[PATCH v4 04/19] liveupdate: Reference struct luo_file_set_ser via serialized pointer

[Tarun Sahu <tarunsahu@google.com>]

struct luo_session_ser currently embeds struct luo_file_set_ser directly
by value. Embedding struct luo_file_set_ser couples the session layout's
size and field offsets to struct luo_file_set_ser, preventing either
structure from appending fields independently across kexec.

Convert struct luo_session_ser to hold a DECLARE_KHOSER_PTR pointer to
struct luo_file_set_ser instead of embedding it by value. Reserve space
for both structures in each session block-set entry, placing struct
luo_file_set_ser immediately after struct luo_session_ser, and bump
LUO_ABI_COMPATIBLE from luo-v5 to luo-v6.

Signed-off-by: Tarun Sahu <tarunsahu@google.com>
---
 include/linux/kho/abi/luo.h     |  9 +++++----
 kernel/liveupdate/luo_session.c | 27 ++++++++++++++++++++++-----
 2 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/include/linux/kho/abi/luo.h b/include/linux/kho/abi/luo.h
index 721949374fa1..f1152470f71a 100644
--- a/include/linux/kho/abi/luo.h
+++ b/include/linux/kho/abi/luo.h
@@ -61,13 +61,14 @@
 #include <linux/build_bug.h>
 #include <linux/kconfig.h>
 #include <linux/kho/abi/block.h>
+#include <linux/kho/abi/kexec_handover.h>
 #include <uapi/linux/liveupdate.h>
 
 /*
  * The LUO state is registered under this KHO entry name.
  */
 #define LUO_KHO_ENTRY_NAME	"LUO"
-#define LUO_ABI_COMPATIBLE	"luo-v5"
+#define LUO_ABI_COMPATIBLE	"luo-v6"
 #define LUO_ABI_COMPAT_LEN	ALIGN(sizeof(LUO_ABI_COMPATIBLE), 8)
 
 /**
@@ -133,7 +134,7 @@ static_assert(!IS_ENABLED(CONFIG_64BIT) ||
  * struct luo_session_ser - Represents the serialized metadata for a LUO session.
  * @name:         The unique name of the session, provided by the userspace at
  *                the time of session creation.
- * @file_set_ser: Serialized files belonging to this session,
+ * @file_set_ser: Serialized pointer to the files belonging to this session.
  *
  * This structure is used to package session-specific metadata for transfer
  * between kernels via Kexec Handover. An array of these structures (one per
@@ -144,10 +145,10 @@ static_assert(!IS_ENABLED(CONFIG_64BIT) ||
  */
 struct luo_session_ser {
 	char name[LIVEUPDATE_SESSION_NAME_LENGTH];
-	struct luo_file_set_ser file_set_ser;
+	DECLARE_KHOSER_PTR(file_set_ser, struct luo_file_set_ser *);
 };
 
-static_assert(sizeof(struct luo_session_ser) == 80);
+static_assert(sizeof(struct luo_session_ser) == 72);
 static_assert(!IS_ENABLED(CONFIG_64BIT) ||
 	      __alignof__(struct luo_session_ser) == 8);
 
diff --git a/kernel/liveupdate/luo_session.c b/kernel/liveupdate/luo_session.c
index 74bc66929f4b..df667fe15fb2 100644
--- a/kernel/liveupdate/luo_session.c
+++ b/kernel/liveupdate/luo_session.c
@@ -131,18 +131,21 @@ struct luo_session_global {
 	struct luo_session_header outgoing;
 };
 
+#define LUO_SESSION_SER_SIZE (sizeof(struct luo_session_ser) + \
+			      sizeof(struct luo_file_set_ser))
+
 static struct luo_session_global luo_session_global = {
 	.incoming = {
 		.list = LIST_HEAD_INIT(luo_session_global.incoming.list),
 		.rwsem = __RWSEM_INITIALIZER(luo_session_global.incoming.rwsem),
 		.block_set = KHO_BLOCK_SET_INIT(luo_session_global.incoming.block_set,
-						sizeof(struct luo_session_ser)),
+						LUO_SESSION_SER_SIZE),
 	},
 	.outgoing = {
 		.list = LIST_HEAD_INIT(luo_session_global.outgoing.list),
 		.rwsem = __RWSEM_INITIALIZER(luo_session_global.outgoing.rwsem),
 		.block_set = KHO_BLOCK_SET_INIT(luo_session_global.outgoing.block_set,
-						sizeof(struct luo_session_ser)),
+						LUO_SESSION_SER_SIZE),
 	},
 };
 
@@ -223,14 +226,16 @@ static void luo_session_unfreeze_one(struct luo_session *session,
 				     struct luo_session_ser *ser)
 {
 	guard(mutex)(&session->mutex);
-	luo_file_unfreeze(&session->file_set, &ser->file_set_ser);
+	luo_file_unfreeze(&session->file_set,
+			  KHOSER_LOAD_PTR(ser->file_set_ser));
 }
 
 static int luo_session_freeze_one(struct luo_session *session,
 				  struct luo_session_ser *ser)
 {
 	guard(mutex)(&session->mutex);
-	return luo_file_freeze(&session->file_set, &ser->file_set_ser);
+	return luo_file_freeze(&session->file_set,
+			       KHOSER_LOAD_PTR(ser->file_set_ser));
 }
 
 static int luo_session_release(struct inode *inodep, struct file *filep)
@@ -552,6 +557,17 @@ int __init luo_session_setup_incoming(u64 sessions_pa)
 	return 0;
 }
 
+static struct luo_session_ser *luo_session_ser_init(void *mem)
+{
+	struct luo_file_set_ser *file_set_ser;
+	struct luo_session_ser *ser = mem;
+
+	file_set_ser = mem + sizeof(struct luo_session_ser);
+	KHOSER_STORE_PTR(ser->file_set_ser, file_set_ser);
+
+	return ser;
+}
+
 static int luo_session_deserialize_one(struct luo_session_header *sh,
 				       struct luo_session_ser *ser)
 {
@@ -575,7 +591,7 @@ static int luo_session_deserialize_one(struct luo_session_header *sh,
 
 	scoped_guard(mutex, &session->mutex) {
 		err = luo_file_deserialize(&session->file_set,
-					   &ser->file_set_ser);
+					   KHOSER_LOAD_PTR(ser->file_set_ser));
 	}
 	if (err) {
 		pr_warn("Failed to deserialize files for session [%s] %pe\n",
@@ -657,6 +673,7 @@ int luo_session_serialize(void)
 			goto err_undo;
 		}
 
+		ser = luo_session_ser_init(ser);
 		err = luo_session_freeze_one(session, ser);
 		if (err) {
 			kho_block_set_it_prev(&it);
-- 
2.56.0.506.g506a7eabc5-goog