* [PATCH v8 1/9] vfio/pci: Remove DMABUF export dependency on vdev->memory_lock
2026-10-06 19:36 [PATCH v8 0/9] vfio/pci: Add mmap() for DMABUFs Matt Evans
@ 2026-10-06 19:36 ` Matt Evans
2026-10-06 19:36 ` [PATCH v8 2/9] vfio/pci: Un-revoke DMABUFs in LOW_POWER_ENTRY_WITH_WAKEUP resume Matt Evans
` (7 subsequent siblings)
8 siblings, 0 replies; 11+ messages in thread
From: Matt Evans @ 2026-10-06 19:36 UTC (permalink / raw)
To: Alex Williamson, Leon Romanovsky, Jason Gunthorpe, Alex Mastro,
Christian König, Kevin Tian, Pranjal Shrivastava,
Longfang Liu
Cc: Mahmoud Adam, David Matlack, Björn Töpel, Sumit Semwal,
Ankit Agrawal, Alistair Popple, Vivek Kasireddy, linux-kernel,
linux-media, dri-devel, linaro-mm-sig, kvm, linux-pci
The VFIO_DEVICE_FEATURE_DMA_BUF export previously used
vdev->memory_lock to protect VFIO's list of exported DMABUFs
(vdev->dmabufs) and their revocation status. When adding a new
export, memory_lock was taken for write.
A future commit will refactor DMABUF export into a function used from
mmap(), which would create a new mmap_lock -> memory_lock dependency.
In preparation, this commit introduces a vdev->dmabuf_lock that
protects the dmabufs list, per-DMABUF revocation state, and a new
bars_revoked flag. The flag tracks the device-wide BAR revocation
state set via vfio_pci_dma_buf_move() under dmabuf_lock, removing the
test of __vfio_pci_memory_enabled() and dependency on
vdev->memory_lock.
This is a cleanup currently, but allows the future export path to
avoid holding memory_lock under mmap_lock and a therefore avoid a
deadlock scenario (a fault handler attempting to take mmap_lock in a
vfio-pci variant driver thread that holds memory_lock, vs another
thread doing an mmap/export holding them both in the other order).
Signed-off-by: Matt Evans <matt@ozlabs.org>
---
drivers/vfio/pci/vfio_pci_core.c | 2 ++
drivers/vfio/pci/vfio_pci_dmabuf.c | 30 +++++++++++++++++++++++++-----
include/linux/vfio_pci_core.h | 2 ++
3 files changed, 29 insertions(+), 5 deletions(-)
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 6757054e9d87..1f6066107831 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -663,6 +663,7 @@ int vfio_pci_core_enable(struct vfio_pci_core_device *vdev)
vdev->has_vga = true;
vfio_pci_core_map_bars(vdev);
+ vdev->bars_revoked = false;
return 0;
@@ -2197,6 +2198,7 @@ int vfio_pci_core_init_dev(struct vfio_device *core_vdev)
return ret;
INIT_LIST_HEAD(&vdev->dmabufs);
init_rwsem(&vdev->memory_lock);
+ init_rwsem(&vdev->dmabuf_lock);
xa_init(&vdev->ctx);
return 0;
diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
index c16f460c01d6..847ee5cc78e7 100644
--- a/drivers/vfio/pci/vfio_pci_dmabuf.c
+++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
@@ -90,9 +90,9 @@ static void vfio_pci_dma_buf_release(struct dma_buf *dmabuf)
* The refcount prevents both.
*/
if (priv->vdev) {
- down_write(&priv->vdev->memory_lock);
+ down_write(&priv->vdev->dmabuf_lock);
list_del_init(&priv->dmabufs_elm);
- up_write(&priv->vdev->memory_lock);
+ up_write(&priv->vdev->dmabuf_lock);
vfio_device_put_registration(&priv->vdev->vdev);
}
kfree(priv->phys_vec);
@@ -305,12 +305,27 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
/* dma_buf_put() now frees priv */
INIT_LIST_HEAD(&priv->dmabufs_elm);
- down_write(&vdev->memory_lock);
+
+ /*
+ * dmabuf_lock synchronises access (R) or updates (W) to the
+ * vdev->dmabufs list and to bars_revoked (see below). The
+ * revocation state of DMABUF elements in the list is written
+ * holding both dmabuf_lock(W) and resv, and tested with
+ * either.
+ *
+ * dmabuf_lock -> resv
+ *
+ * vdev->bars_revoked tracks the BAR revocation status updated
+ * via vfio_pci_dma_buf_move(), so the initial DMABUF state
+ * follows the same criteria that later update the DMABUF
+ * state (BAR zap, etc.).
+ */
+ down_write(&vdev->dmabuf_lock);
dma_resv_lock(priv->dmabuf->resv, NULL);
- priv->revoked = !__vfio_pci_memory_enabled(vdev);
+ priv->revoked = vdev->bars_revoked;
list_add_tail(&priv->dmabufs_elm, &vdev->dmabufs);
dma_resv_unlock(priv->dmabuf->resv);
- up_write(&vdev->memory_lock);
+ up_write(&vdev->dmabuf_lock);
/*
* dma_buf_fd() consumes the reference, when the file closes the dmabuf
@@ -340,6 +355,8 @@ void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked)
lockdep_assert_held_write(&vdev->memory_lock);
+ down_write(&vdev->dmabuf_lock);
+ vdev->bars_revoked = revoked;
list_for_each_entry_safe(priv, tmp, &vdev->dmabufs, dmabufs_elm) {
if (!get_file_active(&priv->dmabuf->file))
continue;
@@ -375,6 +392,7 @@ void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked)
}
fput(priv->dmabuf->file);
}
+ up_write(&vdev->dmabuf_lock);
}
void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev)
@@ -393,6 +411,7 @@ void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev)
*/
vfio_pci_dma_buf_move(vdev, true);
+ down_write(&vdev->dmabuf_lock);
list_for_each_entry_safe(priv, tmp, &vdev->dmabufs, dmabufs_elm) {
if (!get_file_active(&priv->dmabuf->file))
continue;
@@ -402,5 +421,6 @@ void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev)
vfio_device_put_registration(&vdev->vdev);
fput(priv->dmabuf->file);
}
+ up_write(&vdev->dmabuf_lock);
up_write(&vdev->memory_lock);
}
diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
index 9a1674c152aa..f99b152edcca 100644
