasha.tatashin@soleen.com>

When luo_retrieve_file() invokes a handler's .retrieve() callback and it
returns an error, LUO currently records the error in
luo_file->retrieve_status and blocks any subsequent retrieve attempts.
This is necessary when the handler has already partially consumed or
freed the preserved KHO state.

However, with user arguments passed to .retrieve(), a handler may fail
early while validating caller-supplied parameters (such as a missing
argument, an invalid or read-only target file descriptor, or a non-empty
target file) before touching any preserved KHO state. In such cases,
userspace should be able to fix the argument and retry
LIVEUPDATE_SESSION_RETRIEVE_FD, and if the file is never retrieved,
.finish() must still run to release the preserved KHO state.

Add a retryable output flag to struct liveupdate_file_op_args. When a
handler sets args->retryable = true on error, luo_retrieve_file() leaves
luo_file->retrieve_status at 0 so the retrieve operation can be retried
and .finish() will still clean up the unconsumed preserved state if the
session is finished without retrieving the file.

Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: David Matlack <dmatlack@google.com>
---
 include/linux/liveupdate.h      | 11 ++++++++---
 include/uapi/linux/liveupdate.h |  7 ++++---
 kernel/liveupdate/luo_file.c    | 20 ++++++++++++++------
 3 files changed, 26 insertions(+), 12 deletions(-)

diff --git a/include/linux/liveupdate.h b/include/linux/liveupdate.h
index 7543f5d648d3..e4ad0bf78a5c 100644
--- a/include/linux/liveupdate.h
+++ b/include/linux/liveupdate.h
@@ -58,9 +58,13 @@ struct liveupdate_arg_spec {
  * @session:          The session this file belongs to.
  * @retrieve_status:  The retrieve status for the 'can_finish / finish'
  *                    operation. A value of 0 means the retrieve has not been
- *                    attempted, a positive value means the retrieve was
- *                    successful, and a negative value means the retrieve failed,
- *                    and the value is the error code of the call.
+ *                    attempted (or only failed with a retryable error), a
+ *                    positive value means the retrieve was successful, and a
+ *                    negative value means the retrieve permanently failed, and
+ *                    the value is the error code of the call.
+ * @retryable:        For .retrieve(): [OUT] Set to true by the callback on
+ *                    error when the preserved state has not been consumed and
+ *                    retrieval may be retried.
  * @file:             The file object. For retrieve: [OUT] The callback sets
  *                    this to the new file. For other ops: [IN] The caller sets
  *                    this to the file being operated on.
@@ -83,6 +87,7 @@ struct liveupdate_file_op_args {
 	struct liveupdate_file_handler *handler;
 	struct liveupdate_session *session;
 	int retrieve_status;
+	bool retryable;
 	struct file *file;
 	u64 serialized_data;
 	void *private_data;
diff --git a/include/uapi/linux/liveupdate.h b/include/uapi/linux/liveupdate.h
index e806752c2fc6..953ffe0823be 100644
--- a/include/uapi/linux/liveupdate.h
+++ b/include/uapi/linux/liveupdate.h
@@ -174,9 +174,10 @@ struct liveupdate_session_preserve_fd {
  * associated with the token and populates the @fd field with a new file
  * descriptor referencing the restored resource in the current (new) kernel.
  * This operation must be performed *before* signaling completion via
- * %LIVEUPDATE_IOCTL_FINISH. If a retrieve of a token fails, subsequent
- * attempts to retrieve the token fail with the same error code. Failed
- * retrieves are not retried.
+ * %LIVEUPDATE_IOCTL_FINISH. If a retrieve of a token fails after consuming
+ * preserved state, subsequent attempts to retrieve the token fail with the
+ * same error code. Early argument or target validation errors before
+ * preserved state is consumed leave the token intact and may be retried.
  *
  * Retrieving a token that was already retrieved successfully returns a new file
  * descriptor for the same file. The @arg only applies to the retrieve that
diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index eeeb3b5ff2fa..908ae124ea5e 100644
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -152,9 +152,10 @@ static DEFINE_XARRAY(luo_preserved_files);
  * @retrieve_status: Status code indicating whether a user/kernel in the new kernel has
  *                 successfully called retrieve() on this file. This prevents
  *                 multiple retrieval attempts. A value of 0 means a retrieve()
- *                 has not been attempted, a positive value means the retrieve()
- *                 was successful, and a negative value means the retrieve()
- *                 failed, and the value is the error code of the call.
+ *                 has not been attempted (or only failed with a retryable
+ *                 error), a positive value means the retrieve() was successful,
+ *                 and a negative value means the retrieve() permanently failed,
+ *                 and the value is the error code of the call.
  * @mutex:         A mutex that protects the fields of this specific instance
  *                 (e.g., @retrieved, @file), ensuring that operations like
  *                 retrieving or finishing a file are atomic.
@@ -604,7 +605,9 @@ void luo_file_unfreeze(struct luo_file_set *file_set,
  * The operation is idempotent: if a file has already been successfully
  * retrieved, this function will simply return a pointer to the existing
  * 'struct file' and report success without re-executing the retrieve
- * operation. This is handled by checking the 'retrieved' flag under a lock.
+ * operation. If a previous retrieve failed permanently, it returns that
+ * saved error code; if a previous retrieve failed with a retryable error
+ * before consuming preserved state, the retrieve operation is re-attempted.
  *
  * File retrieval can happen in any order; it is not bound by the order of
  * preservation.
@@ -671,8 +674,13 @@ int luo_retrieve_file(struct luo_file_set *file_set, u64 token, u64 arg,
 	err = luo_file->fh->ops->retrieve(&args);
 	kfree(args.arg);
 	if (err) {
-		/* Keep the error code for later use. */
-		luo_file->retrieve_status = err;
+		/*
+		 * Keep the error code for later use unless the handler marked
+		 * the failure as retryable (e.g. invalid user argument before
+		 * preserved state was consumed).
+		 */
+		if (!args.retryable)
+			luo_file->retrieve_status = err;
 		return err;
 	}
 
-- 
2.56.0.257.gf7497c7d27-goog

[PATCH v2 04/10] mm: Rename memfd_luo to shmem_luo

[David Matlack]

Rename the memfd Live Update file handler from memfd_luo to shmem_luo,
including the source file, its KHO ABI header, its documentation and its
Kconfig option (CONFIG_LIVEUPDATE_MEMFD to CONFIG_LIVEUPDATE_SHMEM).

The handler preserves shmem files. Today those are memfds, but following
commits extend it to other files on tmpfs mounts, for which the memfd
name is confusing. Preserving memfds created with MFD_HUGETLB, which are
hugetlbfs files, will need a separate handler, so naming the handler
after the filesystem that backs the files also avoids having to rename
it again then.

Don't change the compatible string of the handler, "memfd-v2". It is
matched against the preserved state from the previous kernel, so
changing it would break live updates from kernels that use the old
name. The serialized format doesn't change either.

Also clarify in the documentation that memfd means a memfd created
without MFD_HUGETLB, and name the ABI documentation after the handler.

No functional change intended.

Assisted-by: LLM
Signed-off-by: David Matlack <dmatlack@google.com>
---
 Documentation/core-api/liveupdate.rst         |   2 +-
 Documentation/mm/index.rst                    |   2 +-
 ...reservation.rst => shmem_preservation.rst} |   8 +-
 MAINTAINERS                                   |   4 +-
 include/linux/kho/abi/{memfd.h => shmem.h}    |  41 ++++---
 kernel/liveupdate/Kconfig                     |   2 +-
 mm/Makefile                                   |   2 +-
 mm/{memfd_luo.c => shmem_luo.c}               | 115 +++++++++---------
 8 files changed, 89 insertions(+), 87 deletions(-)
 rename Documentation/mm/{memfd_preservation.rst => shmem_preservation.rst} (66%)
 rename include/linux/kho/abi/{memfd.h => shmem.h} (65%)
 rename mm/{memfd_luo.c => shmem_luo.c} (81%)

diff --git a/Documentation/core-api/liveupdate.rst b/Documentation/core-api/liveupdate.rst
index 2bce2644eba2..669722002440 100644
--- a/Documentation/core-api/liveupdate.rst
+++ b/Documentation/core-api/liveupdate.rst
@@ -37,7 +37,7 @@ The following types of file descriptors can be preserved
 .. toctree::
    :maxdepth: 1
 
-   ../mm/memfd_preservation
+   ../mm/shmem_preservation
 
 Public API
 ==========
diff --git a/Documentation/mm/index.rst b/Documentation/mm/index.rst
index 13a79f5d092c..b8ab2f89002d 100644
--- a/Documentation/mm/index.rst
+++ b/Documentation/mm/index.rst
@@ -61,7 +61,7 @@ documentation, or deleted if it has served its purpose.
    hugetlbfs_reserv
    ksm
    memory-model
-   memfd_preservation
+   shmem_preservation
    mmu_notifier
    multigen_lru
    numa
diff --git a/Documentation/mm/memfd_preservation.rst b/Documentation/mm/shmem_preservation.rst
similarity index 66%
rename from Documentation/mm/memfd_preservation.rst
rename to Documentation/mm/shmem_preservation.rst
index c908a12dffa7..e79bf8afaa9e 100644
--- a/Documentation/mm/memfd_preservation.rst
+++ b/Documentation/mm/shmem_preservation.rst
@@ -4,16 +4,16 @@
 Memfd Preservation via LUO
 ==========================
 
-.. kernel-doc:: mm/memfd_luo.c
+.. kernel-doc:: mm/shmem_luo.c
    :doc: Memfd Preservation via LUO
 
 Memfd Preservation ABI
 ======================
 
-.. kernel-doc:: include/linux/kho/abi/memfd.h
-   :doc: memfd Live Update ABI
+.. kernel-doc:: include/linux/kho/abi/shmem.h
+   :doc: shmem Live Update ABI
 
-.. kernel-doc:: include/linux/kho/abi/memfd.h
+.. kernel-doc:: include/linux/kho/abi/shmem.h
    :internal:
 
 See Also
diff --git a/MAINTAINERS b/MAINTAINERS
index 5d1b58271989..742cdce14cf9 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -15184,14 +15184,14 @@ L:	linux-kernel@vger.kernel.org
 S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/liveupdate/linux.git
 F:	Documentation/core-api/liveupdate.rst
-F:	Documentation/mm/memfd_preservation.rst
+F:	Documentation/mm/shmem_preservation.rst
 F:	Documentation/userspace-api/liveupdate.rst
 F:	include/linux/kho/abi/
 F:	include/linux/liveupdate.h
 F:	include/uapi/linux/liveupdate.h
 F:	kernel/liveupdate/
 F:	lib/tests/liveupdate.c
-F:	mm/memfd_luo.c
+F:	mm/shmem_luo.c
 F:	tools/testing/selftests/liveupdate/
 
 LLC (802.2)
diff --git a/include/linux/kho/abi/memfd.h b/include/linux/kho/abi/shmem.h
similarity index 65%
rename from include/linux/kho/abi/memfd.h
rename to include/linux/kho/abi/shmem.h
index 08b10fea2afc..b61687e358a2 100644
--- a/include/linux/kho/abi/memfd.h
+++ b/include/linux/kho/abi/shmem.h
@@ -8,49 +8,50 @@
  * Pratyush Yadav <ptyadav@amazon.de>
  */
 
-#ifndef _LINUX_KHO_ABI_MEMFD_H
-#define _LINUX_KHO_ABI_MEMFD_H
+#ifndef _LINUX_KHO_ABI_SHMEM_H
+#define _LINUX_KHO_ABI_SHMEM_H
 
 #include <linux/types.h>
 #include <linux/kho/abi/kexec_handover.h>
 
 /**
- * DOC: memfd Live Update ABI
+ * DOC: shmem Live Update ABI
  *
- * memfd uses the ABI defined below for preserving its state across a kexec
- * reboot using the LUO.
+ * The shmem file handler, which preserves memfds created without
+ * ``MFD_HUGETLB``, uses the ABI defined below for preserving their state across
+ * a kexec reboot using the LUO.
  *
- * The state is serialized into a packed structure `struct memfd_luo_ser`
+ * The state is serialized into a packed structure `struct shmem_luo_ser`
  * which is handed over to the next kernel via the KHO mechanism.
  *
  * This interface is a contract. Any modification to the structure layout
  * constitutes a breaking change. Such changes require incrementing the
- * version number in the MEMFD_LUO_FH_COMPATIBLE string.
+ * version number in the SHMEM_LUO_FH_COMPATIBLE string.
  */
 
 /**
- * MEMFD_LUO_FOLIO_DIRTY - The folio is dirty.
+ * SHMEM_LUO_FOLIO_DIRTY - The folio is dirty.
  *
  * This flag indicates the folio contains data from user. A non-dirty folio is
  * one that was allocated (say using fallocate(2)) but not written to.
  */
-#define MEMFD_LUO_FOLIO_DIRTY		BIT(0)
+#define SHMEM_LUO_FOLIO_DIRTY		BIT(0)
 
 /**
- * MEMFD_LUO_FOLIO_UPTODATE - The folio is up-to-date.
+ * SHMEM_LUO_FOLIO_UPTODATE - The folio is up-to-date.
  *
  * An up-to-date folio has been zeroed out. shmem zeroes out folios on first
  * use. This flag tracks which folios need zeroing.
  */
-#define MEMFD_LUO_FOLIO_UPTODATE	BIT(1)
+#define SHMEM_LUO_FOLIO_UPTODATE	BIT(1)
 
 /**
- * struct memfd_luo_folio_ser - Serialized state of a single folio.
+ * struct shmem_luo_folio_ser - Serialized state of a single folio.
  * @pfn:       The page frame number of the folio.
  * @flags:     Flags to describe the state of the folio.
  * @index:     The page offset (pgoff_t) of the folio within the original file.
  */
-struct memfd_luo_folio_ser {
+struct shmem_luo_folio_ser {
 	u64 pfn:52;
 	u64 flags:12;
 	u64 index;
@@ -60,7 +61,7 @@ struct memfd_luo_folio_ser {
  * The set of seals this version supports preserving. If support for any new
  * seals is needed, add it here and bump version.
  */
-#define MEMFD_LUO_ALL_SEALS (F_SEAL_SEAL | \
+#define SHMEM_LUO_ALL_SEALS (F_SEAL_SEAL | \
 			     F_SEAL_SHRINK | \
 			     F_SEAL_GROW | \
 			     F_SEAL_WRITE | \
@@ -68,7 +69,7 @@ struct memfd_luo_folio_ser {
 			     F_SEAL_EXEC)
 
 /**
- * struct memfd_luo_ser - Main serialization structure for a memfd.
+ * struct shmem_luo_ser - Main serialization structure for a memfd.
  * @pos:       The file's current position (f_pos).
  * @size:      The total size of the file in bytes (i_size).
  * @seals:     The seals present on the memfd. The seals are uABI so it is safe
@@ -76,9 +77,9 @@ struct memfd_luo_folio_ser {
  * @flags:     Flags for the file. Unused flag bits must be set to 0.
  * @nr_folios: Number of folios in the folios array.
  * @folios:    KHO vmalloc descriptor pointing to the array of
- *             struct memfd_luo_folio_ser.
+ *             struct shmem_luo_folio_ser.
  */
-struct memfd_luo_ser {
+struct shmem_luo_ser {
 	u64 pos;
 	u64 size;
 	u32 seals;
@@ -87,7 +88,7 @@ struct memfd_luo_ser {
 	struct kho_vmalloc folios;
 } __packed;
 
-/* The compatibility string for memfd file handler */
-#define MEMFD_LUO_FH_COMPATIBLE	"memfd-v2"
+/* The compatibility string for the shmem file handler */
+#define SHMEM_LUO_FH_COMPATIBLE	"memfd-v2"
 
-#endif /* _LINUX_KHO_ABI_MEMFD_H */
+#endif /* _LINUX_KHO_ABI_SHMEM_H */
diff --git a/kernel/liveupdate/Kconfig b/kernel/liveupdate/Kconfig
index f50daee8eff0..9a1c49e2e0c4 100644
--- a/kernel/liveupdate/Kconfig
+++ b/kernel/liveupdate/Kconfig
@@ -69,7 +69,7 @@ config LIVEUPDATE
 
 	  If unsure, say N.
 