--- a/include/linux/vfio_pci_core.h
+++ b/include/linux/vfio_pci_core.h
@@ -134,6 +134,7 @@ struct vfio_pci_core_device {
bool pm_intx_masked;
bool pm_runtime_engaged;
bool sriov_active;
+ bool bars_revoked;
struct pci_saved_state *pci_saved_state;
struct pci_saved_state *pm_save;
int ioeventfds_nr;
@@ -148,6 +149,7 @@ struct vfio_pci_core_device {
struct vfio_pci_core_device *sriov_pf_core_dev;
struct notifier_block nb;
struct rw_semaphore memory_lock;
+ struct rw_semaphore dmabuf_lock;
struct list_head dmabufs;
};
--
2.47.3
^ permalink raw reply [flat|nested] 11+ messages in thread* [PATCH v8 2/9] vfio/pci: Un-revoke DMABUFs in LOW_POWER_ENTRY_WITH_WAKEUP resume
2026-10-06 19:36 [PATCH v8 0/9] vfio/pci: Add mmap() for DMABUFs Matt Evans
2026-10-06 19:36 ` [PATCH v8 1/9] vfio/pci: Remove DMABUF export dependency on vdev->memory_lock Matt Evans
@ 2026-10-06 19:36 ` Matt Evans
2026-10-06 19:36 ` [PATCH v8 3/9] dma-buf: Provide dma_buf_set_name() Matt Evans
` (6 subsequent siblings)
8 siblings, 0 replies; 11+ messages in thread
From: Matt Evans @ 2026-10-06 19:36 UTC (permalink / raw)
To: Alex Williamson, Leon Romanovsky, Jason Gunthorpe, Alex Mastro,
Christian König, Kevin Tian, Pranjal Shrivastava,
Longfang Liu
Cc: Mahmoud Adam, David Matlack, Björn Töpel, Sumit Semwal,
Ankit Agrawal, Alistair Popple, Vivek Kasireddy, linux-kernel,
linux-media, dri-devel, linaro-mm-sig, kvm, linux-pci
VFIO_DEVICE_FEATURE_LOW_POWER_ENTRY_WITH_WAKEUP correctly revokes
DMABUFs on entry and, when paired with a
VFIO_DEVICE_FEATURE_LOW_POWER_EXIT, vfio_pci_runtime_pm_exit()
correctly un-revokes them.
However, when vfio_pci_core_runtime_resume() signals the eventfd on
resume, the bare __vfio_pci_runtime_pm_exit() is used (which does not
un-revoke). Add vfio_pci_dma_buf_move(false) to the resume path,
making it similar to vfio_pci_runtime_pm_exit().
This also reorders the eventfd signal after the un-revoke and
__vfio_pci_runtime_pm_exit() to guarantee that woken threads observe
the new state.
Fixes: 5d74781ebc86 ("vfio/pci: Add dma-buf export support for MMIO regions")
Signed-off-by: Matt Evans <matt@ozlabs.org>
---
drivers/vfio/pci/vfio_pci_core.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 1f6066107831..e170cdc7ac92 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -527,8 +527,14 @@ static int vfio_pci_core_runtime_resume(struct device *dev)
*/
down_write(&vdev->memory_lock);
if (vdev->pm_wake_eventfd_ctx) {
- eventfd_signal(vdev->pm_wake_eventfd_ctx);
+ struct eventfd_ctx *ctx = vdev->pm_wake_eventfd_ctx;
+
+ vdev->pm_wake_eventfd_ctx = NULL;
__vfio_pci_runtime_pm_exit(vdev);
+ if (__vfio_pci_memory_enabled(vdev))
+ vfio_pci_dma_buf_move(vdev, false);
+ eventfd_signal(ctx);
+ eventfd_ctx_put(ctx);
}
up_write(&vdev->memory_lock);
--
2.47.3
^ permalink raw reply [flat|nested] 11+ messages in thread* [PATCH v8 3/9] dma-buf: Provide dma_buf_set_name()
2026-10-06 19:36 [PATCH v8 0/9] vfio/pci: Add mmap() for DMABUFs Matt Evans
2026-10-06 19:36 ` [PATCH v8 1/9] vfio/pci: Remove DMABUF export dependency on vdev->memory_lock Matt Evans
2026-10-06 19:36 ` [PATCH v8 2/9] vfio/pci: Un-revoke DMABUFs in LOW_POWER_ENTRY_WITH_WAKEUP resume Matt Evans
@ 2026-10-06 19:36 ` Matt Evans
2026-10-07 9:22 ` Christian König
2026-10-06 19:36 ` [PATCH v8 4/9] vfio/pci: Add a helper to look up PFNs for DMABUFs Matt Evans
` (5 subsequent siblings)
8 siblings, 1 reply; 11+ messages in thread
From: Matt Evans @ 2026-10-06 19:36 UTC (permalink / raw)
To: Alex Williamson, Leon Romanovsky, Jason Gunthorpe, Alex Mastro,
Christian König, Kevin Tian, Pranjal Shrivastava,
Longfang Liu
Cc: Mahmoud Adam, David Matlack, Björn Töpel, Sumit Semwal,
Ankit Agrawal, Alistair Popple, Vivek Kasireddy, linux-kernel,
linux-media, dri-devel, linaro-mm-sig, kvm, linux-pci
Allow exporters to set the name of buffers, during export or for
subsequent updates. This is useful to express buffer-specific debug
information, indicate state particular to the exporter's usage, etc.
Only exporters and userspace are expected to set names; it isn't
sensible for importers to do it.
Originally, the static dma_buf_set_name() was used for
DMA_BUF_SET_NAME ioctls, taking a __user string parameter. Export
this function as a generic set-name helper, taking a kernel-allocated
string. The SET_NAME ioctls now locally duplicate the __user string,
and use the new function to set the name.
Signed-off-by: Matt Evans <matt@ozlabs.org>
---
drivers/dma-buf/dma-buf.c | 84 +++++++++++++++++++++++++--------------
include/linux/dma-buf.h | 16 +++++---
2 files changed, 64 insertions(+), 36 deletions(-)
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 4c9add51f9ef..b99da4ff2ef6 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -404,34 +404,6 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
return events;
}
-/**
- * dma_buf_set_name - Set a name to a specific dma_buf to track the usage.
- * It could support changing the name of the dma-buf if the same
- * piece of memory is used for multiple purpose between different devices.
- *
- * @dmabuf: [in] dmabuf buffer that will be renamed.
- * @buf: [in] A piece of userspace memory that contains the name of
- * the dma-buf.
- *
- * Returns 0 on success. If the dma-buf buffer is already attached to
- * devices, return -EBUSY.
- *
- */
-static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf)
-{
- char *name = strndup_user(buf, DMA_BUF_NAME_LEN);
-
- if (IS_ERR(name))
- return PTR_ERR(name);
-
- spin_lock(&dmabuf->name_lock);
- kfree(dmabuf->name);
- dmabuf->name = name;
- spin_unlock(&dmabuf->name_lock);
-
- return 0;
-}
-
#if IS_ENABLED(CONFIG_SYNC_FILE)
static long dma_buf_export_sync_file(struct dma_buf *dmabuf,
void __user *user_data)
@@ -577,8 +549,19 @@ static long dma_buf_ioctl(struct file *file,
return ret;
case DMA_BUF_SET_NAME_A:
- case DMA_BUF_SET_NAME_B:
- return dma_buf_set_name(dmabuf, (const char __user *)arg);
+ case DMA_BUF_SET_NAME_B: {
+ char *name = strndup_user((const char __user *)arg,
+ DMA_BUF_NAME_LEN);
+
+ if (IS_ERR(name))
+ return PTR_ERR(name);
+
+ ret = dma_buf_set_name(dmabuf, name);
+ if (ret)
+ kfree(name);
+
+ return ret;
+ }
#if IS_ENABLED(CONFIG_SYNC_FILE)
case DMA_BUF_IOCTL_EXPORT_SYNC_FILE:
@@ -874,6 +857,42 @@ void dma_buf_put(struct dma_buf *dmabuf)
}
EXPORT_SYMBOL_NS_GPL(dma_buf_put, "DMA_BUF");
+/**
+ * dma_buf_set_name - Set a dmabuf's name
+ * @dmabuf: [in] dmabuf buffer that will be renamed.
+ * @name: [in] The name of the dma-buf, allocated with kmalloc() or
+ * similar. This takes ownership of the allocation
+ * on success, which will be kfree()d when the
+ * dmabuf is released or a new name assigned.
+ *
+ * Intended to be used by the exporter to set a name for debug
+ * purposes. This can also change an existing name if the same piece
+ * of memory is used for multiple purposes over time. Importers
+ * should NOT use this function to overwrite the name.
+ *
+ * Return: 0 on success, -EINVAL if the name is NULL, or -E2BIG if the
+ * name (including terminator) exceeds DMA_BUF_NAME_LEN.
+ */
+int dma_buf_set_name(struct dma_buf *dmabuf, char *name)
+{
+ if (!name)
+ return -EINVAL;
+
+ /* dmabuffs_dname() won't use the string if the length
+ * (including terminator) exceeds DMA_BUF_NAME_LEN:
+ */
+ if (strlen(name) >= DMA_BUF_NAME_LEN)
+ return -E2BIG;
+
+ spin_lock(&dmabuf->name_lock);
+ kfree(dmabuf->name);
+ dmabuf->name = name;
+ spin_unlock(&dmabuf->name_lock);
+
+ return 0;
+}
+EXPORT_SYMBOL_NS_GPL(dma_buf_set_name, "DMA_BUF");
+
static int dma_buf_wrap_sg_table(struct sg_table **sg_table)
{
struct scatterlist *to_sg, *from_sg;
@@ -1004,6 +1023,11 @@ dma_buf_pin_on_map(struct dma_buf_attachment *attach)
* functions:
*
* - dma_buf_invalidate_mappings()
+ *
+ * 4. Exporters must not hold the dma-buf reservation lock when calling these
+ * functions:
+ *
+ * - dma_buf_set_name()
*/
/**
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index d15b2b31d3c9..0f88132c0654 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -342,12 +342,14 @@ struct dma_buf {
/**
* @name:
*
- * Userspace-provided name. Default value is NULL. If not NULL,
- * length cannot be longer than DMA_BUF_NAME_LEN, including NIL
- * char. Useful for accounting and debugging. Read/Write accesses
- * are protected by @name_lock
- *
- * See the IOCTLs DMA_BUF_SET_NAME or DMA_BUF_SET_NAME_A/B
+ * Exporter or userspace-provided name. Default value is
+ * NULL. If not NULL, length cannot be longer than
+ * DMA_BUF_NAME_LEN, including NIL char. Useful for accounting
+ * and debugging. Read/Write accesses are protected by
+ * @name_lock
+ *
+ * See dma_buf_set_name(), and the IOCTLs DMA_BUF_SET_NAME or
+ * DMA_BUF_SET_NAME_A/B
*/
const char *name;
@@ -571,6 +573,8 @@ void dma_buf_fd_install(struct dma_buf *dmabuf, int fd);
struct dma_buf *dma_buf_get(int fd);
void dma_buf_put(struct dma_buf *dmabuf);
+int dma_buf_set_name(struct dma_buf *dmabuf, char *name);
+
struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *,
enum dma_data_direction);
void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *,
--
2.47.3
^ permalink raw reply [flat|nested] 11+ messages in thread* Re: [PATCH v8 3/9] dma-buf: Provide dma_buf_set_name()
2026-10-06 19:36 ` [PATCH v8 3/9] dma-buf: Provide dma_buf_set_name() Matt Evans
@ 2026-10-07 9:22 ` Christian König
0 siblings, 0 replies; 11+ messages in thread
From: Christian König @ 2026-10-07 9:22 UTC (permalink / raw)
To: Matt Evans, Alex Williamson, Leon Romanovsky, Jason Gunthorpe,
Alex Mastro, Kevin Tian, Pranjal Shrivastava, Longfang Liu
Cc: Mahmoud Adam, David Matlack, Björn Töpel, Sumit Semwal,
Ankit Agrawal, Alistair Popple, Vivek Kasireddy, linux-kernel,
linux-media, dri-devel, linaro-mm-sig, kvm, linux-pci
On 10/6/26 21:36, Matt Evans wrote:
> Allow exporters to set the name of buffers, during export or for
> subsequent updates. This is useful to express buffer-specific debug
> information, indicate state particular to the exporter's usage, etc.
> Only exporters and userspace are expected to set names; it isn't
> sensible for importers to do it.
>
> Originally, the static dma_buf_set_name() was used for
> DMA_BUF_SET_NAME ioctls, taking a __user string parameter. Export
> this function as a generic set-name helper, taking a kernel-allocated
> string. The SET_NAME ioctls now locally duplicate the __user string,
> and use the new function to set the name.
>
> Signed-off-by: Matt Evans <matt@ozlabs.org>
Reviewed-by: Christian König <christian.koenig@amd.com>
> ---
> drivers/dma-buf/dma-buf.c | 84 +++++++++++++++++++++++++--------------
> include/linux/dma-buf.h | 16 +++++---
> 2 files changed, 64 insertions(+), 36 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 4c9add51f9ef..b99da4ff2ef6 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -404,34 +404,6 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
> return events;
> }
>
> -/**
> - * dma_buf_set_name - Set a name to a specific dma_buf to track the usage.