-config LIVEUPDATE_MEMFD
+config LIVEUPDATE_SHMEM
 	bool "Live update support for memfd"
 	depends on LIVEUPDATE
 	depends on MEMFD_CREATE
diff --git a/mm/Makefile b/mm/Makefile
index e7245cb88c66..cbdcc2c6b296 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -100,7 +100,7 @@ obj-$(CONFIG_NUMA) += memory-tiers.o
 obj-$(CONFIG_DEVICE_MIGRATION) += migrate_device.o
 obj-$(CONFIG_TRANSPARENT_HUGEPAGE) += huge_memory.o khugepaged.o
 obj-$(CONFIG_PAGE_COUNTER) += page_counter.o
-obj-$(CONFIG_LIVEUPDATE_MEMFD) += memfd_luo.o
+obj-$(CONFIG_LIVEUPDATE_SHMEM) += shmem_luo.o
 obj-$(CONFIG_MEMCG_V1) += memcontrol-v1.o
 obj-$(CONFIG_MEMCG) += memcontrol.o vmpressure.o
 ifdef CONFIG_BPF_SYSCALL
diff --git a/mm/memfd_luo.c b/mm/shmem_luo.c
similarity index 81%
rename from mm/memfd_luo.c
rename to mm/shmem_luo.c
index 6b68220275eb..b8d86055912d 100644
--- a/mm/memfd_luo.c
+++ b/mm/shmem_luo.c
@@ -18,6 +18,11 @@
  * Update Orchestrator (LUO) file preservation. This allows userspace to
  * transfer its memory contents to the next kernel after a kexec.
  *
+ * Here, a memfd is a memfd created without ``MFD_HUGETLB``, which is a shmem
+ * file on the kernel's internal shmem mount. Memfds created with
+ * ``MFD_HUGETLB`` are hugetlbfs files, which this file handler doesn't
+ * preserve. Preserving them fails with ``-ENOENT``.
+ *
  * The preservation is not intended to be transparent. Only select properties of
  * the file are preserved. All others are reset to default. The preserved
  * properties are described below.
@@ -26,10 +31,6 @@
  *    The LUO API is not stabilized yet, so the preserved properties of a memfd
  *    are also not stable and are subject to backwards incompatible changes.
  *
- * .. note::
- *    Currently a memfd backed by Hugetlb is not supported. Memfds created
- *    with ``MFD_HUGETLB`` will be rejected.
- *
  * Preserved Properties
  * ====================
  *
@@ -52,7 +53,7 @@
  *
  * Seals
  *   File seals set on the memfd are preserved and re-applied on restore.
- *   Only seals known to this LUO version (see ``MEMFD_LUO_ALL_SEALS``) may
+ *   Only seals known to this LUO version (see ``SHMEM_LUO_ALL_SEALS``) may
  *   be present; preservation fails with ``-EOPNOTSUPP`` otherwise.
  *
  * Non-Preserved Properties
@@ -75,7 +76,7 @@
 #include <linux/file.h>
 #include <linux/io.h>
 #include <linux/kexec_handover.h>
-#include <linux/kho/abi/memfd.h>
+#include <linux/kho/abi/shmem.h>
 #include <linux/liveupdate.h>
 #include <linux/shmem_fs.h>
 #include <linux/vmalloc.h>
@@ -84,13 +85,13 @@
 
 #include "internal.h"
 
-static int memfd_luo_preserve_folios(struct file *file,
+static int shmem_luo_preserve_folios(struct file *file,
 				     struct kho_vmalloc *kho_vmalloc,
-				     struct memfd_luo_folio_ser **out_folios_ser,
+				     struct shmem_luo_folio_ser **out_folios_ser,
 				     u64 *nr_foliosp)
 {
 	struct inode *inode = file_inode(file);
-	struct memfd_luo_folio_ser *folios_ser;
+	struct shmem_luo_folio_ser *folios_ser;
 	unsigned int max_folios;
 	long i, size, nr_pinned;
 	struct folio **folios;
@@ -145,7 +146,7 @@ static int memfd_luo_preserve_folios(struct file *file,
 	}
 
 	for (i = 0; i < nr_folios; i++) {
-		struct memfd_luo_folio_ser *pfolio = &folios_ser[i];
+		struct shmem_luo_folio_ser *pfolio = &folios_ser[i];
 		struct folio *folio = folios[i];
 
 		err = kho_preserve_folio(folio);
@@ -196,7 +197,7 @@ static int memfd_luo_preserve_folios(struct file *file,
 		folio_unlock(folio);
 
 		pfolio->pfn = folio_pfn(folio);
-		pfolio->flags = MEMFD_LUO_FOLIO_DIRTY | MEMFD_LUO_FOLIO_UPTODATE;
+		pfolio->flags = SHMEM_LUO_FOLIO_DIRTY | SHMEM_LUO_FOLIO_UPTODATE;
 		pfolio->index = folio->index;
 	}
 
@@ -227,8 +228,8 @@ static int memfd_luo_preserve_folios(struct file *file,
 	return err;
 }
 
-static void memfd_luo_unpreserve_folios(struct kho_vmalloc *kho_vmalloc,
-					struct memfd_luo_folio_ser *folios_ser,
+static void shmem_luo_unpreserve_folios(struct kho_vmalloc *kho_vmalloc,
+					struct shmem_luo_folio_ser *folios_ser,
 					u64 nr_folios)
 {
 	long i;
@@ -239,7 +240,7 @@ static void memfd_luo_unpreserve_folios(struct kho_vmalloc *kho_vmalloc,
 	kho_unpreserve_vmalloc(kho_vmalloc);
 
 	for (i = 0; i < nr_folios; i++) {
-		const struct memfd_luo_folio_ser *pfolio = &folios_ser[i];
+		const struct shmem_luo_folio_ser *pfolio = &folios_ser[i];
 		struct folio *folio;
 
 		if (!pfolio->pfn)
@@ -254,11 +255,11 @@ static void memfd_luo_unpreserve_folios(struct kho_vmalloc *kho_vmalloc,
 	vfree(folios_ser);
 }
 
-static int memfd_luo_preserve(struct liveupdate_file_op_args *args)
+static int shmem_luo_preserve(struct liveupdate_file_op_args *args)
 {
 	struct inode *inode = file_inode(args->file);
-	struct memfd_luo_folio_ser *folios_ser;
-	struct memfd_luo_ser *ser;
+	struct shmem_luo_folio_ser *folios_ser;
+	struct shmem_luo_ser *ser;
 	u64 nr_folios, inode_size;
 	int err = 0, seals;
 
@@ -279,7 +280,7 @@ static int memfd_luo_preserve(struct liveupdate_file_op_args *args)
 	}
 
 	/* Make sure the file only has the seals supported by this version. */
-	if (seals & ~MEMFD_LUO_ALL_SEALS) {
+	if (seals & ~SHMEM_LUO_ALL_SEALS) {
 		err = -EOPNOTSUPP;
 		goto err_free_ser;
 	}
@@ -299,7 +300,7 @@ static int memfd_luo_preserve(struct liveupdate_file_op_args *args)
 	ser->size = inode_size;
 	ser->seals = seals;
 
-	err = memfd_luo_preserve_folios(args->file, &ser->folios,
+	err = shmem_luo_preserve_folios(args->file, &ser->folios,
 					&folios_ser, &nr_folios);
 	if (err)
 		goto err_free_ser;
@@ -320,9 +321,9 @@ static int memfd_luo_preserve(struct liveupdate_file_op_args *args)
 	return err;
 }
 
-static int memfd_luo_freeze(struct liveupdate_file_op_args *args)
+static int shmem_luo_freeze(struct liveupdate_file_op_args *args)
 {
-	struct memfd_luo_ser *ser;
+	struct shmem_luo_ser *ser;
 
 	if (WARN_ON_ONCE(!args->serialized_data))
 		return -EINVAL;
@@ -338,10 +339,10 @@ static int memfd_luo_freeze(struct liveupdate_file_op_args *args)
 	return 0;
 }
 
-static void memfd_luo_unpreserve(struct liveupdate_file_op_args *args)
+static void shmem_luo_unpreserve(struct liveupdate_file_op_args *args)
 {
 	struct inode *inode = file_inode(args->file);
-	struct memfd_luo_ser *ser;
+	struct shmem_luo_ser *ser;
 
 	if (WARN_ON_ONCE(!args->serialized_data))
 		return;
@@ -351,20 +352,20 @@ static void memfd_luo_unpreserve(struct liveupdate_file_op_args *args)
 
 	ser = phys_to_virt(args->serialized_data);
 
-	memfd_luo_unpreserve_folios(&ser->folios, args->private_data,
+	shmem_luo_unpreserve_folios(&ser->folios, args->private_data,
 				    ser->nr_folios);
 
 	kho_unpreserve_free(ser);
 	inode_unlock(inode);
 }
 
-static void memfd_luo_discard_folios(const struct memfd_luo_folio_ser *folios_ser,
+static void shmem_luo_discard_folios(const struct shmem_luo_folio_ser *folios_ser,
 				     u64 nr_folios)
 {
 	u64 i;
 
 	for (i = 0; i < nr_folios; i++) {
-		const struct memfd_luo_folio_ser *pfolio = &folios_ser[i];
+		const struct shmem_luo_folio_ser *pfolio = &folios_ser[i];
 		struct folio *folio;
 		phys_addr_t phys;
 
@@ -383,10 +384,10 @@ static void memfd_luo_discard_folios(const struct memfd_luo_folio_ser *folios_se
 	}
 }
 
-static void memfd_luo_finish(struct liveupdate_file_op_args *args)
+static void shmem_luo_finish(struct liveupdate_file_op_args *args)
 {
-	struct memfd_luo_folio_ser *folios_ser;
-	struct memfd_luo_ser *ser;
+	struct shmem_luo_folio_ser *folios_ser;
+	struct shmem_luo_ser *ser;
 
 	/*
 	 * If retrieve was successful, nothing to do. If it failed, retrieve()
@@ -405,7 +406,7 @@ static void memfd_luo_finish(struct liveupdate_file_op_args *args)
 		if (!folios_ser)
 			goto out;
 
-		memfd_luo_discard_folios(folios_ser, ser->nr_folios);
+		shmem_luo_discard_folios(folios_ser, ser->nr_folios);
 		vfree(folios_ser);
 	}
 
@@ -413,8 +414,8 @@ static void memfd_luo_finish(struct liveupdate_file_op_args *args)
 	kho_restore_free(ser);
 }
 
-static int memfd_luo_retrieve_folios(struct file *file,
-				     struct memfd_luo_folio_ser *folios_ser,
+static int shmem_luo_retrieve_folios(struct file *file,
+				     struct shmem_luo_folio_ser *folios_ser,
 				     u64 nr_folios)
 {
 	struct inode *inode = file_inode(file);
@@ -425,7 +426,7 @@ static int memfd_luo_retrieve_folios(struct file *file,
 	long i;
 
 	for (i = 0; i < nr_folios; i++) {
-		const struct memfd_luo_folio_ser *pfolio = &folios_ser[i];
+		const struct shmem_luo_folio_ser *pfolio = &folios_ser[i];
 		phys_addr_t phys;
 		u64 index;
 		int flags;
@@ -463,9 +464,9 @@ static int memfd_luo_retrieve_folios(struct file *file,
 			goto unlock_folio;
 		}
 
-		if (flags & MEMFD_LUO_FOLIO_UPTODATE)
+		if (flags & SHMEM_LUO_FOLIO_UPTODATE)
 			folio_mark_uptodate(folio);
-		if (flags & MEMFD_LUO_FOLIO_DIRTY)
+		if (flags & SHMEM_LUO_FOLIO_DIRTY)
 			folio_mark_dirty(folio);
 
 		npages = folio_nr_pages(folio);
@@ -497,7 +498,7 @@ static int memfd_luo_retrieve_folios(struct file *file,
 	 * freed when the file is freed. Free the ones not added yet here.
 	 */
 	for (long j = i + 1; j < nr_folios; j++) {
-		const struct memfd_luo_folio_ser *pfolio = &folios_ser[j];
+		const struct shmem_luo_folio_ser *pfolio = &folios_ser[j];
 		phys_addr_t phys;
 
 		if (!pfolio->pfn)
@@ -514,10 +515,10 @@ static int memfd_luo_retrieve_folios(struct file *file,
 	return err;
 }
 
-static int memfd_luo_retrieve(struct liveupdate_file_op_args *args)
+static int shmem_luo_retrieve(struct liveupdate_file_op_args *args)
 {
-	struct memfd_luo_folio_ser *folios_ser;
-	struct memfd_luo_ser *ser;
+	struct shmem_luo_folio_ser *folios_ser;
+	struct shmem_luo_ser *ser;
 	struct file *file;
 	int err;
 
@@ -526,7 +527,7 @@ static int memfd_luo_retrieve(struct liveupdate_file_op_args *args)
 		return -EINVAL;
 
 	/* Make sure the file only has seals supported by this version. */
-	if (ser->seals & ~MEMFD_LUO_ALL_SEALS) {
+	if (ser->seals & ~SHMEM_LUO_ALL_SEALS) {
 		err = -EOPNOTSUPP;
 		goto free_ser;
 	}
@@ -558,7 +559,7 @@ static int memfd_luo_retrieve(struct liveupdate_file_op_args *args)
 			goto put_file;
 		}
 
-		err = memfd_luo_retrieve_folios(file, folios_ser, ser->nr_folios);
+		err = shmem_luo_retrieve_folios(file, folios_ser, ser->nr_folios);
 		vfree(folios_ser);
 		if (err)
 			goto put_file;
@@ -576,7 +577,7 @@ static int memfd_luo_retrieve(struct liveupdate_file_op_args *args)
 	return err;
 }
 
-static bool memfd_luo_can_preserve(struct liveupdate_file_handler *handler,
+static bool shmem_luo_can_preserve(struct liveupdate_file_handler *handler,
 				   struct file *file)
 {
 	struct inode *inode = file_inode(file);
@@ -584,30 +585,30 @@ static bool memfd_luo_can_preserve(struct liveupdate_file_handler *handler,
 	return shmem_file(file) && !inode->i_nlink;
 }
 
-static unsigned long memfd_luo_get_id(struct file *file)
+static unsigned long shmem_luo_get_id(struct file *file)
 {
 	return (unsigned long)file_inode(file);
 }
 
-static const struct liveupdate_file_ops memfd_luo_file_ops = {
-	.freeze = memfd_luo_freeze,
-	.finish = memfd_luo_finish,
-	.retrieve = memfd_luo_retrieve,
-	.preserve = memfd_luo_preserve,
-	.unpreserve = memfd_luo_unpreserve,
-	.can_preserve = memfd_luo_can_preserve,
-	.get_id = memfd_luo_get_id,
+static const struct liveupdate_file_ops shmem_luo_file_ops = {
+	.freeze = shmem_luo_freeze,
+	.finish = shmem_luo_finish,
+	.retrieve = shmem_luo_retrieve,
+	.preserve = shmem_luo_preserve,
+	.unpreserve = shmem_luo_unpreserve,
+	.can_preserve = shmem_luo_can_preserve,
+	.get_id = shmem_luo_get_id,
 	.owner = THIS_MODULE,
 };
 
-static struct liveupdate_file_handler memfd_luo_handler = {
-	.ops = &memfd_luo_file_ops,
-	.compatible = MEMFD_LUO_FH_COMPATIBLE,
+static struct liveupdate_file_handler shmem_luo_handler = {
+	.ops = &shmem_luo_file_ops,
+	.compatible = SHMEM_LUO_FH_COMPATIBLE,
 };
 
-static int __init memfd_luo_init(void)
+static int __init shmem_luo_init(void)
 {
-	int err = liveupdate_register_file_handler(&memfd_luo_handler);
+	int err = liveupdate_register_file_handler(&shmem_luo_handler);
 
 	if (err && err != -EOPNOTSUPP) {
 		pr_err("Could not register luo filesystem handler: %pe\n",
@@ -618,4 +619,4 @@ static int __init memfd_luo_init(void)
 
 	return 0;
 }
-late_initcall(memfd_luo_init);
+late_initcall(shmem_luo_init);
-- 
2.56.0.257.gf7497c7d27-goog

[PATCH v2 05/10] liveupdate: Don't WARN if tracking a retrieved file fails

[David Matlack]

Handle a failure to add a retrieved file to luo_preserved_files instead
of triggering a WARN_ON(). xa_insert() can fail with -ENOMEM, and
userspace can trigger that with LIVEUPDATE_SESSION_RETRIEVE_FD, so
warning about it lets userspace crash systems with panic_on_warn.

The handler has already consumed the preserved state when this happens,
so make the failure permanent. Keep the file until the file set is
finished, like any other retrieved file, so that its resources are not
released before then. Finishing the file set then erases the file from
luo_preserved_files, which does nothing for a file that was never added.

Fixes: 00d0b372374f ("liveupdate: prevent double management of files")
Assisted-by: LLM
Signed-off-by: David Matlack <dmatlack@google.com>
---
 kernel/liveupdate/luo_file.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index 908ae124ea5e..5a82e45b9062 100644
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -684,14 +684,25 @@ int luo_retrieve_file(struct luo_file_set *file_set, u64 token, u64 arg,
 		return err;
 	}
 
+	err = xa_insert(&luo_preserved_files,
+			luo_get_id(luo_file->fh, args.file), args.file,
+			GFP_KERNEL);
+	if (err) {
+		/*
+		 * The handler has consumed the preserved state, so the retrieve
+		 * can't be retried. Keep the file until the file set is
+		 * finished, so that its resources are released at the same
+		 * time as those of other retrieved files.
+		 */
+		luo_file->file = args.file;
+		luo_file->retrieve_status = err;
+		return err;
+	}
+
 	luo_file->file = args.file;
 	/* Get reference so we can keep this file in LUO until finish */
 	get_file(luo_file->file);
 
-	WARN_ON(xa_insert(&luo_preserved_files,
-			  luo_get_id(luo_file->fh, luo_file->file),
-			  luo_file->file, GFP_KERNEL));
-
 	*filep = luo_file->file;
 	luo_file->retrieve_status = 1;
 
-- 
2.56.0.257.gf7497c7d27-goog

[PATCH v2 06/10] mm/shmem_luo: Don't make early retrieve failures permanent

[David Matlack]

If shmem_luo_retrieve() fails before it starts restoring the folios,
mark the failure as retryable and return the error without freeing the
serialized state. Nothing has consumed the preserved state at that
point, so the retrieve can be tried again. If no retrieve succeeds,
finish() frees the preserved folios, like it does for a file that was
never retrieved.

This fixes leaking the preserved folios when one of these early steps
fails, e.g. because the file has seals that this kernel doesn't support.
The retrieve freed the serialized state but not the folios, and finish()
then skipped the file because its retrieve had failed.

Assisted-by: LLM
Signed-off-by: David Matlack <dmatlack@google.com>
---
 mm/shmem_luo.c | 33 ++++++++++++++++++++-------------
 1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/mm/shmem_luo.c b/mm/shmem_luo.c
index b8d86055912d..bcac1bbb3db3 100644
--- a/mm/shmem_luo.c
+++ b/mm/shmem_luo.c
@@ -390,9 +390,9 @@ static void shmem_luo_finish(struct liveupdate_file_op_args *args)
 	struct shmem_luo_ser *ser;
 
 	/*
-	 * If retrieve was successful, nothing to do. If it failed, retrieve()
-	 * already cleaned up everything it could. So nothing to do there
-	 * either. Only need to clean up when retrieve was not called.
+	 * If retrieve was successful, nothing to do. If it failed permanently,
+	 * retrieve() already cleaned up everything it could. So nothing to do
+	 * there either. Only need to clean up when the file was not retrieved.
 	 */
 	if (args->retrieve_status)
 		return;
@@ -526,11 +526,16 @@ static int shmem_luo_retrieve(struct liveupdate_file_op_args *args)
 	if (!ser)
 		return -EINVAL;
 
+	/*
+	 * Nothing has consumed the preserved state until the folios are
+	 * restored below, so failures before that can be retried. If no
+	 * retrieve succeeds, finish() frees the preserved state.
+	 */
+	args->retryable = true;
+
 	/* Make sure the file only has seals supported by this version. */
-	if (ser->seals & ~SHMEM_LUO_ALL_SEALS) {
-		err = -EOPNOTSUPP;
-		goto free_ser;
-	}
+	if (ser->seals & ~SHMEM_LUO_ALL_SEALS)
+		return -EOPNOTSUPP;
 
 	/*
 	 * The seals are preserved. Allow sealing here so they can be added
@@ -539,8 +544,7 @@ static int shmem_luo_retrieve(struct liveupdate_file_op_args *args)
 	file = memfd_alloc_file("", MFD_ALLOW_SEALING);
 	if (IS_ERR(file)) {
 		pr_err("failed to setup file: %pe\n", file);
-		err = PTR_ERR(file);
-		goto free_ser;
+		return PTR_ERR(file);
 	}
 
 	err = memfd_add_seals(file, ser->seals);
@@ -552,17 +556,20 @@ static int shmem_luo_retrieve(struct liveupdate_file_op_args *args)
 	vfs_setpos(file, ser->pos, MAX_LFS_FILESIZE);
 	i_size_write(file_inode(file), ser->size);
 
+	/* The preserved state is consumed from here on. */
+	args->retryable = false;
+
 	if (ser->nr_folios) {
 		folios_ser = kho_restore_vmalloc(&ser->folios);
 		if (!folios_ser) {
 			err = -EINVAL;
-			goto put_file;
+			goto free_ser;
 		}
 
 		err = shmem_luo_retrieve_folios(file, folios_ser, ser->nr_folios);
 		vfree(folios_ser);
 		if (err)
-			goto put_file;
+			goto free_ser;
 	}
 
 	args->file = file;
@@ -570,10 +577,10 @@ static int shmem_luo_retrieve(struct liveupdate_file_op_args *args)
 
 	return 0;
 
-put_file:
-	fput(file);
 free_ser:
 	kho_restore_free(ser);
+put_file:
+	fput(file);
 	return err;
 }
 
-- 
2.56.0.257.gf7497c7d27-goog

[PATCH v2 07/10] mm/shmem_luo: Retrieve tmpfs files onto a tmpfs mount chosen by userspace

[David Matlack]

Retrieve files that were preserved from a tmpfs mount onto a tmpfs mount
chosen by userspace, instead of as memfds on the internal tmpfs mount.
Record which mount a file was on with a new SHMEM_LUO_FLAG_TMPFS flag in
struct shmem_luo_ser, based on the superblock of the file. shmem_luo
already accepts unlinked tmpfs files, such as files created with
O_TMPFILE, and a following commit also accepts linked ones.

The mount a tmpfs file was on doesn't exist in the new kernel, and
userspace may want to put the file elsewhere anyway. So add struct
liveupdate_shmem_retrieve_arg, which userspace passes as the retrieve
argument of LIVEUPDATE_SESSION_RETRIEVE_FD. It is modeled on open(): The
kernel creates a new file as if by openat(dirfd, ".", O_TMPFILE | flags,
mode), so the file gets the owner, permission checks and security labels
of any new file in that directory, and is charged to that mount. The
kernel then fills the file with the preserved contents, size, position
and seals before returning it, so nothing else can access the file
before it is complete. Userspace links the file at the path it wants
with linkat(), or passes O_EXCL to keep it unlinked. Neither the path
nor any other inode attribute of the file is part of the preserved
state, which keeps them out of the KHO ABI.

Pass the flags from userspace to file_open_root(), so that the VFS
checks them like for open(). file_open_root() silently ignores unknown
flags and mode bits, so reject those like openat2() does. Also reject
O_PATH, with which file_open_root() would ignore O_TMPFILE and open the
directory.

Keep the type of the file: memfds can only be retrieved as memfds, and
files on tmpfs mounts only onto tmpfs mounts, so that e.g. a file
can't be moved off the mount whose size limit and quotas it was subject
to. Passing the argument when retrieving a memfd, or not passing it when
retrieving a file from a tmpfs mount, fails with -EINVAL. Unlinked tmpfs
files were retrieved as memfds until now, but nothing relies on that, as
the LUO uAPI is not stable yet.

Like the other failures before the folios are restored, problems with
the argument and with creating the file can be retried.

Assisted-by: LLM
Signed-off-by: David Matlack <dmatlack@google.com>
---
 Documentation/mm/shmem_preservation.rst |   8 +-
 include/linux/kho/abi/shmem.h           |  21 ++-
 include/uapi/linux/liveupdate.h         |  35 +++++
 kernel/liveupdate/Kconfig               |   6 +-
 mm/internal.h                           |   1 +
 mm/shmem.c                              |   9 ++
 mm/shmem_luo.c                          | 180 ++++++++++++++++++++----
 7 files changed, 221 insertions(+), 39 deletions(-)

diff --git a/Documentation/mm/shmem_preservation.rst b/Documentation/mm/shmem_preservation.rst
index e79bf8afaa9e..030a8f18680c 100644
--- a/Documentation/mm/shmem_preservation.rst
+++ b/Documentation/mm/shmem_preservation.rst
@@ -1,11 +1,11 @@
 .. SPDX-License-Identifier: GPL-2.0-or-later
 
-==========================
-Memfd Preservation via LUO
-==========================
+====================================
+Memfd and Tmpfs Preservation via LUO
+====================================
 
 .. kernel-doc:: mm/shmem_luo.c
-   :doc: Memfd Preservation via LUO
+   :doc: Memfd and Tmpfs Preservation via LUO
 
 Memfd Preservation ABI
 ======================
diff --git a/include/linux/kho/abi/shmem.h b/include/linux/kho/abi/shmem.h
index b61687e358a2..88ef7d49b5f3 100644
--- a/include/linux/kho/abi/shmem.h
+++ b/include/linux/kho/abi/shmem.h
@@ -18,8 +18,8 @@
  * DOC: shmem Live Update ABI
  *
  * The shmem file handler, which preserves memfds created without
- * ``MFD_HUGETLB``, uses the ABI defined below for preserving their state across
- * a kexec reboot using the LUO.
+ * ``MFD_HUGETLB`` and tmpfs files, uses the ABI defined below for preserving
+ * their state across a kexec reboot using the LUO.
  *
  * The state is serialized into a packed structure `struct shmem_luo_ser`
  * which is handed over to the next kernel via the KHO mechanism.
@@ -69,12 +69,25 @@ struct shmem_luo_folio_ser {
 			     F_SEAL_EXEC)
 
 /**
- * struct shmem_luo_ser - Main serialization structure for a memfd.
+ * SHMEM_LUO_FLAG_TMPFS - The file was on a tmpfs mount.
+ *
+ * Set for files that were not on the internal shmem mount that memfds are
+ * created on. Such a file is retrieved onto a tmpfs mount chosen by userspace,
+ * instead of as a memfd.
+ */
+#define SHMEM_LUO_FLAG_TMPFS		BIT(0)
+
+/* The set of flags this version supports. */
+#define SHMEM_LUO_ALL_FLAGS		SHMEM_LUO_FLAG_TMPFS
+
+/**
+ * struct shmem_luo_ser - Main serialization structure for a memfd or tmpfs file.
  * @pos:       The file's current position (f_pos).
  * @size:      The total size of the file in bytes (i_size).
  * @seals:     The seals present on the memfd. The seals are uABI so it is safe
  *             to directly use them in the ABI.
- * @flags:     Flags for the file. Unused flag bits must be set to 0.
+ * @flags:     Flags for the file (SHMEM_LUO_FLAG_*). Unused flag bits must be
+ *             set to 0.
  * @nr_folios: Number of folios in the folios array.
  * @folios:    KHO vmalloc descriptor pointing to the array of
  *             struct shmem_luo_folio_ser.
diff --git a/include/uapi/linux/liveupdate.h b/include/uapi/linux/liveupdate.h
index 953ffe0823be..a9dcc4fcc87b 100644
--- a/include/uapi/linux/liveupdate.h
+++ b/include/uapi/linux/liveupdate.h
@@ -247,4 +247,39 @@ struct liveupdate_session_get_name {
 #define LIVEUPDATE_SESSION_GET_NAME					\
 	_IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_SESSION_GET_NAME)
 
+/**
+ * struct liveupdate_shmem_retrieve_arg - Argument to retrieve a tmpfs file
+ * @size:  Input; sizeof(struct liveupdate_shmem_retrieve_arg)
+ * @dirfd: Input; A file descriptor for a directory on the tmpfs mount to create
+ *         the file on.
+ * @flags: Input; The flags of the file, like the flags argument of open(),
+ *         except for O_TMPFILE, which is implied, and O_PATH, which is not
+ *         allowed.
+ * @mode:  Input; The mode of the file, like the mode argument of open().
+ *
+ * Passed via &struct liveupdate_session_retrieve_fd.arg to retrieve a file that
+ * was preserved from a tmpfs mount. Such files can only be retrieved with this
+ * argument, and memfds, i.e. files that were preserved from the kernel's
+ * internal shmem mount, can only be retrieved without it. Otherwise, the
+ * retrieve fails with -EINVAL.
+ *
+ * The kernel creates a new file as if by openat(@dirfd, ".", O_TMPFILE |
+ * @flags, @mode), fills it with the preserved contents, and returns it in
+ * &struct liveupdate_session_retrieve_fd.fd. Like any O_TMPFILE file, the file
+ * is not linked into the filesystem. Userspace can link it with linkat(),
+ * unless @flags contains O_EXCL.
+ *
+ * If @flags contains unknown flags or O_PATH, if @mode contains unknown mode
+ * bits, or if @dirfd is not on a tmpfs mount, the retrieve fails with -EINVAL.
+ * If the file can't be created, the retrieve fails with the same errors as
+ * open(). A retrieve that fails before the preserved contents are restored can
+ * be retried.
+ */
+struct liveupdate_shmem_retrieve_arg {
+	__u32		size;
+	__s32		dirfd;
+	__aligned_u64	flags;
+	__aligned_u64	mode;
+};
+
 #endif /* _UAPI_LIVEUPDATE_H */
diff --git a/kernel/liveupdate/Kconfig b/kernel/liveupdate/Kconfig
index 9a1c49e2e0c4..61d01f5a336e 100644
--- a/kernel/liveupdate/Kconfig
+++ b/kernel/liveupdate/Kconfig
@@ -70,14 +70,14 @@ config LIVEUPDATE
 	  If unsure, say N.
 
 config LIVEUPDATE_SHMEM
-	bool "Live update support for memfd"
+	bool "Live update support for memfd and tmpfs files"
 	depends on LIVEUPDATE
 	depends on MEMFD_CREATE
 	depends on SHMEM
 	default LIVEUPDATE
 	help
-	  Enable live update support for memfd regions. This allows preserving
-	  memfd-backed memory across kernel live updates.
+	  Enable live update support for memfds and tmpfs files. This allows
+	  preserving their contents across kernel live updates.
 
 	  This can be used to back VM memory with memfds, allowing the guest
 	  memory to persist, or for other user workloads needing to preserve
diff --git a/mm/internal.h b/mm/internal.h
index 38b1165212c9..630ae0297dd5 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1436,6 +1436,7 @@ int shmem_add_to_page_cache(struct folio *folio,
 			    pgoff_t index, void *expected, gfp_t gfp);
 int shmem_inode_acct_blocks(struct inode *inode, long pages);
 bool shmem_recalc_inode(struct inode *inode, long alloced, long swapped);
+bool shmem_inode_on_internal_mount(const struct inode *inode);
 
 #ifdef CONFIG_SHRINKER_DEBUG
 static inline __printf(2, 0) int shrinker_debugfs_name_alloc(
diff --git a/mm/shmem.c b/mm/shmem.c
index 897fa2b61346..fe2be9300ae7 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -5860,6 +5860,15 @@ struct file *shmem_kernel_file_setup(const char *name, loff_t size,
 }
 EXPORT_SYMBOL_GPL(shmem_kernel_file_setup);
 
+/*
+ * Whether @inode is on the internal shmem mount, which is used by
+ * shmem_file_setup() and thus by memfd_create().
+ */
+bool shmem_inode_on_internal_mount(const struct inode *inode)
+{
+	return inode->i_sb == shm_mnt->mnt_sb;
+}
+
 /**
  * shmem_file_setup - get an unlinked file living in tmpfs
  * @name: name for dentry (to be seen in /proc/<pid>/maps)
diff --git a/mm/shmem_luo.c b/mm/shmem_luo.c
index bcac1bbb3db3..ecbeb37d33a8 100644
--- a/mm/shmem_luo.c
+++ b/mm/shmem_luo.c
@@ -9,19 +9,20 @@
  */
 
 /**
- * DOC: Memfd Preservation via LUO
+ * DOC: Memfd and Tmpfs Preservation via LUO
  *
  * Overview
  * ========
  *
- * Memory file descriptors (memfd) can be preserved over a kexec using the Live
- * Update Orchestrator (LUO) file preservation. This allows userspace to
- * transfer its memory contents to the next kernel after a kexec.
+ * Memory file descriptors (memfd) and tmpfs files can be preserved over a kexec
+ * using the Live Update Orchestrator (LUO) file preservation. This allows
+ * userspace to transfer its memory contents to the next kernel after a kexec.
  *
  * Here, a memfd is a memfd created without ``MFD_HUGETLB``, which is a shmem
- * file on the kernel's internal shmem mount. Memfds created with
- * ``MFD_HUGETLB`` are hugetlbfs files, which this file handler doesn't
- * preserve. Preserving them fails with ``-ENOENT``.
+ * file on the kernel's internal shmem mount, and a tmpfs file is a file on any
+ * other tmpfs mount. Memfds created with ``MFD_HUGETLB`` and other files on
+ * hugetlbfs are not shmem files, and this file handler doesn't preserve them.
+ * Preserving them fails with ``-ENOENT``.
  *
  * The preservation is not intended to be transparent. Only select properties of
  * the file are preserved. All others are reset to default. The preserved
@@ -29,12 +30,13 @@
  *
  * .. note::
  *    The LUO API is not stabilized yet, so the preserved properties of a memfd
- *    are also not stable and are subject to backwards incompatible changes.
+ *    or tmpfs file are also not stable and are subject to backwards
+ *    incompatible changes.
  *
  * Preserved Properties
  * ====================
  *
- * The following properties of the memfd are preserved across kexec:
+ * The following properties of the file are preserved across kexec:
  *
  * File Contents
  *   All data stored in the file is preserved.
@@ -49,10 +51,12 @@
  *
  * File Status Flags
  *   memfds are always opened with ``O_RDWR`` and ``O_LARGEFILE``. This property
- *   is maintained.
+ *   is maintained. The file status flags of tmpfs files are not preserved.
+ *   Userspace chooses the flags when retrieving them, as described in
+ *   "Retrieving Tmpfs Files" below.
  *
  * Seals
- *   File seals set on the memfd are preserved and re-applied on restore.
+ *   The seals of the file are preserved and re-applied on restore.
  *   Only seals known to this LUO version (see ``SHMEM_LUO_ALL_SEALS``) may
  *   be present; preservation fails with ``-EOPNOTSUPP`` otherwise.
  *
@@ -67,12 +71,50 @@
  *   A memfd can be created with the ``MFD_CLOEXEC`` flag that sets the
  *   ``FD_CLOEXEC`` on the file. This flag is not preserved and must be set
  *   again after restore via ``fcntl()``.
+ *
+ * Inode Attributes
+ *   The name, path, owner, mode, timestamps and extended attributes of the
+ *   file are not preserved.
+ *
+ * Retrieving Tmpfs Files
+ * ======================
+ *
+ * A tmpfs file can be retrieved onto any tmpfs mount that userspace chooses.
+ * The mount that the file was on doesn't exist in the new kernel, and userspace
+ * may want to put the file elsewhere anyway.
+ *
+ * To retrieve a tmpfs file, userspace passes a
+ * ``struct liveupdate_shmem_retrieve_arg`` to
+ * ``LIVEUPDATE_SESSION_RETRIEVE_FD``. The argument specifies a directory on the
+ * target mount, and the flags and mode of the new file. The kernel creates the
+ * file as if by ``openat(dirfd, ".", O_TMPFILE | flags, mode)``, so the file
+ * gets the same flags, owner, permission checks and security labels as any
+ * other new file in that directory. The kernel then fills the file with the
+ * preserved contents, size, position and seals before it returns the file, so
+ * nothing else can access the file before it is complete.
+ *
+ * Like any ``O_TMPFILE`` file, the new file is not linked into the filesystem.
+ * Userspace can link it at the path it wants with ``linkat()``, unless it asked
+ * for ``O_EXCL``. Like with ``open()``, the file must be opened for writing.
+ * LUO keeps the file open until the session is finished, so a retrieved binary
+ * can't be executed until then.
+ *
+ * The blocks of the file are charged to the target mount, so the size limit
+ * and quotas of the mount apply. If the file doesn't fit, the retrieve fails
+ * permanently, since the preserved contents have already been restored at that
+ * point. If the argument is invalid or the file can't be created, the retrieve
+ * fails before the preserved contents are restored, so it can be retried.
+ *
+ * memfds can only be retrieved as memfds, and files on tmpfs mounts can only be
+ * retrieved onto tmpfs mounts. Retrieving a memfd with the argument, or a tmpfs
+ * file without it, fails with ``-EINVAL``.
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/bits.h>
 #include <linux/err.h>
+#include <linux/fcntl.h>
 #include <linux/file.h>
 #include <linux/io.h>
 #include <linux/kexec_handover.h>
@@ -81,6 +123,7 @@
 #include <linux/shmem_fs.h>
 #include <linux/vmalloc.h>
 #include <linux/memfd.h>
+#include <uapi/linux/magic.h>
 #include <uapi/linux/memfd.h>
 
 #include "internal.h"
@@ -299,6 +342,8 @@ static int shmem_luo_preserve(struct liveupdate_file_op_args *args)
 
 	ser->size = inode_size;
 	ser->seals = seals;
+	if (!shmem_inode_on_internal_mount(inode))
+		ser->flags |= SHMEM_LUO_FLAG_TMPFS;
 
 	err = shmem_luo_preserve_folios(args->file, &ser->folios,
 					&folios_ser, &nr_folios);
@@ -515,6 +560,92 @@ static int shmem_luo_retrieve_folios(struct file *file,
 	return err;
 }
 