> - * It could support changing the name of the dma-buf if the same
> - * piece of memory is used for multiple purpose between different devices.
> - *
> - * @dmabuf: [in] dmabuf buffer that will be renamed.
> - * @buf: [in] A piece of userspace memory that contains the name of
> - * the dma-buf.
> - *
> - * Returns 0 on success. If the dma-buf buffer is already attached to
> - * devices, return -EBUSY.
> - *
> - */
> -static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf)
> -{
> - char *name = strndup_user(buf, DMA_BUF_NAME_LEN);
> -
> - if (IS_ERR(name))
> - return PTR_ERR(name);
> -
> - spin_lock(&dmabuf->name_lock);
> - kfree(dmabuf->name);
> - dmabuf->name = name;
> - spin_unlock(&dmabuf->name_lock);
> -
> - return 0;
> -}
> -
> #if IS_ENABLED(CONFIG_SYNC_FILE)
> static long dma_buf_export_sync_file(struct dma_buf *dmabuf,
> void __user *user_data)
> @@ -577,8 +549,19 @@ static long dma_buf_ioctl(struct file *file,
> return ret;
>
> case DMA_BUF_SET_NAME_A:
> - case DMA_BUF_SET_NAME_B:
> - return dma_buf_set_name(dmabuf, (const char __user *)arg);
> + case DMA_BUF_SET_NAME_B: {
> + char *name = strndup_user((const char __user *)arg,
> + DMA_BUF_NAME_LEN);
> +
> + if (IS_ERR(name))
> + return PTR_ERR(name);
> +
> + ret = dma_buf_set_name(dmabuf, name);
> + if (ret)
> + kfree(name);
> +
> + return ret;
> + }
>
> #if IS_ENABLED(CONFIG_SYNC_FILE)
> case DMA_BUF_IOCTL_EXPORT_SYNC_FILE:
> @@ -874,6 +857,42 @@ void dma_buf_put(struct dma_buf *dmabuf)
> }
> EXPORT_SYMBOL_NS_GPL(dma_buf_put, "DMA_BUF");
>
> +/**
> + * dma_buf_set_name - Set a dmabuf's name
> + * @dmabuf: [in] dmabuf buffer that will be renamed.
> + * @name: [in] The name of the dma-buf, allocated with kmalloc() or
> + * similar. This takes ownership of the allocation
> + * on success, which will be kfree()d when the
> + * dmabuf is released or a new name assigned.
> + *
> + * Intended to be used by the exporter to set a name for debug
> + * purposes. This can also change an existing name if the same piece
> + * of memory is used for multiple purposes over time. Importers
> + * should NOT use this function to overwrite the name.
> + *
> + * Return: 0 on success, -EINVAL if the name is NULL, or -E2BIG if the
> + * name (including terminator) exceeds DMA_BUF_NAME_LEN.
> + */
> +int dma_buf_set_name(struct dma_buf *dmabuf, char *name)
> +{
> + if (!name)
> + return -EINVAL;
> +
> + /* dmabuffs_dname() won't use the string if the length
> + * (including terminator) exceeds DMA_BUF_NAME_LEN:
> + */
> + if (strlen(name) >= DMA_BUF_NAME_LEN)
> + return -E2BIG;
> +
> + spin_lock(&dmabuf->name_lock);
> + kfree(dmabuf->name);
> + dmabuf->name = name;
> + spin_unlock(&dmabuf->name_lock);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_NS_GPL(dma_buf_set_name, "DMA_BUF");
> +
> static int dma_buf_wrap_sg_table(struct sg_table **sg_table)
> {
> struct scatterlist *to_sg, *from_sg;
> @@ -1004,6 +1023,11 @@ dma_buf_pin_on_map(struct dma_buf_attachment *attach)
> * functions:
> *
> * - dma_buf_invalidate_mappings()
> + *
> + * 4. Exporters must not hold the dma-buf reservation lock when calling these
> + * functions:
> + *
> + * - dma_buf_set_name()
> */
>
> /**
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index d15b2b31d3c9..0f88132c0654 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -342,12 +342,14 @@ struct dma_buf {
> /**
> * @name:
> *
> - * Userspace-provided name. Default value is NULL. If not NULL,
> - * length cannot be longer than DMA_BUF_NAME_LEN, including NIL
> - * char. Useful for accounting and debugging. Read/Write accesses
> - * are protected by @name_lock
> - *
> - * See the IOCTLs DMA_BUF_SET_NAME or DMA_BUF_SET_NAME_A/B
> + * Exporter or userspace-provided name. Default value is
> + * NULL. If not NULL, length cannot be longer than
> + * DMA_BUF_NAME_LEN, including NIL char. Useful for accounting
> + * and debugging. Read/Write accesses are protected by
> + * @name_lock
> + *
> + * See dma_buf_set_name(), and the IOCTLs DMA_BUF_SET_NAME or
> + * DMA_BUF_SET_NAME_A/B
> */
> const char *name;
>
> @@ -571,6 +573,8 @@ void dma_buf_fd_install(struct dma_buf *dmabuf, int fd);
> struct dma_buf *dma_buf_get(int fd);
> void dma_buf_put(struct dma_buf *dmabuf);
>
> +int dma_buf_set_name(struct dma_buf *dmabuf, char *name);
> +
> struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *,
> enum dma_data_direction);
> void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *,
^ permalink raw reply [flat|nested] 11+ messages in thread
* [PATCH v8 4/9] vfio/pci: Add a helper to look up PFNs for DMABUFs
2026-10-06 19:36 [PATCH v8 0/9] vfio/pci: Add mmap() for DMABUFs Matt Evans
` (2 preceding siblings ...)
2026-10-06 19:36 ` [PATCH v8 3/9] dma-buf: Provide dma_buf_set_name() Matt Evans
@ 2026-10-06 19:36 ` Matt Evans
2026-10-06 19:36 ` [PATCH v8 5/9] vfio/pci: Add a helper to create a DMABUF for a BAR-map VMA Matt Evans
` (4 subsequent siblings)
8 siblings, 0 replies; 11+ messages in thread
From: Matt Evans @ 2026-10-06 19:36 UTC (permalink / raw)
To: Alex Williamson, Leon Romanovsky, Jason Gunthorpe, Alex Mastro,
Christian König, Kevin Tian, Pranjal Shrivastava,
Longfang Liu
Cc: Mahmoud Adam, David Matlack, Björn Töpel, Sumit Semwal,
Ankit Agrawal, Alistair Popple, Vivek Kasireddy, linux-kernel,
linux-media, dri-devel, linaro-mm-sig, kvm, linux-pci
Add vfio_pci_dma_buf_find_pfn(), which a VMA fault handler can use to
find a PFN.