+/* Create the memfd to retrieve a file from the internal shmem mount into. */
+static struct file *shmem_luo_create_memfd(const struct liveupdate_shmem_retrieve_arg *arg,
+					   unsigned int seals)
+{
+	struct file *file;
+	int err;
+
+	/* memfds are retrieved as memfds, so there is nothing to choose. */
+	if (arg)
+		return ERR_PTR(-EINVAL);
+
+	/*
+	 * The seals are preserved. Allow sealing here so they can be added
+	 * later.
+	 */
+	file = memfd_alloc_file("", MFD_ALLOW_SEALING);
+	if (IS_ERR(file)) {
+		pr_err("failed to setup file: %pe\n", file);
+		return file;
+	}
+
+	err = memfd_add_seals(file, seals);
+	if (err) {
+		pr_err("failed to add seals: %pe\n", ERR_PTR(err));
+		fput(file);
+		return ERR_PTR(err);
+	}
+
+	return file;
+}
+
+/*
+ * Create the file to retrieve a file from a tmpfs mount into, on the tmpfs
+ * mount chosen by userspace.
+ */
+static struct file *shmem_luo_create_tmpfs_file(const struct liveupdate_shmem_retrieve_arg *arg,
+						unsigned int seals)
+{
+	struct file *file;
+	int err;
+
+	if (!arg)
+		return ERR_PTR(-EINVAL);
+
+	/*
+	 * Like openat2(), reject unknown flags and mode bits instead of
+	 * ignoring them. Also reject O_PATH, which would make file_open_root()
+	 * ignore O_TMPFILE and open the directory instead of creating a file.
+	 */
+	if (arg->flags & ~(u64)VALID_OPEN_FLAGS || arg->flags & O_PATH ||
+	    arg->mode & ~(u64)S_IALLUGO)
+		return ERR_PTR(-EINVAL);
+
+	CLASS(fd_raw, dir)(arg->dirfd);
+	if (fd_empty(dir))
+		return ERR_PTR(-EBADF);
+
+	if (fd_file(dir)->f_path.dentry->d_sb->s_magic != TMPFS_MAGIC)
+		return ERR_PTR(-EINVAL);
+
+	/*
+	 * Create the file like open(O_TMPFILE) does, so that it gets the same
+	 * flag checks, permission checks, owner and security labels.
+	 */
+	file = file_open_root(&fd_file(dir)->f_path, ".",
+			      O_TMPFILE | O_LARGEFILE | arg->flags, arg->mode);
+	if (IS_ERR(file))
+		return file;
+
+	/*
+	 * Nothing else can access the new file yet, so set the preserved seals
+	 * directly. memfd_add_seals() refuses to, since files on tmpfs mounts
+	 * are created with F_SEAL_SEAL.
+	 */
+	if (seals & F_SEAL_WRITE) {
+		err = mapping_deny_writable(file->f_mapping);
+		if (err) {
+			fput(file);
+			return ERR_PTR(err);
+		}
+	}
+	SHMEM_I(file_inode(file))->seals = seals;
+
+	return file;
+}
+
 static int shmem_luo_retrieve(struct liveupdate_file_op_args *args)
 {
 	struct shmem_luo_folio_ser *folios_ser;
@@ -533,25 +664,18 @@ static int shmem_luo_retrieve(struct liveupdate_file_op_args *args)
 	 */
 	args->retryable = true;
 
-	/* Make sure the file only has seals supported by this version. */
-	if (ser->seals & ~SHMEM_LUO_ALL_SEALS)
+	/* Make sure the file only has seals and flags this version supports. */
+	if ((ser->seals & ~SHMEM_LUO_ALL_SEALS) ||
+	    (ser->flags & ~SHMEM_LUO_ALL_FLAGS))
 		return -EOPNOTSUPP;
 
-	/*
-	 * The seals are preserved. Allow sealing here so they can be added
-	 * later.
-	 */
-	file = memfd_alloc_file("", MFD_ALLOW_SEALING);
-	if (IS_ERR(file)) {
-		pr_err("failed to setup file: %pe\n", file);
+	/* Retrieve memfds as memfds, and other files onto a tmpfs mount. */
+	if (ser->flags & SHMEM_LUO_FLAG_TMPFS)
+		file = shmem_luo_create_tmpfs_file(args->arg, ser->seals);
+	else
+		file = shmem_luo_create_memfd(args->arg, ser->seals);
+	if (IS_ERR(file))
 		return PTR_ERR(file);
-	}
-
-	err = memfd_add_seals(file, ser->seals);
-	if (err) {
-		pr_err("failed to add seals: %pe\n", ERR_PTR(err));
-		goto put_file;
-	}
 
 	vfs_setpos(file, ser->pos, MAX_LFS_FILESIZE);
 	i_size_write(file_inode(file), ser->size);
@@ -579,7 +703,6 @@ static int shmem_luo_retrieve(struct liveupdate_file_op_args *args)
 
 free_ser:
 	kho_restore_free(ser);
-put_file:
 	fput(file);
 	return err;
 }
@@ -605,6 +728,7 @@ static const struct liveupdate_file_ops shmem_luo_file_ops = {
 	.unpreserve = shmem_luo_unpreserve,
 	.can_preserve = shmem_luo_can_preserve,
 	.get_id = shmem_luo_get_id,
+	.rarg = LIVEUPDATE_ARG(struct liveupdate_shmem_retrieve_arg, mode),
 	.owner = THIS_MODULE,
 };
 
-- 
2.56.0.257.gf7497c7d27-goog

[PATCH v2 08/10] mm/shmem_luo: Allow preserving tmpfs files that are still linked

[David Matlack]

shmem_luo already accepts any shmem file without links, which includes
unlinked tmpfs files and files created with O_TMPFILE. Also accept tmpfs
files that are still linked, so that userspace doesn't have to unlink
files to preserve them and can keep using them by path until the live
update.

The path of the file isn't preserved. Like other files from tmpfs
mounts, a linked file is retrieved onto a tmpfs mount chosen by
userspace, which can then link it at the path it wants.

While a file is preserved, its size is frozen, so truncating it,
fallocate() and writes past its end fail with -EPERM. For a linked file,
this affects everyone who opens the file by its path, so a caller that
can only read the file, e.g. a world-readable file in /dev/shm, could
use it to break the owner of the file. So require permission to write to
the file to preserve it, for all files. Like FS_IOC_ENABLE_VERITY, don't
require a file opened for writing, so that binaries that are being
executed can still be preserved through read-only fds, nor a writable
mount. If the size of the file can't change anyway, because it is
immutable or on a read-only superblock, also let its owner preserve it.
Don't let others do that, since the size could change again once the
file is made writable.

Preserving a file also fills its holes, but don't require any permission
for that. Anyone who can read a tmpfs file can already fill its holes by
faulting them in through a read-only mapping, also on read-only mounts
and for immutable files.

Document the frozen size and the permission requirement.

Assisted-by: LLM
Signed-off-by: David Matlack <dmatlack@google.com>
---
 mm/shmem_luo.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 52 insertions(+), 3 deletions(-)

diff --git a/mm/shmem_luo.c b/mm/shmem_luo.c
index ecbeb37d33a8..aba2bc1f18c5 100644
--- a/mm/shmem_luo.c
+++ b/mm/shmem_luo.c
@@ -28,6 +28,23 @@
  * the file are preserved. All others are reset to default. The preserved
  * properties are described below.
  *
+ * A tmpfs file can be preserved even if it is linked, but its path is not
+ * preserved. Userspace chooses where to put the file when retrieving it, as
+ * described in "Retrieving Tmpfs Files" below.
+ *
+ * Preserving a file requires permission to write to it, since preserving it
+ * affects all of its users, as described below. But the file doesn't need to
+ * be opened for writing. For example, a binary that is being executed can be
+ * preserved through a read-only file descriptor. The owner of a file whose
+ * size can't change anyway, because it is immutable or on a read-only
+ * superblock, may also preserve it. The file can be preserved through a
+ * read-only mount.
+ *
+ * While a file is preserved, its size can't change and no holes can be punched
+ * into it. Truncating the file, ``fallocate()`` and writes past the end of the
+ * file fail with ``-EPERM``. This applies to all users of the file, including
+ * users that open it by its path.
+ *
  * .. note::
  *    The LUO API is not stabilized yet, so the preserved properties of a memfd
  *    or tmpfs file are also not stable and are subject to backwards
@@ -298,6 +315,34 @@ static void shmem_luo_unpreserve_folios(struct kho_vmalloc *kho_vmalloc,
 	vfree(folios_ser);
 }
 
+/*
+ * Check whether the caller may preserve @file. Preserving the file freezes its
+ * size until it is unpreserved, for all users of the file, so require
+ * permission to write to the file. Like FS_IOC_ENABLE_VERITY, don't require a
+ * file opened for writing, so that e.g. a binary that is being executed can be
+ * preserved, nor a writable mount. If the size of the file can't change
+ * anyway, because it is on a read-only superblock or immutable, its owner may
+ * also preserve it. The size could only change again after the file is made
+ * writable, which is up to the owner or root.
+ *
+ * Preserving the file also fills its holes, but that doesn't need any
+ * permission: Anyone who can read the file can fill its holes by faulting
+ * them in through a read-only mapping.
+ */
+static int shmem_luo_may_preserve(struct file *file)
+{
+	struct mnt_idmap *idmap = file_mnt_idmap(file);
+	struct inode *inode = file_inode(file);
+	int err;
+
+	err = inode_permission(idmap, inode, MAY_WRITE);
+	if (err && (sb_rdonly(inode->i_sb) || IS_IMMUTABLE(inode)) &&
+	    inode_owner_or_capable(idmap, inode))
+		return 0;
+
+	return err;
+}
+
 static int shmem_luo_preserve(struct liveupdate_file_op_args *args)
 {
 	struct inode *inode = file_inode(args->file);
@@ -307,6 +352,11 @@ static int shmem_luo_preserve(struct liveupdate_file_op_args *args)
 	int err = 0, seals;
 
 	inode_lock(inode);
+
+	err = shmem_luo_may_preserve(args->file);
+	if (err)
+		goto err_unlock_inode;
+
 	shmem_freeze(inode, true);
 
 	/* Allocate the main serialization structure in preserved memory */
@@ -362,6 +412,7 @@ static int shmem_luo_preserve(struct liveupdate_file_op_args *args)
 	kho_unpreserve_free(ser);
 err_unlock:
 	shmem_freeze(inode, false);
+err_unlock_inode:
 	inode_unlock(inode);
 	return err;
 }
@@ -710,9 +761,7 @@ static int shmem_luo_retrieve(struct liveupdate_file_op_args *args)
 static bool shmem_luo_can_preserve(struct liveupdate_file_handler *handler,
 				   struct file *file)
 {
-	struct inode *inode = file_inode(file);
-
-	return shmem_file(file) && !inode->i_nlink;
+	return shmem_file(file);
 }
 
 static unsigned long shmem_luo_get_id(struct file *file)
-- 
2.56.0.257.gf7497c7d27-goog

[PATCH v2 09/10] mm/shmem_luo: Allow retrieving tmpfs files with O_RDONLY

[David Matlack]

Allow userspace to pass O_RDONLY in struct liveupdate_shmem_retrieve_arg
to retrieve a tmpfs file read-only.

open() requires write access for O_TMPFILE, so create the file writable
like before, then reopen it read-only with dentry_open() using the same
flags, and drop the writable file. Like open(), which grants the
requested access to a new file regardless of its mode, don't check
permission for the read-only open.

Retrieving a file read-only allows a restored binary to be executed
before the session is finished. LUO keeps the retrieved file open until
then, and executing a binary that is open for writing fails with
-ETXTBSY. Being able to execute restored binaries right away matters
when they are needed to finish restoring the system, e.g. to bring up
the services that retrieve and finish the remaining sessions.

Assisted-by: LLM
Signed-off-by: David Matlack <dmatlack@google.com>
---
 include/uapi/linux/liveupdate.h |  6 +++---
 mm/shmem_luo.c                  | 28 +++++++++++++++++++++-------
 2 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/include/uapi/linux/liveupdate.h b/include/uapi/linux/liveupdate.h
index a9dcc4fcc87b..790742a247e8 100644
--- a/include/uapi/linux/liveupdate.h
+++ b/include/uapi/linux/liveupdate.h
@@ -265,9 +265,9 @@ struct liveupdate_session_get_name {
  *
  * The kernel creates a new file as if by openat(@dirfd, ".", O_TMPFILE |
  * @flags, @mode), fills it with the preserved contents, and returns it in
- * &struct liveupdate_session_retrieve_fd.fd. Like any O_TMPFILE file, the file
- * is not linked into the filesystem. Userspace can link it with linkat(),
- * unless @flags contains O_EXCL.
+ * &struct liveupdate_session_retrieve_fd.fd. Unlike open(), O_RDONLY is
+ * allowed. Like any O_TMPFILE file, the file is not linked into the filesystem.
+ * Userspace can link it with linkat(), unless @flags contains O_EXCL.
  *
  * If @flags contains unknown flags or O_PATH, if @mode contains unknown mode
  * bits, or if @dirfd is not on a tmpfs mount, the retrieve fails with -EINVAL.
diff --git a/mm/shmem_luo.c b/mm/shmem_luo.c
index aba2bc1f18c5..0b4a9d6e2968 100644
--- a/mm/shmem_luo.c
+++ b/mm/shmem_luo.c
@@ -112,9 +112,10 @@
  *
  * Like any ``O_TMPFILE`` file, the new file is not linked into the filesystem.
  * Userspace can link it at the path it wants with ``linkat()``, unless it asked
- * for ``O_EXCL``. Like with ``open()``, the file must be opened for writing.
- * LUO keeps the file open until the session is finished, so a retrieved binary
- * can't be executed until then.
+ * for ``O_EXCL``. Unlike ``open()``, the file can be retrieved with
+ * ``O_RDONLY``. LUO keeps the file open until the session is finished, so a
+ * binary retrieved with ``O_RDWR`` or ``O_WRONLY`` can't be executed until
+ * then.
  *
  * The blocks of the file are charged to the target mount, so the size limit
  * and quotas of the mount apply. If the file doesn't fit, the retrieve fails
@@ -649,7 +650,9 @@ static struct file *shmem_luo_create_memfd(const struct liveupdate_shmem_retriev
 static struct file *shmem_luo_create_tmpfs_file(const struct liveupdate_shmem_retrieve_arg *arg,
 						unsigned int seals)
 {
-	struct file *file;
+	struct file *file, *ro_file;
+	bool rdonly;
+	int flags;
 	int err;
 
 	if (!arg)
@@ -673,10 +676,16 @@ static struct file *shmem_luo_create_tmpfs_file(const struct liveupdate_shmem_re
 
 	/*
 	 * Create the file like open(O_TMPFILE) does, so that it gets the same
-	 * flag checks, permission checks, owner and security labels.
+	 * flag checks, permission checks, owner and security labels. open()
+	 * requires write access for O_TMPFILE, so create the file writable and
+	 * reopen it read-only below if that is what userspace asked for. LUO
+	 * keeps the file until the session is finished, and a file opened for
+	 * writing couldn't be executed until then.
 	 */
+	flags = O_TMPFILE | O_LARGEFILE | arg->flags;
+	rdonly = (flags & O_ACCMODE) == O_RDONLY;
 	file = file_open_root(&fd_file(dir)->f_path, ".",
-			      O_TMPFILE | O_LARGEFILE | arg->flags, arg->mode);
+			      flags | (rdonly ? O_RDWR : 0), arg->mode);
 	if (IS_ERR(file))
 		return file;
 
@@ -694,7 +703,12 @@ static struct file *shmem_luo_create_tmpfs_file(const struct liveupdate_shmem_re
 	}
 	SHMEM_I(file_inode(file))->seals = seals;
 
-	return file;
+	if (!rdonly)
+		return file;
+
+	ro_file = dentry_open(&file->f_path, flags, current_cred());
+	fput(file);
+	return ro_file;
 }
 
 static int shmem_luo_retrieve(struct liveupdate_file_op_args *args)
-- 
2.56.0.257.gf7497c7d27-goog

[PATCH v2 10/10] selftests/liveupdate: Add a test for preserving tmpfs files

[David Matlack]

Add luo_tmpfs, a kexec test for preserving tmpfs files and memfds, and
for retrieving tmpfs files onto a tmpfs mount with struct
liveupdate_shmem_retrieve_arg.

Stage 1 preserves the source files of each test case. Stage 2 runs
each test case in its own directory, with its own tmpfs mounts, so that
block usage can be checked exactly with statfs() and st_blocks. The test
cases cover:

 - The restored file: contents, size, position, seals and holes, for
   linked and unlinked source files.

 - Creating the file: it is created like with open(O_TMPFILE), with the
   requested mode minus the umask, owned by the caller, and not linked
   until userspace links it, unless it asked for O_EXCL. Also O_RDONLY
   and O_WRONLY files, other open() flags such as O_APPEND and
   O_NONBLOCK, read-only mounts, and directories that the caller can't
   write to.

 - Preserving files that can't be written to: a binary while it is
   executed, through a read-only fd, files on read-only mounts and
   superblocks, and immutable files, including sparse ones, whose holes
   are filled. Preserving someone else's file that the caller can't
   write to fails.

 - Executing restored binaries: a restored binary can be executed
   before the session is finished if it was retrieved with O_RDONLY, but
   not if it was retrieved for writing, since LUO keeps the file open
   until then. These test cases execute copies of the test binary.

 - Block accounting: the file fits a mount of exactly its size, and a
   large folio that extends past the end of the file is charged in full.
   Running out of space, or hitting the memcg limit, fails permanently,
   and leaves nothing charged to the mount or the memcg. The session can
   still be finished.

 - memfds: they are only retrieved as memfds, with their seals, and
   files from tmpfs mounts only onto a tmpfs mount.

 - Interactions with LUO: invalid arguments, which can be retried,
   retrieving a token twice, and outgoing sessions.

Also check that the size of a preserved file is frozen, and that the
test doesn't trigger kernel warnings.

Enable CONFIG_TRANSPARENT_HUGEPAGE for the large folio test cases,
CONFIG_MEMCG for the memcg test case and CONFIG_TMPFS_XATTR for
FS_IOC_SETFLAGS. Those test cases are skipped without them.

tmpfs quotas are not tested, since the test runs as root, which is not
subject to quota limits.

Assisted-by: LLM
Signed-off-by: David Matlack <dmatlack@google.com>
---
 tools/testing/selftests/liveupdate/Makefile   |    1 +
 tools/testing/selftests/liveupdate/config     |    4 +
 .../testing/selftests/liveupdate/luo_tmpfs.c  | 2000 +++++++++++++++++
 .../selftests/liveupdate/run-vmtests.sh       |    1 +
 4 files changed, 2006 insertions(+)
 create mode 100644 tools/testing/selftests/liveupdate/luo_tmpfs.c

diff --git a/tools/testing/selftests/liveupdate/Makefile b/tools/testing/selftests/liveupdate/Makefile
index 634211c66652..e217008db3a7 100644
--- a/tools/testing/selftests/liveupdate/Makefile
+++ b/tools/testing/selftests/liveupdate/Makefile
@@ -6,6 +6,7 @@ TEST_GEN_PROGS_EXTENDED += luo_kexec_simple
 TEST_GEN_PROGS_EXTENDED += luo_multi_session
 TEST_GEN_PROGS_EXTENDED += luo_stress_sessions
 TEST_GEN_PROGS_EXTENDED += luo_stress_files
+TEST_GEN_PROGS_EXTENDED += luo_tmpfs
 
 TEST_FILES += do_kexec.sh
 
diff --git a/tools/testing/selftests/liveupdate/config b/tools/testing/selftests/liveupdate/config
index 016d009dba13..7f38291c979d 100644
--- a/tools/testing/selftests/liveupdate/config
+++ b/tools/testing/selftests/liveupdate/config
@@ -1,4 +1,5 @@
 CONFIG_BLK_DEV_INITRD=y
+CONFIG_CGROUPS=y
 CONFIG_DEVTMPFS=y
 CONFIG_KEXEC_FILE=y
 CONFIG_KEXEC_HANDOVER=y
@@ -7,6 +8,9 @@ CONFIG_KEXEC_HANDOVER_DEBUGFS=y
 CONFIG_KEXEC_HANDOVER_DEBUG=y
 CONFIG_LIVEUPDATE=y
 CONFIG_LIVEUPDATE_TEST=y
+CONFIG_MEMCG=y
 CONFIG_MEMFD_CREATE=y
 CONFIG_TMPFS=y
+CONFIG_TMPFS_XATTR=y
 CONFIG_SHMEM=y
+CONFIG_TRANSPARENT_HUGEPAGE=y
diff --git a/tools/testing/selftests/liveupdate/luo_tmpfs.c b/tools/testing/selftests/liveupdate/luo_tmpfs.c
new file mode 100644
index 000000000000..89639e74a6b2
--- /dev/null
+++ b/tools/testing/selftests/liveupdate/luo_tmpfs.c
@@ -0,0 +1,2000 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ * Copyright (c) 2026, Google LLC.
+ * David Matlack <dmatlack@google.com>
+ *
+ * Test the preservation of tmpfs files across a kexec, and retrieving them onto
+ * a tmpfs mount with struct liveupdate_shmem_retrieve_arg.
+ *
+ * Each test case preserves its source files in stage 1 and checks how they can
+ * be retrieved in stage 2. The cases use separate tokens, so that a failed case
+ * doesn't affect the others. In stage 2, each case mounts the tmpfs instances
+ * it needs, so that their block usage can be checked exactly.
+ */
+
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+
+/* sys/mman.h only defines the MFD_* flags that are not defined yet. */
+#include <linux/memfd.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/syscall.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include <linux/falloc.h>
+#include <linux/fs.h>
+
+#ifdef NOLIBC
+#include <asm/statfs.h>
+#else
+#include <sys/statfs.h>
+#endif
+
+#include <libliveupdate.h>
+
+#ifndef F_SEAL_FUTURE_WRITE
+#define F_SEAL_FUTURE_WRITE	0x0010
+#endif
+#ifndef F_SEAL_EXEC
+#define F_SEAL_EXEC		0x0020
+#endif
+#ifndef MNT_DETACH
+#define MNT_DETACH		2
+#endif
+#ifndef O_TMPFILE
+#define O_TMPFILE		(020000000 | O_DIRECTORY)
+#endif
+
+#define STATE_SESSION_NAME	"tmpfs_state"
+#define STATE_TOKEN		999
+#define SESSION_NAME		"tmpfs"
+
+/*
+ * Everything happens on a tmpfs mounted at TEST_DIR. In stage 1, the source
+ * files are created on the tmpfs mounted at TEST_DIR/src, or at
+ * TEST_DIR/src_huge for files that need large folios. In stage 2, each case
+ * runs in the directory TEST_DIR/<name of the case>.
+ */
+#define TEST_DIR		"/luo_tmpfs"
+
+#define SMALL_SIZE		8192
+#define SPARSE_PAGES		8
+#define NOBODY			65534
+#define TEST_UMASK		022
+
+/* The exec cases run copies of this test with EXEC_ARG, see exec_main(). */
+#define EXEC_ARG		"--exec"
+#define EXEC_STATUS		200
+
+/* TAINT_BAD_PAGE, TAINT_DIE and TAINT_WARN. */
+#define BAD_TAINT		((1L << 5) | (1L << 7) | (1L << 9))
+
+/*
+ * Checks for the test cases. On failure, they print the failed check and
+ * return KSFT_FAIL from the calling function.
+ */
+#define CHECK(cond) do {						\
+	if (!(cond)) {							\
+		ksft_print_msg("%s:%d: Check failed: %s (errno %d)\n",	\
+			       __func__, __LINE__, #cond, errno);	\
+		return KSFT_FAIL;					\
+	}								\
+} while (0)
+
+#define CHECK_EQ(expr, expected) do {					\
+	long long __val = (expr), __exp = (expected);			\
+									\
+	if (__val != __exp) {						\
+		ksft_print_msg("%s:%d: %s is %lld, expected %lld\n",	\
+			       __func__, __LINE__, #expr, __val, __exp); \
+		return KSFT_FAIL;					\
+	}								\
+} while (0)
+
+/* Check that a system call fails with @err. */
+#define CHECK_ERRNO(expr, err) do {					\
+	long __ret = (expr);						\
+	int __err = errno, __exp = (err);				\
+									\
+	if (__ret != -1 || __err != __exp) {				\
+		ksft_print_msg("%s:%d: %s: %ld, errno %d, expected %d\n", \
+			       __func__, __LINE__, #expr,		\
+			       __ret, __err, __exp);			\
+		return KSFT_FAIL;					\
+	}								\
+} while (0)
+
+/* Call a function that returns a KSFT_* code, and return if it fails. */
+#define TRY(expr) do {							\
+	int __ret = (expr);						\
+									\
+	if (__ret != KSFT_PASS) {					\
+		ksft_print_msg("%s:%d: %s failed\n",			\
+			       __func__, __LINE__, #expr);		\
+		return __ret;						\
+	}								\
+} while (0)
+
+struct test_case {
+	const char *name;
+	/* Size and file position of the source file. */
+	size_t size;
+	off_t pos;
+	/* Stage 1: Preserve the source files. Defaults to preserve_file(). */
+	int (*preserve)(struct test_case *tc);
+	/* Stage 2: Retrieve the files and check them. */
+	int (*verify)(struct test_case *tc);
+	/* Stage 2: Optional checks after the session is finished. */
+	int (*after_finish)(struct test_case *tc);
+	/* The tokens of the case are token to token + 0xff. */
+	__u64 token;
+	/* State kept from verify() for after_finish(). */
+	int result;
+};
+
+static unsigned long page_size;
+static int dev_fd;
+static int session_fd;
+static bool have_huge_src;
+
+/* nolibc doesn't have these, so use syscall() with both libcs. */
+static int do_fcntl(int fd, int cmd, long arg)
+{
+	return syscall(__NR_fcntl, fd, cmd, arg);
+}
+
+static int do_fallocate(int fd, int mode, off_t offset, off_t len)
+{
+	return syscall(__NR_fallocate, fd, mode, offset, len);
+}
+
+static int do_fchmod(int fd, mode_t mode)
+{
+	return syscall(__NR_fchmod, fd, mode);
+}
+
+static int do_mount(const char *source, const char *target, const char *type,
+		    unsigned long flags, const char *data)
+{
+	return syscall(__NR_mount, source, target, type, flags, data);
+}
+
+static int do_statfs(const char *path, struct statfs *buf)
+{
+#ifdef NOLIBC
+	return syscall(__NR_statfs, path, buf);
+#else
+	return statfs(path, buf);
+#endif
+}
+
+static unsigned long nr_pages(size_t size)
+{
+	return (size + page_size - 1) / page_size;
+}
+
+static long long file_size(int fd)
+{
+	struct stat st;
+
+	if (fstat(fd, &st))
+		return -1;
+
+	return st.st_size;
+}
+
+/* Return the number of pages charged to the file. */
+static long file_pages(int fd)
+{
+	struct stat st;
+
+	if (fstat(fd, &st))
+		return -1;
+
+	return st.st_blocks * 512 / page_size;
+}
+
+/* Return the number of pages used on the tmpfs mounted at @path. */
+static long mnt_used(const char *path)
+{
+	struct statfs buf;
+
+	if (do_statfs(path, &buf))
+		return -1;
+
+	return buf.f_blocks - buf.f_bfree;
+}
+
+static long mnt_free(const char *path)
+{
+	struct statfs buf;
+
+	if (do_statfs(path, &buf))
+		return -1;
+
+	return buf.f_bfree;
+}
+
+/* Mount a tmpfs with room for @pages pages at @dir. */
+static int mount_tmpfs(const char *dir, unsigned long pages, const char *opts)
+{
+	char data[64];
+
+	if (mkdir(dir, 0755) && errno != EEXIST)
+		return -errno;
+
+	snprintf(data, sizeof(data), "size=%lu%s%s", pages * page_size,
+		 opts ? "," : "", opts ? opts : "");
+	if (do_mount("tmpfs", dir, "tmpfs", 0, data))
+		return -errno;
+
+	return 0;
+}
+
+/* Read a number from the file at @path. Return -1 on failure. */
+static long read_long(const char *path)
+{
+	char buf[32] = {};
+	ssize_t len;
+	int fd;
+
+	fd = open(path, O_RDONLY);
+	if (fd < 0)
+		return -1;
+
+	len = read(fd, buf, sizeof(buf) - 1);
+	close(fd);
+	if (len <= 0)
+		return -1;
+
+	return strtol(buf, NULL, 10);
+}
+
+/* Write @str to the file at @path. Return 0 or -errno. */
+static int write_file(const char *path, const char *str)
+{
+	ssize_t len = strlen(str), ret;
+	int fd;
+
+	fd = open(path, O_WRONLY);
+	if (fd < 0)
+		return -errno;
+
+	ret = write(fd, str, len);
+	if (ret != len)
+		ret = ret < 0 ? -errno : -EIO;
+	else
+		ret = 0;
+
+	close(fd);
+	return ret;
+}
+
+/* Retrieve with the argument @arg. Return the new fd or -errno. */
+static int retrieve_arg(__u64 token, struct liveupdate_shmem_retrieve_arg *arg)
+{
+	return luo_session_retrieve_fd_arg(session_fd, token,
+					   (__u64)(uintptr_t)arg);
+}
+
+/*
+ * Retrieve the file preserved with @token onto the tmpfs mount of the
+ * directory @dir, with the access mode and flags @flags and the mode @mode.
+ * Return the new fd or -errno.
+ */
+static int retrieve_at(__u64 token, const char *dir, int flags, mode_t mode)
+{
+	struct liveupdate_shmem_retrieve_arg arg = {
+		.size = sizeof(arg),
+		.flags = flags,
+		.mode = mode,
+	};
+	int ret;
+
+	arg.dirfd = open(dir, O_PATH | O_DIRECTORY);
+	if (arg.dirfd < 0)
+		return -errno;
+
+	ret = retrieve_arg(token, &arg);
+	close(arg.dirfd);
+	return ret;
+}
+
+/* Link the unlinked file @fd at @path. */
+static int link_fd(int fd, const char *path)
+{
+	char fd_path[64];
+
+	snprintf(fd_path, sizeof(fd_path), "/proc/self/fd/%d", fd);
+	return syscall(__NR_linkat, AT_FDCWD, fd_path, AT_FDCWD, path,
+		       AT_SYMLINK_FOLLOW);
+}
+
+/* Open the file @fd again with @flags. */
+static int reopen_fd(int fd, int flags)
+{
+	char fd_path[64];
+
+	snprintf(fd_path, sizeof(fd_path), "/proc/self/fd/%d", fd);
+	return open(fd_path, flags);
+}
+
+/* The contents of the files depend on their token. */
+static unsigned char pattern(__u64 token, size_t offset)
+{
+	unsigned int word;
+
+	word = (offset / 4 + 1) * 2654435761u ^ token * 2246822519u;
+	return word >> (offset % 4 * 8);
+}
+
+static int write_pattern(int fd, size_t offset, size_t len, __u64 token)
+{
+	static unsigned char buf[65536];
+	size_t i, n;
+
+	if (lseek(fd, offset, SEEK_SET) != (off_t)offset)
+		return -1;
+
+	for (; len; offset += n, len -= n) {
+		n = len < sizeof(buf) ? len : sizeof(buf);
+		for (i = 0; i < n; i++)
+			buf[i] = pattern(token, offset + i);
+		if (write(fd, buf, n) != (ssize_t)n)
+			return -1;
+	}
+
+	return 0;
+}
+
+/*
+ * Check that [start, end) of @p has the contents of the file preserved with
+ * @token, or zeroes if @token is 0.
+ */
+static int check_range(const unsigned char *p, size_t start, size_t end,
+		       __u64 token)
+{
+	unsigned char expected;
+	size_t i;
+
+	for (i = start; i < end; i++) {
+		expected = token ? pattern(token, i) : 0;
+		if (p[i] != expected) {
+			ksft_print_msg("Byte %zu is %#x, expected %#x\n",
+				       i, p[i], expected);
+			return KSFT_FAIL;
+		}
+	}
+
+	return KSFT_PASS;
+}
+
+/* Check that the file has the first @size bytes of the pattern for @token. */
+static int check_contents(int fd, size_t size, __u64 token)
+{
+	size_t len = nr_pages(size) * page_size;
+	unsigned char *p;
+	int ret;
+
+	if (!size)
+		return KSFT_PASS;
+
+	p = mmap(NULL, len, PROT_READ, MAP_SHARED, fd, 0);
+	CHECK(p != MAP_FAILED);
+
+	ret = check_range(p, 0, size, token);
+	/* The rest of the last page must be zero. */
+	if (ret == KSFT_PASS)
+		ret = check_range(p, size, len, 0);
+
+	munmap(p, len);
+	return ret;
+}
+
+/* Check that @fd has the size, position and contents of the source of @tc. */
+static int check_restored(struct test_case *tc, int fd)
+{
+	CHECK_EQ(file_size(fd), tc->size);
+	CHECK_EQ(file_pages(fd), nr_pages(tc->size));
+	CHECK_EQ(lseek(fd, 0, SEEK_CUR), tc->pos);
+	return check_contents(fd, tc->size, tc->token);
+}
+
+/* Create a file with the first @size bytes of the pattern for @token. */
+static int create_source(const char *path, size_t size, __u64 token)
+{
+	int fd;
+
+	fd = open(path, O_CREAT | O_EXCL | O_RDWR, 0644);
+	if (fd < 0)
+		return -1;
+
+	if (write_pattern(fd, 0, size, token)) {
+		close(fd);
+		return -1;
+	}
+
+	return fd;
+}
+
+static int preserve_fd(int fd, off_t pos, __u64 token)
+{
+	CHECK_EQ(lseek(fd, pos, SEEK_SET), pos);
+	CHECK_EQ(luo_session_preserve_fd(session_fd, fd, token), 0);
+	return KSFT_PASS;
+}
+
+static int preserve_source(const char *path, size_t size, off_t pos,
+			   __u64 token)
+{
+	int fd, ret;
+
+	fd = create_source(path, size, token);
+	CHECK(fd >= 0);
+	ret = preserve_fd(fd, pos, token);
+	close(fd);
+
+	return ret;
+}
+
+/* The default for test_case.preserve(). */
+static int preserve_file(struct test_case *tc)
+{
+	char path[128];
+
+	snprintf(path, sizeof(path), "src/%s", tc->name);
+	return preserve_source(path, tc->size, tc->pos, tc->token);
+}
+
+/* Preserve a memfd with the contents of the source of @tc. */
+static int preserve_memfd(struct test_case *tc, unsigned int flags,
+			  unsigned int seals)
+{
+	int fd, ret;
+
+	fd = memfd_create(tc->name, flags);
+	CHECK(fd >= 0);
+	CHECK_EQ(write_pattern(fd, 0, tc->size, tc->token), 0);