This supports multi-range DMABUFs, which typically would be used to
represent scattered spans but might even represent overlapping or
aliasing spans of PFNs.
Because this is intended to be used in vfio_pci_core.c, we also need
to expose the struct vfio_pci_dma_buf in the vfio_pci_priv.h header.
This move also adds a new member, vma_pgoff_adjust; this is consumed
by vfio_pci_dma_buf_find_pfn(), but will be set in a future commit.
Add it now to reduce the number of functions touched by later commits.
Signed-off-by: Matt Evans <matt@ozlabs.org>
---
drivers/vfio/pci/vfio_pci_dmabuf.c | 166 ++++++++++++++++++++++++++---
drivers/vfio/pci/vfio_pci_priv.h | 21 ++++
2 files changed, 174 insertions(+), 13 deletions(-)
diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
index 847ee5cc78e7..9f10b10fc436 100644
--- a/drivers/vfio/pci/vfio_pci_dmabuf.c
+++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
@@ -9,19 +9,6 @@
MODULE_IMPORT_NS("DMA_BUF");
-struct vfio_pci_dma_buf {
- struct dma_buf *dmabuf;
- struct vfio_pci_core_device *vdev;
- struct list_head dmabufs_elm;
- size_t size;
- struct phys_vec *phys_vec;
- struct p2pdma_provider *provider;
- u32 nr_ranges;
- struct kref kref;
- struct completion comp;
- u8 revoked : 1;
-};
-
static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
struct dma_buf_attachment *attachment)
{
@@ -106,6 +93,159 @@ static const struct dma_buf_ops vfio_pci_dmabuf_ops = {
.release = vfio_pci_dma_buf_release,
};
+int vfio_pci_dma_buf_find_pfn(struct vfio_pci_core_device *vdev,
+ struct vfio_pci_dma_buf *priv,
+ struct vm_area_struct *vma,
+ unsigned long fault_addr,
+ unsigned int order,
+ unsigned long *out_pfn)
+{
+ /*
+ * Given a VMA (start, end, pgoffs) and a fault address,
+ * search the corresponding DMABUF's phys_vec[] to find the
+ * range representing the address's offset into the VMA, and
+ * its PFN. vdev must be the device that the DMABUF priv was
+ * exported from; vdev->dmabuf_lock must be held, and priv
+ * must not be revoked.
+ *
+ * The phys_vec[] ranges represent contiguous spans of VAs
+ * upwards from the buffer offset 0; the actual PFNs might be
+ * in any order, overlap/alias, etc. Calculate an offset of
+ * the desired page given VMA start/pgoff and address, then
+ * search upwards from 0 to find which span contains it.
+ *
+ * On success, a valid PFN for a page sized by 'order' is
+ * returned into out_pfn.
+ *
+ * Failure occurs if:
+ * - A hugepage would cross the edge of the VMA,
+ * - A hugepage isn't entirely contained within a range
+ * (including where it straddles the boundary between
+ * ranges),
+ * - We find a range, but the final PFN isn't aligned to the
+ * requested order.
+ *
+ * Upon failure, -ERANGE is returned and the caller is
+ * expected to try again with a smaller order, which will
+ * eventually succeed.
+ *
+ * It's suboptimal if DMABUFs are created with neighbouring
+ * ranges that are physically contiguous, since hugepages
+ * can't straddle range boundaries. (The construction of the
+ * ranges should merge them in this case.)
+ *
+ * Finally, vma_pgoff_adjust is used with a DMABUF created for
+ * a VFIO BAR mmap: a BAR mapped with vm_pgoff > 0 creates a
+ * DMABUF such that byte 0 of the VMA corresponds to byte 0 of
+ * the DMABUF and byte 'vm_pgoff << PAGE_SHIFT' into the BAR.
+ * To avoid double-offsetting in this scenario, subtracting
+ * vma_pgoff_adjust from this (non-zero) vm_pgoff generates
+ * the effective offset. This also removes the VFIO region
+ * index encoded in vm_pgoff for VFIO BAR mmaps.
+ */
+
+ const unsigned long pagesize = PAGE_SIZE << order;
+ unsigned long vma_off = (vma->vm_pgoff - priv->vma_pgoff_adjust) <<
+ PAGE_SHIFT;
+ unsigned long rounded_page_addr = ALIGN_DOWN(fault_addr, pagesize);
+ unsigned long rounded_page_end = rounded_page_addr + pagesize;
+ unsigned long fault_offset;
+ unsigned long fault_offset_end;
+ unsigned long range_start_offset = 0;
+ unsigned int i;
+ int ret;
+
+ if (unlikely(!vdev))
+ return -ENODEV;
+
+ /* This prevents the dmabuf revocation state from changing under us */
+ lockdep_assert_held(&vdev->dmabuf_lock);
+
+ if (unlikely(priv->vdev != vdev || priv->revoked))
+ return -ENODEV;
+
+ if (rounded_page_addr < vma->vm_start || rounded_page_end > vma->vm_end) {
+ if (order > 0)
+ return -ERANGE;
+
+ /* A fault address outside of the VMA is absurd. */
+ dev_warn_ratelimited(
+ &vdev->pdev->dev,
+ "Fault addr 0x%lx outside VMA 0x%lx-0x%lx\n",
+ fault_addr, vma->vm_start, vma->vm_end);
+ return -EFAULT;
+ }
+
+ /*
+ * fault_offset[_end] is the span within the DMABUF
+ * corresponding to the faulting page:
+ */
+ if (unlikely(check_add_overflow(rounded_page_addr - vma->vm_start,
+ vma_off, &fault_offset) ||
+ check_add_overflow(fault_offset, pagesize,
+ &fault_offset_end)))
+ return -EFAULT;
+
+ /*
+ * Iterate over ranges in the buffer, summing their lengths:
+ * range_start_offset represents the current range's starting
+ * offset in the buffer (from 0 upwards).
+ *
+ * A failure for order == 0 is unexpected, and triggers a
+ * fault/warn.
+ */
+ ret = (order == 0) ? -EFAULT : -ERANGE;
+
+ for (i = 0; i < priv->nr_ranges; i++) {
+ size_t range_len = priv->phys_vec[i].len;
+
+ /* Early exit if range starts after the page end */
+ if (fault_offset_end <= range_start_offset)
+ break;
+
+ if (fault_offset >= range_start_offset &&
+ fault_offset_end <= range_start_offset + range_len) {
+ /*
+ * The faulting page is wholly contained
+ * within the span represented by this range,
+ * so validate PFN alignment for the order.
+ * The if() condition ensures the pfn
+ * arithmetic won't overflow.
+ */
+ unsigned long pfn =
+ ((fault_offset - range_start_offset) +
+ priv->phys_vec[i].paddr) >> PAGE_SHIFT;
+
+ if (IS_ALIGNED(pfn, 1 << order)) {
+ *out_pfn = pfn;
+ ret = 0;
+ }
+ /*
+ * Else order > 0; ERANGE retries with smaller
+ * order
+ */
+ break;
+ }
+ range_start_offset += range_len;
+ }
+
+ if (order == 0 && ret != 0)
+ /*
+ * The address fell outside of the span represented by
+ * the (concatenated) ranges. As setup of a mapping
+ * ensures that the VMA is <= the total size of the
+ * ranges this should never happen. If it does, warn
+ * and SIGBUS.
+ */
+ dev_warn_ratelimited(
+ &vdev->pdev->dev,
+ "No range for addr 0x%lx, order %d: VMA 0x%lx-0x%lx pgoff 0x%lx, %u ranges, size 0x%zx\n",
+ fault_addr, order, vma->vm_start, vma->vm_end,
+ vma->vm_pgoff, priv->nr_ranges, priv->size);
+
+ return ret;
+}
+
/*
* This is a temporary "private interconnect" between VFIO DMABUF and iommufd.
* It allows the two co-operating drivers to exchange the physical address of
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index 4e7162234a2e..786df3a81d9d 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -23,6 +23,20 @@ struct vfio_pci_ioeventfd {
bool test_mem;
};
+struct vfio_pci_dma_buf {
+ struct dma_buf *dmabuf;
+ struct vfio_pci_core_device *vdev;
+ struct list_head dmabufs_elm;
+ size_t size;
+ struct phys_vec *phys_vec;
+ struct p2pdma_provider *provider;
+ u32 nr_ranges;
+ struct kref kref;
+ struct completion comp;
+ unsigned long vma_pgoff_adjust;
+ u8 revoked : 1;
+};
+
bool vfio_pci_intx_mask(struct vfio_pci_core_device *vdev);
void vfio_pci_intx_unmask(struct vfio_pci_core_device *vdev);
@@ -123,6 +137,13 @@ static inline bool vfio_pci_is_vga(struct pci_dev *pdev)
return (pdev->class >> 8) == PCI_CLASS_DISPLAY_VGA;
}
+int vfio_pci_dma_buf_find_pfn(struct vfio_pci_core_device *vdev,
+ struct vfio_pci_dma_buf *priv,
+ struct vm_area_struct *vma,
+ unsigned long address,
+ unsigned int order,
+ unsigned long *out_pfn);
+
#ifdef CONFIG_VFIO_PCI_DMABUF
int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
struct vfio_device_feature_dma_buf __user *arg,
--
2.47.3
^ permalink raw reply [flat|nested] 11+ messages in thread* [PATCH v8 5/9] vfio/pci: Add a helper to create a DMABUF for a BAR-map VMA
2026-10-06 19:36 [PATCH v8 0/9] vfio/pci: Add mmap() for DMABUFs Matt Evans
` (3 preceding siblings ...)
2026-10-06 19:36 ` [PATCH v8 4/9] vfio/pci: Add a helper to look up PFNs for DMABUFs Matt Evans
@ 2026-10-06 19:36 ` Matt Evans
2026-10-06 19:36 ` [PATCH v8 6/9] vfio/pci: Convert BAR mmap() to use a DMABUF Matt Evans
` (3 subsequent siblings)
8 siblings, 0 replies; 11+ messages in thread
From: Matt Evans @ 2026-10-06 19:36 UTC (permalink / raw)
To: Alex Williamson, Leon Romanovsky, Jason Gunthorpe, Alex Mastro,
Christian König, Kevin Tian, Pranjal Shrivastava,
Longfang Liu
Cc: Mahmoud Adam, David Matlack, Björn Töpel, Sumit Semwal,
Ankit Agrawal, Alistair Popple, Vivek Kasireddy, linux-kernel,
linux-media, dri-devel, linaro-mm-sig, kvm, linux-pci
This helper, vfio_pci_core_mmap_prep_dmabuf(), creates a single-range
DMABUF for the purpose of mapping a PCI BAR. This is used in a future
commit by VFIO's ordinary mmap() path.
This function transfers ownership of the VFIO device fd to the
DMABUF, which fput()s when it's released.
Refactor the existing vfio_pci_core_feature_dma_buf() to split out
export code common to the two paths, VFIO_DEVICE_FEATURE_DMA_BUF and
this new VFIO_BAR mmap().
By exchanging the VMA file, we lose the original device path in
/proc/<pid>/maps, lsof, etc. Generate a debug-oriented synthetic
'filename' for BAR mappings based on the BDF, plus resource index.
(This does not apply to explicitly-exported DMABUFs which are named by
DMA_BUF_SET_NAME.)
Signed-off-by: Matt Evans <matt@ozlabs.org>
---
drivers/vfio/pci/vfio_pci_dmabuf.c | 209 ++++++++++++++++++++++-------
drivers/vfio/pci/vfio_pci_priv.h | 5 +
2 files changed, 169 insertions(+), 45 deletions(-)
diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
index 9f10b10fc436..fd3ee2f5c5e8 100644
--- a/drivers/vfio/pci/vfio_pci_dmabuf.c
+++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
@@ -3,6 +3,7 @@
*/
#include <linux/dma-buf-mapping.h>
#include <linux/pci-p2pdma.h>
+#include <linux/dma-buf.h>
#include <linux/dma-resv.h>
#include "vfio_pci_priv.h"
@@ -82,6 +83,8 @@ static void vfio_pci_dma_buf_release(struct dma_buf *dmabuf)
up_write(&priv->vdev->dmabuf_lock);
vfio_device_put_registration(&priv->vdev->vdev);
}
+ if (priv->vfile)
+ fput(priv->vfile);
kfree(priv->phys_vec);
kfree(priv);
}
@@ -246,6 +249,165 @@ int vfio_pci_dma_buf_find_pfn(struct vfio_pci_core_device *vdev,
return ret;
}
+/*
+ * Create a DMABUF corresponding to priv, add it to vdev->dmabufs list
+ * for tracking (meaning cleanup or revocation will zap it), and take
+ * a vfio_device registration.