+	if (seals)
+		CHECK_EQ(do_fcntl(fd, F_ADD_SEALS, seals), 0);
+	ret = preserve_fd(fd, tc->pos, tc->token);
+	close(fd);
+
+	return ret;
+}
+
+/* Preserve a file from the tmpfs mounted with huge=always. */
+static int preserve_huge_file(struct test_case *tc)
+{
+	char path[128];
+	int fd, ret;
+
+	if (!have_huge_src)
+		return KSFT_SKIP;
+
+	snprintf(path, sizeof(path), "src_huge/%s", tc->name);
+	fd = create_source(path, tc->size, tc->token);
+	CHECK(fd >= 0);
+
+	/* A file that ends within a page must end in a large folio. */
+	if (tc->size % page_size && file_pages(fd) <= nr_pages(tc->size)) {
+		ksft_print_msg("%s: No large folio for the source file\n",
+			       tc->name);
+		close(fd);
+		return KSFT_SKIP;
+	}
+
+	ret = preserve_fd(fd, tc->pos, tc->token);
+	close(fd);
+
+	return ret;
+}
+
+/* The large folio cases are only preserved if huge=always works. */
+static int skip_not_preserved(struct test_case *tc)
+{
+	ksft_print_msg("%s: The source file was not preserved\n", tc->name);
+	return KSFT_SKIP;
+}
+
+static int drop_privileges(void)
+{
+	CHECK_EQ(syscall(__NR_setgroups, 0, NULL), 0);
+	CHECK_EQ(syscall(__NR_setresgid, NOBODY, NOBODY, NOBODY), 0);
+	CHECK_EQ(syscall(__NR_setresuid, NOBODY, NOBODY, NOBODY), 0);
+	return KSFT_PASS;
+}
+
+/* Run @fn(@tc) in a child process, and return its result. */
+static int run_child(int (*fn)(struct test_case *tc), struct test_case *tc)
+{
+	int status, ret;
+	pid_t pid;
+
+	fflush(stdout);
+	pid = fork();
+	CHECK(pid >= 0);
+	if (!pid) {
+		ret = fn(tc);
+		fflush(stdout);
+		_exit(ret);
+	}
+
+	CHECK_EQ(waitpid(pid, &status, 0), pid);
+	CHECK(WIFEXITED(status));
+	return WEXITSTATUS(status);
+}
+
+/*
+ * A copy of this test that is executed with EXEC_ARG writes a 0 byte to stdout
+ * once it runs, and exits with EXEC_STATUS once stdin is closed.
+ */
+static int exec_main(void)
+{
+	char c;
+
+	if (write(STDOUT_FILENO, "", 1) != 1)
+		return 1;
+
+	while (read(STDIN_FILENO, &c, 1) > 0)
+		continue;
+
+	return EXEC_STATUS;
+}
+
+/* Copy the binary of this test to a new file at @path. */
+static int copy_self(const char *path)
+{
+	static char buf[65536];
+	int in_fd, out_fd;
+	ssize_t len;
+
+	in_fd = open("/proc/self/exe", O_RDONLY);
+	CHECK(in_fd >= 0);
+	out_fd = open(path, O_CREAT | O_EXCL | O_WRONLY, 0755);
+	CHECK(out_fd >= 0);
+
+	while ((len = read(in_fd, buf, sizeof(buf))) > 0)
+		CHECK_EQ(write(out_fd, buf, len), len);
+	CHECK_EQ(len, 0);
+
+	close(out_fd);
+	close(in_fd);
+	return KSFT_PASS;
+}
+
+/* Return the number of pages of the binary of this test. */
+static long self_pages(void)
+{
+	struct stat st;
+
+	if (stat("/proc/self/exe", &st))
+		return -1;
+
+	return nr_pages(st.st_size);
+}
+
+/* Check that @fd has the contents of the binary of this test. */
+static int check_self(int fd)
+{
+	long long size = file_size(fd);
+	void *p, *self;
+	int self_fd;
+
+	self_fd = open("/proc/self/exe", O_RDONLY);
+	CHECK(self_fd >= 0);
+	CHECK(size > 0);
+	CHECK_EQ(file_size(self_fd), size);
+
+	p = mmap(NULL, size, PROT_READ, MAP_SHARED, fd, 0);
+	CHECK(p != MAP_FAILED);
+	self = mmap(NULL, size, PROT_READ, MAP_SHARED, self_fd, 0);
+	CHECK(self != MAP_FAILED);
+	CHECK(!memcmp(p, self, size));
+
+	munmap(self, size);
+	munmap(p, size);
+	close(self_fd);
+	return KSFT_PASS;
+}
+
+/*
+ * Execute the copy of this test at @path and wait until it runs. Return the
+ * write end of its stdin, which ends it when closed, or -errno if it can't be
+ * executed.
+ */
+static int start_exe(const char *path, pid_t *pid)
+{
+	char *const argv[] = { (char *)path, EXEC_ARG, NULL };
+	char *const envp[] = { NULL };
+	unsigned char err = EIO;
+	int in[2], out[2], status;
+
+	if (pipe2(in, O_CLOEXEC) || pipe2(out, O_CLOEXEC))
+		return -errno;
+
+	fflush(stdout);
+	*pid = fork();
+	if (!*pid) {
+		if (dup2(in[0], STDIN_FILENO) >= 0 &&
+		    dup2(out[1], STDOUT_FILENO) >= 0)
+			execve(path, argv, envp);
+
+		/* Report the error instead of the 0 byte from exec_main(). */
+		err = errno;
+		if (write(out[1], &err, 1) != 1)
+			_exit(2);
+		_exit(1);
+	}
+
+	close(in[0]);
+	close(out[1]);
+	if (*pid > 0 && read(out[0], &err, 1) != 1)
+		err = EIO;
+	close(out[0]);
+	if (!err)
+		return in[1];
+
+	close(in[1]);
+	if (*pid > 0)
+		waitpid(*pid, &status, 0);
+	return -err;
+}
+
+/* End a program started by start_exe() and check its exit status. */
+static int stop_exe(pid_t pid, int stdin_fd)
+{
+	int status;
+
+	close(stdin_fd);
+	CHECK_EQ(waitpid(pid, &status, 0), pid);
+	CHECK(WIFEXITED(status));
+	CHECK_EQ(WEXITSTATUS(status), EXEC_STATUS);
+	return KSFT_PASS;
+}
+
+/* Execute the copy of this test at @path. Return 0 or -errno. */
+static int run_exe(const char *path)
+{
+	pid_t pid = -1;
+	int stdin_fd;
+
+	stdin_fd = start_exe(path, &pid);
+	if (stdin_fd < 0)
+		return stdin_fd;
+
+	return stop_exe(pid, stdin_fd) == KSFT_PASS ? 0 : -ECHILD;
+}
+
+/*
+ * Preserve a copy of the binary of this test while it runs, through a
+ * read-only fd, since it can't be opened for writing.
+ */
+static int preserve_running_exe(struct test_case *tc)
+{
+	int fd, stdin_fd;
+	char path[128];
+	pid_t pid;
+
+	snprintf(path, sizeof(path), "src/%s", tc->name);
+	TRY(copy_self(path));
+
+	stdin_fd = start_exe(path, &pid);
+	CHECK(stdin_fd >= 0);
+	CHECK_ERRNO(open(path, O_RDWR), ETXTBSY);
+
+	fd = open(path, O_RDONLY);
+	CHECK(fd >= 0);
+	CHECK_EQ(luo_session_preserve_fd(session_fd, fd, tc->token), 0);
+	close(fd);
+
+	return stop_exe(pid, stdin_fd);
+}
+
+/* Retrieve the file of @tc onto a new mount at dst, and check it. */
+static int restore_verify(struct test_case *tc)
+{
+	int fd;
+
+	CHECK_EQ(mount_tmpfs("dst", 16, NULL), 0);
+	fd = retrieve_at(tc->token, "dst", O_RDWR, 0644);
+	CHECK(fd >= 0);
+	TRY(check_restored(tc, fd));
+
+	close(fd);
+	return KSFT_PASS;
+}
+
+static int basic_verify(struct test_case *tc)
+{
+	struct stat st, path_st;
+	int fd, path_fd;
+
+	CHECK_EQ(mount_tmpfs("dst", 16, NULL), 0);
+	fd = retrieve_at(tc->token, "dst", O_RDWR, 0666);
+	CHECK(fd >= 0);
+	TRY(check_restored(tc, fd));
+	CHECK_EQ(mnt_used("dst"), nr_pages(tc->size));
+
+	/* The file is created like with open(O_TMPFILE). */
+	CHECK(!fstat(fd, &st));
+	CHECK_EQ(st.st_mode & 07777, 0666 & ~TEST_UMASK);
+	CHECK(S_ISREG(st.st_mode));
+	CHECK_EQ(st.st_nlink, 0);
+	CHECK_EQ(st.st_uid, 0);
+	CHECK_EQ(st.st_gid, 0);
+	CHECK_EQ(do_fcntl(fd, F_GETFL, 0) & (O_ACCMODE | O_TMPFILE),
+		 O_RDWR | O_TMPFILE);
+	CHECK_EQ(do_fcntl(fd, F_GETFD, 0), FD_CLOEXEC);
+
+	/* Like all tmpfs files, the source had F_SEAL_SEAL. */
+	CHECK_EQ(do_fcntl(fd, F_GET_SEALS, 0), F_SEAL_SEAL);
+
+	/* The file can be linked into place, and opened by its path. */
+	CHECK_EQ(link_fd(fd, "dst/f"), 0);
+	CHECK(!stat("dst/f", &path_st));
+	CHECK_EQ(path_st.st_ino, st.st_ino);
+	CHECK_EQ(path_st.st_nlink, 1);
+	path_fd = open("dst/f", O_RDONLY);
+	CHECK(path_fd >= 0);
+	TRY(check_contents(path_fd, tc->size, tc->token));
+	CHECK_EQ(mnt_used("dst"), nr_pages(tc->size));
+
+	close(path_fd);
+	close(fd);
+	return KSFT_PASS;
+}
+
+static int empty_verify(struct test_case *tc)
+{
+	int fd;
+
+	CHECK_EQ(mount_tmpfs("dst", 1, NULL), 0);
+	fd = retrieve_at(tc->token, "dst", O_RDWR, 0644);
+	CHECK(fd >= 0);
+	TRY(check_restored(tc, fd));
+	CHECK_EQ(mnt_used("dst"), 0);
+
+	close(fd);
+	return KSFT_PASS;
+}
+
+static int sparse_preserve(struct test_case *tc)
+{
+	size_t size = SPARSE_PAGES * page_size;
+	int fd;
+
+	/* Only the first and the last page have data. */
+	fd = open("src/sparse", O_CREAT | O_EXCL | O_RDWR, 0644);
+	CHECK(fd >= 0);
+	CHECK_EQ(ftruncate(fd, size), 0);
+	CHECK_EQ(write_pattern(fd, 0, page_size, tc->token), 0);
+	CHECK_EQ(write_pattern(fd, size - page_size, page_size, tc->token), 0);
+	CHECK_EQ(file_pages(fd), 2);
+
+	CHECK_EQ(lseek(fd, 0, SEEK_SET), 0);
+	CHECK_EQ(luo_session_preserve_fd(session_fd, fd, tc->token), 0);
+
+	/* Preserving the file fills the holes. */
+	CHECK_EQ(file_pages(fd), SPARSE_PAGES);
+
+	close(fd);
+	return KSFT_PASS;
+}
+
+static int sparse_verify(struct test_case *tc)
+{
+	size_t size = SPARSE_PAGES * page_size;
+	unsigned char *p;
+	bool data;
+	int fd, i;
+
+	CHECK_EQ(mount_tmpfs("dst", SPARSE_PAGES, NULL), 0);
+	fd = retrieve_at(tc->token, "dst", O_RDWR, 0644);
+	CHECK(fd >= 0);
+	CHECK_EQ(file_size(fd), size);
+	CHECK_EQ(file_pages(fd), SPARSE_PAGES);
+	CHECK_EQ(mnt_used("dst"), SPARSE_PAGES);
+
+	/* The holes read as zeroes. */
+	p = mmap(NULL, size, PROT_READ, MAP_SHARED, fd, 0);
+	CHECK(p != MAP_FAILED);
+	for (i = 0; i < SPARSE_PAGES; i++) {
+		data = i == 0 || i == SPARSE_PAGES - 1;
+		TRY(check_range(p, i * page_size, (i + 1) * page_size,
+				data ? tc->token : 0));
+	}
+
+	munmap(p, size);
+	close(fd);
+	return KSFT_PASS;
+}
+
+static int tmpfile_source_preserve(struct test_case *tc)
+{
+	int fd, ret;
+
+	/* An unlinked tmpfs file is still a tmpfs file. */
+	fd = open("src", O_TMPFILE | O_RDWR, 0644);
+	CHECK(fd >= 0);
+	CHECK_EQ(write_pattern(fd, 0, tc->size, tc->token), 0);
+	ret = preserve_fd(fd, tc->pos, tc->token);
+	close(fd);
+
+	return ret;
+}
+
+static int rdonly_source_preserve(struct test_case *tc)
+{
+	int fd, ret;
+
+	fd = create_source("src/rdonly_source", tc->size, tc->token);
+	CHECK(fd >= 0);
+	close(fd);
+
+	fd = open("src/rdonly_source", O_RDONLY);
+	CHECK(fd >= 0);
+	ret = preserve_fd(fd, tc->pos, tc->token);
+	close(fd);
+
+	return ret;
+}
+
+/* Create a sparse file at @path, with a hole after the first page. */
+static int create_sparse_source(const char *path, __u64 token)
+{
+	int fd;
+
+	fd = create_source(path, page_size, token);
+	if (fd < 0)
+		return -1;
+
+	if (ftruncate(fd, 2 * page_size)) {
+		close(fd);
+		return -1;
+	}
+
+	return fd;
+}
+
+/* Open @path with O_RDONLY and try to preserve it with @token. */
+static int try_preserve_path(const char *path, __u64 token)
+{
+	int fd, ret;
+
+	fd = open(path, O_RDONLY);
+	if (fd < 0)
+		return -errno;
+
+	ret = luo_session_preserve_fd(session_fd, fd, token);
+	close(fd);
+	return ret;
+}
+
+/* Check that the file preserved with @token has the source of @tc. */
+static int check_preserved(struct test_case *tc, __u64 token, size_t size)
+{
+	int fd;
+
+	fd = retrieve_at(token, "dst", O_RDWR, 0644);
+	CHECK(fd >= 0);
+	CHECK_EQ(file_size(fd), size);
+	TRY(check_contents(fd, size, tc->token));
+
+	close(fd);
+	return KSFT_PASS;
+}
+
+/* Check that the file preserved with @token is a create_sparse_source(). */
+static int check_sparse_preserved(struct test_case *tc, __u64 token)
+{
+	unsigned char *p;
+	int fd;
+
+	fd = retrieve_at(token, "dst", O_RDWR, 0644);
+	CHECK(fd >= 0);
+	CHECK_EQ(file_size(fd), 2 * page_size);
+
+	/* Preserving the file filled the hole. */
+	CHECK_EQ(file_pages(fd), 2);
+	p = mmap(NULL, 2 * page_size, PROT_READ, MAP_SHARED, fd, 0);
+	CHECK(p != MAP_FAILED);
+	TRY(check_range(p, 0, page_size, tc->token));
+	TRY(check_range(p, page_size, 2 * page_size, 0));
+
+	munmap(p, 2 * page_size);
+	close(fd);
+	return KSFT_PASS;
+}
+
+static int unwritable_source_child(struct test_case *tc)
+{
+	TRY(drop_privileges());
+
+	/* Preserving a file freezes its size, so it needs write permission. */
+	CHECK_EQ(try_preserve_path("src/unwritable_source", tc->token),
+		 -EACCES);
+	return KSFT_PASS;
+}
+
+static int unwritable_source_preserve(struct test_case *tc)
+{
+	int fd;
+
+	fd = create_source("src/unwritable_source", tc->size, tc->token);
+	CHECK(fd >= 0);
+	CHECK_EQ(do_fchmod(fd, 0444), 0);
+	close(fd);
+
+	return run_child(unwritable_source_child, tc);
+}
+
+static int unwritable_source_verify(struct test_case *tc)
+{
+	CHECK_EQ(luo_session_retrieve_fd(session_fd, tc->token), -ENOENT);
+	return KSFT_PASS;
+}
+
+static int rdonly_mount_source_preserve(struct test_case *tc)
+{
+	int fd;
+
+	fd = create_source("src/rdonly_mount_source", tc->size, tc->token);
+	CHECK(fd >= 0);
+	close(fd);
+	fd = create_sparse_source("src/rdonly_mount_sparse", tc->token);
+	CHECK(fd >= 0);
+	close(fd);
+
+	CHECK_EQ(mkdir("src_ro", 0755), 0);
+	CHECK_EQ(do_mount("src", "src_ro", NULL, MS_BIND, NULL), 0);
+	CHECK_EQ(do_mount("none", "src_ro", NULL,
+			  MS_REMOUNT | MS_BIND | MS_RDONLY, NULL), 0);
+
+	/*
+	 * Files can be preserved through a read-only mount. Their holes are
+	 * filled like by read faults, which work through read-only mounts too.
+	 */
+	CHECK_EQ(try_preserve_path("src_ro/rdonly_mount_source", tc->token), 0);
+	CHECK_EQ(try_preserve_path("src_ro/rdonly_mount_sparse", tc->token + 1),
+		 0);
+	return KSFT_PASS;
+}
+
+static int rdonly_mount_source_verify(struct test_case *tc)
+{
+	CHECK_EQ(mount_tmpfs("dst", 16, NULL), 0);
+	TRY(check_preserved(tc, tc->token, tc->size));
+	TRY(check_sparse_preserved(tc, tc->token + 1));
+	return KSFT_PASS;
+}
+
+static int rdonly_sb_source_child(struct test_case *tc)
+{
+	TRY(drop_privileges());
+
+	/* The owner can preserve a file whose size can't change anyway... */
+	CHECK_EQ(try_preserve_path("src_rosb/own", tc->token + 1), 0);
+
+	/* ... but nobody else can. */
+	CHECK_EQ(try_preserve_path("src_rosb/other", tc->token + 2), -EROFS);
+	return KSFT_PASS;
+}
+
+static int rdonly_sb_source_preserve(struct test_case *tc)
+{
+	int fd;
+
+	CHECK_EQ(mount_tmpfs("src_rosb", 16, NULL), 0);
+	fd = create_source("src_rosb/root", tc->size, tc->token);
+	CHECK(fd >= 0);
+	close(fd);
+	fd = create_source("src_rosb/own", tc->size, tc->token);
+	CHECK(fd >= 0);
+	close(fd);
+	CHECK_EQ(chown("src_rosb/own", NOBODY, NOBODY), 0);
+	fd = create_source("src_rosb/other", tc->size, tc->token);
+	CHECK(fd >= 0);
+	close(fd);
+	fd = create_sparse_source("src_rosb/sparse", tc->token);
+	CHECK(fd >= 0);
+	close(fd);
+
+	CHECK_EQ(do_mount(NULL, "src_rosb", NULL, MS_REMOUNT | MS_RDONLY, NULL),
+		 0);
+
+	CHECK_EQ(try_preserve_path("src_rosb/root", tc->token), 0);
+	TRY(run_child(rdonly_sb_source_child, tc));
+
+	/* Holes are filled like by read faults, also on a read-only superblock. */
+	CHECK_EQ(try_preserve_path("src_rosb/sparse", tc->token + 3), 0);
+	return KSFT_PASS;
+}
+
+static int rdonly_sb_source_verify(struct test_case *tc)
+{
+	CHECK_EQ(mount_tmpfs("dst", 16, NULL), 0);
+	TRY(check_preserved(tc, tc->token, tc->size));
+	TRY(check_preserved(tc, tc->token + 1, tc->size));
+	CHECK_EQ(luo_session_retrieve_fd(session_fd, tc->token + 2), -ENOENT);
+	TRY(check_sparse_preserved(tc, tc->token + 3));
+	return KSFT_PASS;
+}
+
+static int set_immutable(const char *path)
+{
+	int fd, flags, ret = 0;
+
+	fd = open(path, O_RDONLY);
+	if (fd < 0)
+		return -errno;
+
+	if (ioctl(fd, FS_IOC_GETFLAGS, &flags)) {
+		ret = -errno;
+	} else {
+		flags |= FS_IMMUTABLE_FL;
+		if (ioctl(fd, FS_IOC_SETFLAGS, &flags))
+			ret = -errno;
+	}
+
+	close(fd);
+	return ret;
+}
+
+static int immutable_source_preserve(struct test_case *tc)
+{
+	int fd, ret;
+
+	fd = create_source("src/immutable_source", tc->size, tc->token);
+	CHECK(fd >= 0);
+	close(fd);
+	fd = create_sparse_source("src/immutable_sparse", tc->token);
+	CHECK(fd >= 0);
+	close(fd);
+
+	ret = set_immutable("src/immutable_source");
+	if (ret == -ENOTTY || ret == -EOPNOTSUPP) {
+		ksft_print_msg("%s: FS_IOC_SETFLAGS is not supported\n",
+			       tc->name);
+		return KSFT_SKIP;
+	}
+	CHECK_EQ(ret, 0);
+	CHECK_EQ(set_immutable("src/immutable_sparse"), 0);
+
+	/*
+	 * The size of an immutable file can't change anyway, so its owner can
+	 * preserve it. Its holes are filled like by read faults.
+	 */
+	CHECK_EQ(try_preserve_path("src/immutable_source", tc->token), 0);
+	CHECK_EQ(try_preserve_path("src/immutable_sparse", tc->token + 1), 0);
+	return KSFT_PASS;
+}
+
+static int immutable_source_verify(struct test_case *tc)
+{
+	int fd;
+
+	CHECK_EQ(mount_tmpfs("dst", 16, NULL), 0);
+	fd = retrieve_at(tc->token, "dst", O_RDWR, 0644);
+	if (fd == -ENOENT)
+		return skip_not_preserved(tc);
+	CHECK(fd >= 0);
+	CHECK_EQ(file_size(fd), tc->size);
+	TRY(check_contents(fd, tc->size, tc->token));
+	close(fd);
+
+	TRY(check_sparse_preserved(tc, tc->token + 1));
+	return KSFT_PASS;
+}
+
+#define FROZEN_OFFSET		100
+#define FROZEN_DATA		"frozen"
+
+static int frozen_source_preserve(struct test_case *tc)
+{
+	size_t len = strlen(FROZEN_DATA);
+	int fd;
+
+	TRY(preserve_file(tc));
+
+	/* The size of a preserved file can't change, also through its path. */
+	fd = open("src/frozen_source", O_RDWR);
+	CHECK(fd >= 0);
+	CHECK_ERRNO(ftruncate(fd, tc->size / 2), EPERM);
+	CHECK_ERRNO(ftruncate(fd, tc->size * 2), EPERM);
+	CHECK_ERRNO(do_fallocate(fd, 0, 0, tc->size * 2), EPERM);
+	CHECK_ERRNO(do_fallocate(fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
+				 0, page_size), EPERM);
+	CHECK_EQ(lseek(fd, tc->size, SEEK_SET), tc->size);
+	CHECK_ERRNO(write(fd, "x", 1), EPERM);
+	CHECK_EQ(file_size(fd), tc->size);
+
+	/* Writes within the file work, and the data is preserved. */
+	CHECK_EQ(lseek(fd, FROZEN_OFFSET, SEEK_SET), FROZEN_OFFSET);
+	CHECK_EQ(write(fd, FROZEN_DATA, len), len);
+
+	close(fd);
+	return KSFT_PASS;
+}
+
+static int frozen_source_verify(struct test_case *tc)
+{
+	size_t len = strlen(FROZEN_DATA);
+	unsigned char *p;
+	int fd;
+
+	CHECK_EQ(mount_tmpfs("dst", 16, NULL), 0);
+	fd = retrieve_at(tc->token, "dst", O_RDWR, 0644);
+	CHECK(fd >= 0);
+	CHECK_EQ(file_size(fd), tc->size);
+
+	p = mmap(NULL, tc->size, PROT_READ, MAP_SHARED, fd, 0);
+	CHECK(p != MAP_FAILED);
+	TRY(check_range(p, 0, FROZEN_OFFSET, tc->token));
+	CHECK(!memcmp(p + FROZEN_OFFSET, FROZEN_DATA, len));
+	TRY(check_range(p, FROZEN_OFFSET + len, tc->size, tc->token));
+
+	munmap(p, tc->size);
+	close(fd);
+	return KSFT_PASS;
+}
+
+static int rdonly_verify(struct test_case *tc)
+{
+	struct stat st;
+	int fd;
+
+	/* Unlike open(O_TMPFILE), the file can be retrieved read-only. */
+	CHECK_EQ(mount_tmpfs("dst", 16, NULL), 0);
+	fd = retrieve_at(tc->token, "dst", O_RDONLY | O_NONBLOCK, 0444);
+	CHECK(fd >= 0);
+	TRY(check_restored(tc, fd));
+	CHECK(!fstat(fd, &st));
+	CHECK_EQ(st.st_mode & 07777, 0444);
+	CHECK_EQ(do_fcntl(fd, F_GETFL, 0) & (O_ACCMODE | O_NONBLOCK | O_TMPFILE),
+		 O_RDONLY | O_NONBLOCK | O_TMPFILE);
+	CHECK_ERRNO(write(fd, "x", 1), EBADF);
+
+	close(fd);
+	return KSFT_PASS;
+}
+
+static int wronly_verify(struct test_case *tc)
+{
+	int fd, rd_fd;
+
+	CHECK_EQ(mount_tmpfs("dst", 16, NULL), 0);
+	fd = retrieve_at(tc->token, "dst", O_WRONLY | O_APPEND, 0644);
+	CHECK(fd >= 0);
+	CHECK_EQ(do_fcntl(fd, F_GETFL, 0) & (O_ACCMODE | O_APPEND),
+		 O_WRONLY | O_APPEND);
+	CHECK_EQ(file_size(fd), tc->size);
+	CHECK_EQ(lseek(fd, 0, SEEK_CUR), tc->pos);
+
+	rd_fd = reopen_fd(fd, O_RDONLY);
+	CHECK(rd_fd >= 0);
+	TRY(check_contents(rd_fd, tc->size, tc->token));
+
+	close(rd_fd);
+	close(fd);
+	return KSFT_PASS;
+}
+
+static int excl_verify(struct test_case *tc)
+{
+	int fd;
+
+	/* Like with open(O_TMPFILE | O_EXCL), the file can't be linked. */
+	CHECK_EQ(mount_tmpfs("dst", 16, NULL), 0);
+	fd = retrieve_at(tc->token, "dst", O_RDWR | O_EXCL, 0644);
+	CHECK(fd >= 0);
+	TRY(check_restored(tc, fd));
+	CHECK_ERRNO(link_fd(fd, "dst/f"), ENOENT);
+
+	close(fd);
+	return KSFT_PASS;
+}
+
+static int unprivileged_child(struct test_case *tc)
+{
+	struct stat st;
+	int fd;
+
+	TRY(drop_privileges());
+
+	/* Creating the file needs permission to write to the directory. */
+	CHECK_EQ(retrieve_at(tc->token, "dst", O_RDWR, 0644), -EACCES);
+
+	/* The file is owned by the caller. */
+	fd = retrieve_at(tc->token, "dst/nobody", O_RDWR, 0640);
+	CHECK(fd >= 0);
+	TRY(check_restored(tc, fd));
+	CHECK(!fstat(fd, &st));
+	CHECK_EQ(st.st_uid, NOBODY);
+	CHECK_EQ(st.st_gid, NOBODY);
+	CHECK_EQ(st.st_mode & 07777, 0640);
+
+	close(fd);
+	return KSFT_PASS;
+}
+
+static int unprivileged_verify(struct test_case *tc)
+{
+	CHECK_EQ(mount_tmpfs("dst", 16, "mode=0755"), 0);
+	CHECK_EQ(mkdir("dst/nobody", 0755), 0);
+	CHECK_EQ(chown("dst/nobody", NOBODY, NOBODY), 0);
+
+	return run_child(unprivileged_child, tc);
+}
+
+static int rdonly_mount_verify(struct test_case *tc)
+{
+	int fd;
+
+	/* Create the file through a read-only bind mount. */
+	CHECK_EQ(mount_tmpfs("dst", 16, NULL), 0);
+	CHECK_EQ(mkdir("ro", 0755), 0);
+	CHECK_EQ(do_mount("dst", "ro", NULL, MS_BIND, NULL), 0);
+	CHECK_EQ(do_mount("none", "ro", NULL, MS_REMOUNT | MS_BIND | MS_RDONLY,
+			  NULL), 0);
+	CHECK_EQ(retrieve_at(tc->token, "ro", O_RDWR, 0644), -EROFS);
+	CHECK_EQ(retrieve_at(tc->token, "ro", O_RDONLY, 0644), -EROFS);
+
+	/* The failure didn't consume the preserved file. */
+	fd = retrieve_at(tc->token, "dst", O_RDWR, 0644);
+	CHECK(fd >= 0);
+	TRY(check_restored(tc, fd));
+
+	close(fd);
+	return KSFT_PASS;
+}
+
+/*
+ * Retrieve the copy of this test preserved by @tc with the access mode
+ * @flags, and link it at dst/exe.
+ */
+static int retrieve_exe(struct test_case *tc, int flags)
+{
+	long pages = self_pages();
+	int fd;
+
+	CHECK(pages > 0);
+	CHECK_EQ(mount_tmpfs("dst", pages, NULL), 0);
+	fd = retrieve_at(tc->token, "dst", flags, 0755);
+	CHECK(fd >= 0);
+	TRY(check_self(fd));
+	CHECK_EQ(mnt_used("dst"), pages);
+	CHECK_EQ(link_fd(fd, "dst/exe"), 0);
+
+	close(fd);
+	return KSFT_PASS;
+}
+
+static int exec_rdonly_verify(struct test_case *tc)
+{
+	TRY(retrieve_exe(tc, O_RDONLY));
+
+	/*
+	 * LUO keeps the file open until the session is finished, but
+	 * read-only, so the binary can be executed right away.
+	 */
+	CHECK_EQ(run_exe("dst/exe"), 0);
+	return KSFT_PASS;
+}
+
+static int exec_rdwr_verify(struct test_case *tc)
+{
+	TRY(retrieve_exe(tc, O_RDWR));
+
+	/*
+	 * LUO keeps the file open for writing until the session is finished,
+	 * so the binary can't be executed before that.
+	 */
+	CHECK_EQ(run_exe("dst/exe"), -ETXTBSY);
+	return KSFT_PASS;
+}
+
+static int exec_rdwr_after_finish(struct test_case *tc)
+{
+	CHECK_EQ(run_exe("dst/exe"), 0);
+	return KSFT_PASS;
+}
+
+static int mount_fits_verify(struct test_case *tc)
+{
+	unsigned long pages = nr_pages(tc->size);
+	int fd;
+
+	/* The file can be retrieved onto a mount it fits exactly. */
+	CHECK_EQ(mount_tmpfs("fit", pages, NULL), 0);
+	fd = retrieve_at(tc->token, "fit", O_RDWR, 0644);
+	CHECK(fd >= 0);
+	TRY(check_restored(tc, fd));
+	CHECK_EQ(mnt_used("fit"), pages);
+	CHECK_EQ(mnt_free("fit"), 0);
+
+	CHECK_EQ(ftruncate(fd, 0), 0);
+	CHECK_EQ(mnt_used("fit"), 0);
+
+	close(fd);
+	return KSFT_PASS;
+}
+
+static int mount_too_small_verify(struct test_case *tc)
+{
+	unsigned long pages = nr_pages(tc->size);
+
+	/* The failure leaves the mount untouched... */
+	CHECK_EQ(mount_tmpfs("small", pages - 1, NULL), 0);
+	CHECK_EQ(retrieve_at(tc->token, "small", O_RDWR, 0644), -ENOSPC);
+	CHECK_EQ(mnt_used("small"), 0);
+
+	/*
+	 * ... but the preserved contents were restored before it was detected,
+	 * so the failure is permanent. Finishing the session frees them.
+	 */
+	CHECK_EQ(mount_tmpfs("big", pages, NULL), 0);
+	CHECK_EQ(retrieve_at(tc->token, "big", O_RDWR, 0644), -ENOSPC);
+	CHECK_EQ(luo_session_retrieve_fd(session_fd, tc->token), -ENOSPC);
+	CHECK_EQ(mnt_used("big"), 0);
+
+	return KSFT_PASS;
+}
+
+static int huge_folios_verify(struct test_case *tc)
+{
+	unsigned long pages = nr_pages(tc->size);
+	int fd;
+
+	CHECK_EQ(mount_tmpfs("dst", pages, "huge=never"), 0);
+	fd = retrieve_at(tc->token, "dst", O_RDWR, 0644);
+	if (fd == -ENOENT)
+		return skip_not_preserved(tc);
+	CHECK(fd >= 0);
+	TRY(check_restored(tc, fd));
+	CHECK_EQ(mnt_used("dst"), pages);
+
+	/* LUO keeps a reference to the file until the session is finished. */
+	close(fd);
+	CHECK_EQ(mnt_used("dst"), pages);
+
+	return KSFT_PASS;
+}
+
+static int huge_folios_after_finish(struct test_case *tc)
+{
+	CHECK_EQ(mnt_used("dst"), 0);
+	return KSFT_PASS;
+}
+
+static int huge_folio_tail_verify(struct test_case *tc)
+{
+	long pages;
+	int fd;
+
+	CHECK_EQ(mount_tmpfs("dst", 4096, "huge=never"), 0);
+	fd = retrieve_at(tc->token, "dst", O_RDWR, 0644);
+	if (fd == -ENOENT)
+		return skip_not_preserved(tc);
+	CHECK(fd >= 0);
+	CHECK_EQ(file_size(fd), tc->size);
+	CHECK_EQ(lseek(fd, 0, SEEK_CUR), tc->pos);
+	TRY(check_contents(fd, tc->size, tc->token));
+
+	/* The whole folio is charged, including the part past EOF. */
+	pages = file_pages(fd);
+	CHECK(pages > 1);
+	CHECK_EQ(mnt_used("dst"), pages);
+
+	CHECK_EQ(ftruncate(fd, 0), 0);
+	CHECK_EQ(mnt_used("dst"), 0);
+
+	close(fd);
+	return KSFT_PASS;
+}
+
+static int huge_folio_tail_enospc_verify(struct test_case *tc)
+{
+	int ret;
+
+	/* There is room for the file, but not for its last folio. */
+	CHECK_EQ(mount_tmpfs("small", 1, "huge=never"), 0);
+	ret = retrieve_at(tc->token, "small", O_RDWR, 0644);
+	if (ret == -ENOENT)
+		return skip_not_preserved(tc);
+	CHECK_EQ(ret, -ENOSPC);
+	CHECK_EQ(mnt_used("small"), 0);
+
+	return KSFT_PASS;
+}
+
+static int memcg_limit_child(struct test_case *tc)
+{
+	long limit = tc->size / 2, usage;
+	int ret;
+
+	/*
+	 * Don't let the memcg OOM killer kill the child if the folios are not
+	 * large. Large folios are charged without invoking it anyway.
+	 */
+	CHECK_EQ(write_file("/proc/self/oom_score_adj", "-1000"), 0);
+	CHECK_EQ(write_file("memcg/small/cgroup.procs", "0"), 0);
+
+	/* The folios are charged to the memcg of the caller, which is full. */
+	ret = retrieve_at(tc->token, "dst", O_RDWR, 0644);
+	if (ret == -ENOENT)
+		return skip_not_preserved(tc);
+	CHECK_EQ(ret, -ENOMEM);
+
+	/* The failure leaves the mount and the memcg untouched. */
+	CHECK_EQ(mnt_used("dst"), 0);
+	usage = read_long("memcg/small/memory.current");
+	CHECK(usage >= 0 && usage < limit);
+
+	return KSFT_PASS;
+}
+
+static int memcg_limit_verify(struct test_case *tc)
+{
+	unsigned long pages = nr_pages(tc->size);
+	char limit[32];
+	int ret;
+
+	CHECK_EQ(mkdir("memcg", 0755), 0);
+	if (do_mount("cgroup2", "memcg", "cgroup2", 0, NULL)) {
+		ksft_print_msg("%s: cgroup2 is not available\n", tc->name);
+		return KSFT_SKIP;
+	}
+	if (write_file("memcg/cgroup.subtree_control", "+memory")) {
+		ksft_print_msg("%s: The memory controller is not available\n",
+			       tc->name);
+		return KSFT_SKIP;
+	}
+
+	/* A memcg without room for the file. */
+	CHECK_EQ(mkdir("memcg/small", 0755), 0);
+	snprintf(limit, sizeof(limit), "%zu", tc->size * 3 / 4);
+	CHECK_EQ(write_file("memcg/small/memory.max", limit), 0);
+	CHECK_EQ(mount_tmpfs("dst", pages, "huge=never"), 0);
+
+	ret = run_child(memcg_limit_child, tc);
+	rmdir("memcg/small");
+	if (ret != KSFT_PASS)
+		return ret;
+
+	/* The preserved contents were restored, so the failure is permanent. */
+	CHECK_EQ(retrieve_at(tc->token, "dst", O_RDWR, 0644), -ENOMEM);
+	CHECK_EQ(mnt_used("dst"), 0);
+
+	return KSFT_PASS;