+ */
+static int vfio_pci_dmabuf_export(struct vfio_pci_core_device *vdev,
+ struct vfio_pci_dma_buf *priv, u32 flags)
+{
+ DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
+
+ if (!vfio_device_try_get_registration(&vdev->vdev))
+ return -ENODEV;
+
+ exp_info.ops = &vfio_pci_dmabuf_ops;
+ exp_info.size = priv->size;
+ exp_info.flags = flags;
+ exp_info.priv = priv;
+
+ priv->dmabuf = dma_buf_export(&exp_info);
+ if (IS_ERR(priv->dmabuf)) {
+ vfio_device_put_registration(&vdev->vdev);
+ return PTR_ERR(priv->dmabuf);
+ }
+
+ kref_init(&priv->kref);
+ init_completion(&priv->comp);
+
+ /* dma_buf_put() now frees priv */
+ INIT_LIST_HEAD(&priv->dmabufs_elm);
+
+ /*
+ * dmabuf_lock synchronises access (R) or updates (W) to the
+ * vdev->dmabufs list and to bars_revoked (see below). The
+ * revocation state of DMABUF elements in the list is written
+ * holding both dmabuf_lock(W) and resv, and tested with
+ * either.
+ *
+ * (memory_lock, if held ->) dmabuf_lock -> resv
+ *
+ * NOTE: memory_lock is strictly avoided here, to avoid a
+ * dependency on memory_lock when mmap_lock is held, when
+ * mmap() leads to export. vfio-pci variant drivers are
+ * permitted to hold memory_lock across actions that might
+ * fault (such as user access); a deadlock could result when
+ * that fault path attempts to take mmap_lock (if held by an
+ * export waiting for memory_lock).
+ *
+ * vdev->bars_revoked tracks the BAR revocation status updated
+ * via vfio_pci_dma_buf_move(), so the initial DMABUF state
+ * follows the same criteria that later update the DMABUF
+ * state (BAR zap, etc.).
+ */
+ lockdep_assert_not_held(&vdev->memory_lock);
+
+ down_write(&vdev->dmabuf_lock);
+ dma_resv_lock(priv->dmabuf->resv, NULL);
+ priv->revoked = vdev->bars_revoked;
+ list_add_tail(&priv->dmabufs_elm, &vdev->dmabufs);
+ dma_resv_unlock(priv->dmabuf->resv);
+ up_write(&vdev->dmabuf_lock);
+
+ return 0;
+}
+
+int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
+ struct vm_area_struct *vma,
+ u64 phys_start, u64 req_len,
+ unsigned int res_index)
+{
+ struct vfio_pci_dma_buf *priv;
+ unsigned long vma_pgoff = vma->vm_pgoff & (VFIO_PCI_OFFSET_MASK >> PAGE_SHIFT);
+ char *bufname;
+ int ret;
+
+ priv = kzalloc_obj(*priv);
+ if (!priv)
+ return -ENOMEM;
+
+ priv->phys_vec = kzalloc_obj(*priv->phys_vec);
+ if (!priv->phys_vec) {
+ ret = -ENOMEM;
+ goto err_free_priv;
+ }
+
+ /*
+ * Debug name: The absolute maximum size of the name
+ * ('vfio:ffffffff:ff:1f.7/5') fits within DMA_BUF_NAME_LEN.
+ */
+ bufname = kasprintf(GFP_KERNEL, "vfio:%s/%x",
+ pci_name(vdev->pdev),
+ res_index);
+
+ if (!bufname) {
+ ret = -ENOMEM;
+ goto err_free_phys;
+ }
+
+ /*
+ * The DMABUF begins from the mmap()'s BAR offset, i.e. the
+ * start of the VMA corresponds to byte 0 of the DMABUF and
+ * byte (vma_pgoff << PAGE_SHIFT) of the BAR.
+ *
+ * vfio_pci_dma_buf_find_pfn() reverses this offset using
+ * vma_pgoff_adjust, so that ultimately a fault's offset from
+ * the start of the _VMA_ has a consistent usage whether the
+ * VMA originates from an mmap() of the VFIO device here or a
+ * direct DMABUF mmap(). Note vma_pgoff_adjust also includes
+ * the encoded VFIO region index, which cancels out the index
+ * encoded in vm_pgoff.
+ */
+ priv->vdev = vdev;
+ priv->size = req_len;
+ priv->nr_ranges = 1;
+ priv->vma_pgoff_adjust = vma->vm_pgoff;
+
+ priv->provider = pcim_p2pdma_provider(vdev->pdev, res_index);
+ if (!priv->provider) {
+ ret = -EINVAL;
+ goto err_free_name;
+ }
+
+ priv->phys_vec[0].paddr = phys_start + ((u64)vma_pgoff << PAGE_SHIFT);
+ priv->phys_vec[0].len = priv->size;
+
+ ret = vfio_pci_dmabuf_export(vdev, priv, O_RDWR);
+ if (ret)
+ goto err_free_name;
+
+ if (dma_buf_set_name(priv->dmabuf, bufname)) {
+ dev_dbg_ratelimited(&vdev->pdev->dev,
+ "Failed to set map name '%s'\n",
+ bufname);
+ kfree(bufname);
+ }
+
+ /*
+ * Ownership of the DMABUF file transfers to the VMA so that
+ * other users can locate the DMABUF via a VA. Ownership of
+ * the original VFIO device file being mmap()ed transfers to
+ * priv, and is put when the DMABUF is released. This
+ * intentionally does not use get_file()/vma_set_file()
+ * because the references are already held, and ownership
+ * moves.
+ */
+ priv->vfile = vma->vm_file;
+ vma->vm_file = priv->dmabuf->file;
+ vma->vm_private_data = priv;
+
+ return 0;
+
+err_free_name:
+ kfree(bufname);
+err_free_phys:
+ kfree(priv->phys_vec);
+err_free_priv:
+ kfree(priv);
+ return ret;
+}
+
/*
* This is a temporary "private interconnect" between VFIO DMABUF and iommufd.
* It allows the two co-operating drivers to exchange the physical address of
@@ -364,7 +526,6 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
{
struct vfio_device_feature_dma_buf get_dma_buf = {};
struct vfio_region_dma_range *dma_ranges;
- DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
struct vfio_pci_dma_buf *priv;
size_t length;
int ret;
@@ -424,49 +585,9 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
kfree(dma_ranges);
dma_ranges = NULL;
- if (!vfio_device_try_get_registration(&vdev->vdev)) {
- ret = -ENODEV;
+ ret = vfio_pci_dmabuf_export(vdev, priv, get_dma_buf.open_flags);
+ if (ret)
goto err_free_phys;
- }
-
- exp_info.ops = &vfio_pci_dmabuf_ops;
- exp_info.size = priv->size;
- exp_info.flags = get_dma_buf.open_flags;
- exp_info.priv = priv;
-
- priv->dmabuf = dma_buf_export(&exp_info);
- if (IS_ERR(priv->dmabuf)) {
- ret = PTR_ERR(priv->dmabuf);
- goto err_dev_put;
- }
-
- kref_init(&priv->kref);
- init_completion(&priv->comp);
-
- /* dma_buf_put() now frees priv */
- INIT_LIST_HEAD(&priv->dmabufs_elm);
-
- /*
- * dmabuf_lock synchronises access (R) or updates (W) to the
- * vdev->dmabufs list and to bars_revoked (see below). The
- * revocation state of DMABUF elements in the list is written
- * holding both dmabuf_lock(W) and resv, and tested with
- * either.