+}
+
+static int bad_args_verify(struct test_case *tc)
+{
+	struct {
+		struct liveupdate_shmem_retrieve_arg arg;
+		__u64 extra;
+	} big = {};
+	struct liveupdate_shmem_retrieve_arg arg;
+	int dir_fd, fd;
+
+	CHECK_EQ(mount_tmpfs("dst", 16, NULL), 0);
+	dir_fd = open("dst", O_RDONLY | O_DIRECTORY);
+	CHECK(dir_fd >= 0);
+
+	/* Files from tmpfs mounts are only retrieved onto tmpfs mounts. */
+	CHECK_EQ(luo_session_retrieve_fd(session_fd, tc->token), -EINVAL);
+
+	memset(&arg, 0, sizeof(arg));
+	arg.size = sizeof(arg);
+	arg.dirfd = dir_fd;
+	arg.flags = O_RDWR;
+	arg.mode = 0644;
+
+	/* Problems with the argument itself. */
+	arg.size = offsetof(struct liveupdate_shmem_retrieve_arg, mode);
+	CHECK_EQ(retrieve_arg(tc->token, &arg), -EINVAL);
+	arg.size = 2 * page_size;
+	CHECK_EQ(retrieve_arg(tc->token, &arg), -E2BIG);
+	arg.size = sizeof(arg);
+
+	big.arg = arg;
+	big.arg.size = sizeof(big);
+	big.extra = 1;
+	CHECK_EQ(retrieve_arg(tc->token, &big.arg), -E2BIG);
+
+	/* Like openat2(), unknown flags fail, and so does O_PATH. */
+	arg.flags = O_RDWR | (1ULL << 32);
+	CHECK_EQ(retrieve_arg(tc->token, &arg), -EINVAL);
+	arg.flags = O_PATH;
+	CHECK_EQ(retrieve_arg(tc->token, &arg), -EINVAL);
+
+	/* Flags are checked like for open(O_TMPFILE). */
+	arg.flags = O_RDWR | O_CREAT;
+	CHECK_EQ(retrieve_arg(tc->token, &arg), -EINVAL);
+	arg.flags = O_RDWR;
+
+	arg.mode = 010644;
+	CHECK_EQ(retrieve_arg(tc->token, &arg), -EINVAL);
+	arg.mode = 0644;
+
+	/* Problems with the directory. */
+	arg.dirfd = -1;
+	CHECK_EQ(retrieve_arg(tc->token, &arg), -EBADF);
+	arg.dirfd = open("/proc", O_RDONLY | O_DIRECTORY);
+	CHECK(arg.dirfd >= 0);
+	CHECK_EQ(retrieve_arg(tc->token, &arg), -EINVAL);
+	close(arg.dirfd);
+	arg.dirfd = dir_fd;
+
+	CHECK_EQ(retrieve_arg(tc->token + 1, &arg), -ENOENT);
+	CHECK_EQ(mnt_used("dst"), 0);
+
+	/* The failures didn't consume the preserved file. */
+	fd = retrieve_arg(tc->token, &arg);
+	CHECK(fd >= 0);
+	TRY(check_restored(tc, fd));
+
+	close(fd);
+	close(dir_fd);
+	return KSFT_PASS;
+}
+
+static int retrieve_twice_verify(struct test_case *tc)
+{
+	struct stat st, new_st;
+	int fd, new_fd;
+
+	CHECK_EQ(mount_tmpfs("dst", 16, NULL), 0);
+	fd = retrieve_at(tc->token, "dst", O_RDWR, 0644);
+	CHECK(fd >= 0);
+	TRY(check_restored(tc, fd));
+
+	/* The argument only applies to the retrieve that restores the file. */
+	CHECK_EQ(retrieve_at(tc->token, "dst", O_RDWR, 0644), -EBUSY);
+
+	/* A plain retrieve returns the same file. */
+	new_fd = luo_session_retrieve_fd(session_fd, tc->token);
+	CHECK(new_fd >= 0);
+	CHECK(!fstat(fd, &st));
+	CHECK(!fstat(new_fd, &new_st));
+	CHECK_EQ(new_st.st_dev, st.st_dev);
+	CHECK_EQ(new_st.st_ino, st.st_ino);
+	CHECK_EQ(lseek(new_fd, 77, SEEK_SET), 77);
+	CHECK_EQ(lseek(fd, 0, SEEK_CUR), 77);
+	CHECK_EQ(mnt_used("dst"), nr_pages(tc->size));
+
+	close(new_fd);
+	close(fd);
+	return KSFT_PASS;
+}
+
+static int memfd_preserve(struct test_case *tc)
+{
+	return preserve_memfd(tc, 0, 0);
+}
+
+static int memfd_verify(struct test_case *tc)
+{
+	struct stat st;
+	int fd;
+
+	/* memfds are only retrieved as memfds. */
+	CHECK_EQ(mount_tmpfs("dst", 16, NULL), 0);
+	CHECK_EQ(retrieve_at(tc->token, "dst", O_RDWR, 0644), -EINVAL);
+	CHECK_EQ(mnt_used("dst"), 0);
+
+	fd = luo_session_retrieve_fd(session_fd, tc->token);
+	CHECK(fd >= 0);
+	TRY(check_restored(tc, fd));
+	CHECK(!fstat(fd, &st));
+	CHECK_EQ(st.st_nlink, 0);
+	CHECK_EQ(do_fcntl(fd, F_GETFL, 0) & O_ACCMODE, O_RDWR);
+
+	close(fd);
+	return KSFT_PASS;
+}
+
+#define MEMFD_SEALS		(F_SEAL_SHRINK | F_SEAL_GROW | F_SEAL_WRITE)
+
+static int sealed_memfd_preserve(struct test_case *tc)
+{
+	return preserve_memfd(tc, MFD_ALLOW_SEALING, MEMFD_SEALS);
+}
+
+static int sealed_memfd_verify(struct test_case *tc)
+{
+	void *p;
+	int fd;
+
+	fd = luo_session_retrieve_fd(session_fd, tc->token);
+	CHECK(fd >= 0);
+	TRY(check_restored(tc, fd));
+	CHECK_EQ(do_fcntl(fd, F_GET_SEALS, 0), MEMFD_SEALS);
+	CHECK_ERRNO(write(fd, "x", 1), EPERM);
+	CHECK_ERRNO(ftruncate(fd, 0), EPERM);
+	p = mmap(NULL, page_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+	CHECK(p == MAP_FAILED && errno == EPERM);
+
+	close(fd);
+	return KSFT_PASS;
+}
+
+static int preserve_nothing(struct test_case *tc)
+{
+	return KSFT_PASS;
+}
+
+static int outgoing_session_verify(struct test_case *tc)
+{
+	struct liveupdate_shmem_retrieve_arg arg = {
+		.size = sizeof(arg),
+		.flags = O_RDWR,
+		.mode = 0644,
+	};
+	int out_fd, source_fd;
+
+	out_fd = luo_create_session(dev_fd, SESSION_NAME "_outgoing_session");
+	CHECK(out_fd >= 0);
+	CHECK_EQ(mount_tmpfs("src", 16, NULL), 0);
+	source_fd = open("src", O_TMPFILE | O_RDWR, 0644);
+	CHECK(source_fd >= 0);
+	CHECK_EQ(luo_session_preserve_fd(out_fd, source_fd, tc->token), 0);
+
+	/* Files can only be retrieved from incoming sessions. */
+	arg.dirfd = open("src", O_PATH | O_DIRECTORY);
+	CHECK(arg.dirfd >= 0);
+	CHECK_EQ(luo_session_retrieve_fd_arg(out_fd, tc->token,
+					     (__u64)(uintptr_t)&arg), -EINVAL);
+
+	close(arg.dirfd);
+	close(source_fd);
+	close(out_fd);
+	return KSFT_PASS;
+}
+
+static struct test_case test_cases[] = {
+	/* The restored file. */
+	{
+		.name = "basic",
+		.size = 10000,
+		.pos = 1234,
+		.verify = basic_verify,
+	},
+	{
+		.name = "empty",
+		.pos = 100,
+		.verify = empty_verify,
+	},
+	{
+		.name = "sparse",
+		.preserve = sparse_preserve,
+		.verify = sparse_verify,
+	},
+	{
+		.name = "tmpfile_source",
+		.size = SMALL_SIZE,
+		.pos = 4000,
+		.preserve = tmpfile_source_preserve,
+		.verify = restore_verify,
+	},
+	{
+		.name = "rdonly_source",
+		.size = SMALL_SIZE,
+		.pos = 300,
+		.preserve = rdonly_source_preserve,
+		.verify = restore_verify,
+	},
+	{
+		.name = "unwritable_source",
+		.size = SMALL_SIZE,
+		.preserve = unwritable_source_preserve,
+		.verify = unwritable_source_verify,
+	},
+	{
+		.name = "rdonly_mount_source",
+		.size = SMALL_SIZE,
+		.preserve = rdonly_mount_source_preserve,
+		.verify = rdonly_mount_source_verify,
+	},
+	{
+		.name = "rdonly_sb_source",
+		.size = SMALL_SIZE,
+		.preserve = rdonly_sb_source_preserve,
+		.verify = rdonly_sb_source_verify,
+	},
+	{
+		.name = "immutable_source",
+		.size = SMALL_SIZE,
+		.preserve = immutable_source_preserve,
+		.verify = immutable_source_verify,
+	},
+	{
+		.name = "frozen_source",
+		.size = SMALL_SIZE,
+		.preserve = frozen_source_preserve,
+		.verify = frozen_source_verify,
+	},
+	/* Creating the file. */
+	{
+		.name = "rdonly",
+		.size = SMALL_SIZE,
+		.pos = 42,
+		.verify = rdonly_verify,
+	},
+	{
+		.name = "wronly",
+		.size = SMALL_SIZE,
+		.pos = 43,
+		.verify = wronly_verify,
+	},
+	{
+		.name = "excl",
+		.size = SMALL_SIZE,
+		.verify = excl_verify,
+	},
+	{
+		.name = "unprivileged",
+		.size = SMALL_SIZE,
+		.verify = unprivileged_verify,
+	},
+	{
+		.name = "rdonly_mount",
+		.size = SMALL_SIZE,
+		.verify = rdonly_mount_verify,
+	},
+	{
+		.name = "exec_rdonly",
+		.preserve = preserve_running_exe,
+		.verify = exec_rdonly_verify,
+	},
+	{
+		.name = "exec_rdwr",
+		.preserve = preserve_running_exe,
+		.verify = exec_rdwr_verify,
+		.after_finish = exec_rdwr_after_finish,
+	},
+	/* Block accounting. */
+	{
+		.name = "mount_fits",
+		.size = 2 << 20,
+		.verify = mount_fits_verify,
+	},
+	{
+		.name = "mount_too_small",
+		.size = 2 << 20,
+		.verify = mount_too_small_verify,
+	},
+	{
+		.name = "huge_folios",
+		.size = 4 << 20,
+		.preserve = preserve_huge_file,
+		.verify = huge_folios_verify,
+		.after_finish = huge_folios_after_finish,
+	},
+	{
+		.name = "huge_folio_tail",
+		.size = 100,
+		.pos = 10,
+		.preserve = preserve_huge_file,
+		.verify = huge_folio_tail_verify,
+	},
+	{
+		.name = "huge_folio_tail_enospc",
+		.size = 100,
+		.preserve = preserve_huge_file,
+		.verify = huge_folio_tail_enospc_verify,
+	},
+	{
+		.name = "memcg_limit",
+		.size = 4 << 20,
+		.preserve = preserve_huge_file,
+		.verify = memcg_limit_verify,
+	},
+	/* memfds. */
+	{
+		.name = "memfd",
+		.size = SMALL_SIZE,
+		.pos = 700,
+		.preserve = memfd_preserve,
+		.verify = memfd_verify,
+	},
+	{
+		.name = "sealed_memfd",
+		.size = SMALL_SIZE,
+		.preserve = sealed_memfd_preserve,
+		.verify = sealed_memfd_verify,
+	},
+	/* Interactions with LUO. */
+	{
+		.name = "bad_args",
+		.size = SMALL_SIZE,
+		.pos = 800,
+		.verify = bad_args_verify,
+	},
+	{
+		.name = "retrieve_twice",
+		.size = SMALL_SIZE,
+		.pos = 500,
+		.verify = retrieve_twice_verify,
+	},
+	{
+		.name = "outgoing_session",
+		.preserve = preserve_nothing,
+		.verify = outgoing_session_verify,
+	},
+};
+
+static long read_taint(void)
+{
+	return read_long("/proc/sys/kernel/tainted");
+}
+
+static int check_taint(long old_taint)
+{
+	long taint = read_taint();
+
+	if (old_taint < 0 || taint < 0) {
+		ksft_print_msg("Failed to read the taint flags\n");
+		return KSFT_SKIP;
+	}
+
+	if (old_taint & BAD_TAINT) {
+		ksft_print_msg("The kernel was already tainted\n");
+		return KSFT_SKIP;
+	}
+
+	CHECK_EQ(taint & BAD_TAINT, 0);
+	return KSFT_PASS;
+}
+
+static void setup(int luo_fd)
+{
+	unsigned int i;
+
+	dev_fd = luo_fd;
+	page_size = getpagesize();
+	umask(TEST_UMASK);
+
+	for (i = 0; i < ARRAY_SIZE(test_cases); i++)
+		test_cases[i].token = (i + 1) * 0x100;
+
+	if (mount_tmpfs(TEST_DIR, 16, "mode=0755"))
+		fail_exit("Failed to mount %s", TEST_DIR);
+}
+
+static void enter_case_dir(struct test_case *tc)
+{
+	char dir[128];
+
+	snprintf(dir, sizeof(dir), TEST_DIR "/%s", tc->name);
+	if ((mkdir(dir, 0755) && errno != EEXIST) || chdir(dir))
+		fail_exit("Failed to create %s", dir);
+}
+
+static void run_stage_1(int luo_fd)
+{
+	long taint = read_taint();
+	struct test_case *tc;
+	unsigned int i;
+	int ret;
+
+	ksft_print_msg("[STAGE 1] Creating state file for next stage (2)...\n");
+	create_state_file(luo_fd, STATE_SESSION_NAME, STATE_TOKEN, 2);
+
+	setup(luo_fd);
+	if (chdir(TEST_DIR) || mount_tmpfs("src", 4096, "huge=never"))
+		fail_exit("Failed to mount the source tmpfs");
+
+	have_huge_src = !mount_tmpfs("src_huge", 4096, "huge=always");
+	if (!have_huge_src)
+		ksft_print_msg("[STAGE 1] huge=always is not supported\n");
+
+	session_fd = luo_create_session(luo_fd, SESSION_NAME);
+	if (session_fd < 0)
+		fail_exit("luo_create_session for '%s'", SESSION_NAME);
+
+	ksft_print_msg("[STAGE 1] Preserving the source files...\n");
+	for (i = 0; i < ARRAY_SIZE(test_cases); i++) {
+		tc = &test_cases[i];
+		ret = tc->preserve ? tc->preserve(tc) : preserve_file(tc);
+		if (ret == KSFT_SKIP)
+			ksft_print_msg("[STAGE 1] %s: Skipped\n", tc->name);
+		else if (ret != KSFT_PASS)
+			ksft_exit_fail_msg("%s: Failed to preserve\n",
+					   tc->name);
+	}
+
+	if (check_taint(taint) == KSFT_FAIL)
+		ksft_exit_fail_msg("The kernel was tainted in stage 1\n");
+
+	close(luo_fd);
+	daemonize_and_wait();
+}
+
+static void run_stage_2(int luo_fd, int state_session_fd)
+{
+	long taint = read_taint();
+	unsigned int i, nr_tests;
+	struct test_case *tc;
+	int stage, ret;
+
+	ksft_print_msg("[STAGE 2] Starting post-kexec verification...\n");
+	restore_and_read_stage(state_session_fd, STATE_TOKEN, &stage);
+	if (stage != 2)
+		fail_exit("Expected stage 2, but state file contains %d",
+			  stage);
+
+	setup(luo_fd);
+	session_fd = luo_retrieve_session(luo_fd, SESSION_NAME);
+	if (session_fd < 0)
+		fail_exit("luo_retrieve_session for '%s'", SESSION_NAME);
+
+	nr_tests = ARRAY_SIZE(test_cases) + 1;
+	for (i = 0; i < ARRAY_SIZE(test_cases); i++)
+		nr_tests += !!test_cases[i].after_finish;
+
+	ksft_print_header();
+	ksft_set_plan(nr_tests);
+
+	for (i = 0; i < ARRAY_SIZE(test_cases); i++) {
+		tc = &test_cases[i];
+		enter_case_dir(tc);
+		tc->result = tc->verify(tc);
+		ksft_test_result_report(tc->result, "%s\n", tc->name);
+	}
+
+	if (luo_session_finish(session_fd))
+		fail_exit("luo_session_finish for '%s'", SESSION_NAME);
+	close(session_fd);
+
+	for (i = 0; i < ARRAY_SIZE(test_cases); i++) {
+		tc = &test_cases[i];
+		if (!tc->after_finish)
+			continue;
+
+		enter_case_dir(tc);
+		ret = KSFT_SKIP;
+		if (tc->result == KSFT_PASS)
+			ret = tc->after_finish(tc);
+		ksft_test_result_report(ret, "%s_after_finish\n", tc->name);
+	}
+
+	if (chdir("/") || syscall(__NR_umount2, TEST_DIR, MNT_DETACH) ||
+	    rmdir(TEST_DIR))
+		fail_exit("Failed to clean up %s", TEST_DIR);
+
+	ksft_test_result_report(check_taint(taint), "no_kernel_warnings\n");
+
+	if (luo_session_finish(state_session_fd))
+		fail_exit("luo_session_finish for state session");
+	close(state_session_fd);
+
+	if (!ksft_get_fail_cnt())
+		ksft_print_msg("--- TMPFS TEST PASSED ---\n");
+
+	ksft_finished();
+}
+
+int main(int argc, char *argv[])
+{
+	if (argc == 2 && !strcmp(argv[1], EXEC_ARG))
+		return exec_main();
+
+	return luo_test(argc, argv, STATE_SESSION_NAME,
+			run_stage_1, run_stage_2);
+}
diff --git a/tools/testing/selftests/liveupdate/run-vmtests.sh b/tools/testing/selftests/liveupdate/run-vmtests.sh
index d656ce58c5a7..2619e72de76d 100755
--- a/tools/testing/selftests/liveupdate/run-vmtests.sh
+++ b/tools/testing/selftests/liveupdate/run-vmtests.sh
@@ -20,6 +20,7 @@ TEST_NAMES=(
 	"luo_multi_session"
 	"luo_stress_files"
 	"luo_stress_sessions"
+	"luo_tmpfs"
 )
 
 function usage() {
-- 
2.56.0.257.gf7497c7d27-goog