- *
- * dmabuf_lock -> resv
- *
- * vdev->bars_revoked tracks the BAR revocation status updated
- * via vfio_pci_dma_buf_move(), so the initial DMABUF state
- * follows the same criteria that later update the DMABUF
- * state (BAR zap, etc.).
- */
- down_write(&vdev->dmabuf_lock);
- dma_resv_lock(priv->dmabuf->resv, NULL);
- priv->revoked = vdev->bars_revoked;
- list_add_tail(&priv->dmabufs_elm, &vdev->dmabufs);
- dma_resv_unlock(priv->dmabuf->resv);
- up_write(&vdev->dmabuf_lock);
-
/*
* dma_buf_fd() consumes the reference, when the file closes the dmabuf
* will be released.
@@ -477,8 +598,6 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
return ret;
-err_dev_put:
- vfio_device_put_registration(&vdev->vdev);
err_free_phys:
kfree(priv->phys_vec);
err_free_priv:
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index 786df3a81d9d..66a5ae19082d 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -30,6 +30,7 @@ struct vfio_pci_dma_buf {
size_t size;
struct phys_vec *phys_vec;
struct p2pdma_provider *provider;
+ struct file *vfile;
u32 nr_ranges;
struct kref kref;
struct completion comp;
@@ -143,6 +144,10 @@ int vfio_pci_dma_buf_find_pfn(struct vfio_pci_core_device *vdev,
unsigned long address,
unsigned int order,
unsigned long *out_pfn);
+int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
+ struct vm_area_struct *vma,
+ u64 phys_start, u64 req_len,
+ unsigned int res_index);
#ifdef CONFIG_VFIO_PCI_DMABUF
int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
--
2.47.3
^ permalink raw reply [flat|nested] 11+ messages in thread* [PATCH v8 6/9] vfio/pci: Convert BAR mmap() to use a DMABUF
2026-10-06 19:36 [PATCH v8 0/9] vfio/pci: Add mmap() for DMABUFs Matt Evans
` (4 preceding siblings ...)
2026-10-06 19:36 ` [PATCH v8 5/9] vfio/pci: Add a helper to create a DMABUF for a BAR-map VMA Matt Evans
@ 2026-10-06 19:36 ` Matt Evans
2026-10-06 19:36 ` [PATCH v8 7/9] vfio/pci: Clean up BAR zap and revocation Matt Evans
` (2 subsequent siblings)
8 siblings, 0 replies; 11+ messages in thread
From: Matt Evans @ 2026-10-06 19:36 UTC (permalink / raw)
To: Alex Williamson, Leon Romanovsky, Jason Gunthorpe, Alex Mastro,
Christian König, Kevin Tian, Pranjal Shrivastava,
Longfang Liu
Cc: Mahmoud Adam, David Matlack, Björn Töpel, Sumit Semwal,
Ankit Agrawal, Alistair Popple, Vivek Kasireddy, linux-kernel,
linux-media, dri-devel, linaro-mm-sig, kvm, linux-pci
Convert the VFIO device fd fops->mmap to create a DMABUF representing
the BAR mapping, and make the VMA fault handler look up PFNs from the
corresponding DMABUF. This supports future code mmap()ing BAR
DMABUFs, and iommufd work to support Type1 P2P.
First, vfio_pci_core_mmap() uses the new
vfio_pci_core_mmap_prep_dmabuf() helper to export a DMABUF
representing a single BAR range. Then, the vfio_pci_mmap_huge_fault()
callback is updated to understand revoked buffers, and uses the new
vfio_pci_dma_buf_find_pfn() helper to determine the PFN for a given
fault address.
Now that the VFIO DMABUFs can be mmap()ed, vfio_pci_dma_buf_move()
zaps PTEs (used on the revocation and cleanup paths).
CONFIG_VFIO_PCI_CORE now unconditionally selects
CONFIG_DMA_SHARED_BUFFER. The CONFIG_VFIO_PCI_DMABUF feature
conditionally includes support for VFIO_DEVICE_FEATURE_DMA_BUF,
depending on the availability of CONFIG_PCI_P2PDMA.
When the DMABUF feature is not present, DMABUFs are used internally
for the BAR mappings. In this case, DMABUF attach is prohibited (and
the requirement for a P2PDMA provider is relaxed).
Signed-off-by: Matt Evans <matt@ozlabs.org>
Tested-by: Alex Mastro <amastro@fb.com>
Reviewed-by: Alex Mastro <amastro@fb.com>
---
drivers/vfio/pci/Kconfig | 4 +-
drivers/vfio/pci/Makefile | 3 +-
drivers/vfio/pci/vfio_pci_core.c | 71 ++++++++++++++++++------------
drivers/vfio/pci/vfio_pci_dmabuf.c | 24 +++++++++-
drivers/vfio/pci/vfio_pci_priv.h | 11 +----
5 files changed, 73 insertions(+), 40 deletions(-)
diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig
index 296bf01e185e..c6d6fb09af86 100644
--- a/drivers/vfio/pci/Kconfig
+++ b/drivers/vfio/pci/Kconfig
@@ -6,6 +6,7 @@ config VFIO_PCI_CORE
tristate
select VFIO_VIRQFD
select IRQ_BYPASS_MANAGER
+ select DMA_SHARED_BUFFER
config VFIO_PCI_INTX
def_bool y if !S390
@@ -56,7 +57,8 @@ config VFIO_PCI_ZDEV_KVM
To enable s390x KVM vfio-pci extensions, say Y.
config VFIO_PCI_DMABUF
- def_bool y if VFIO_PCI_CORE && PCI_P2PDMA && DMA_SHARED_BUFFER
+ def_bool y if PCI_P2PDMA
+ depends on VFIO_PCI_CORE
source "drivers/vfio/pci/mlx5/Kconfig"
diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
index 6138f1bf241d..881452ea89be 100644
--- a/drivers/vfio/pci/Makefile
+++ b/drivers/vfio/pci/Makefile
@@ -1,8 +1,7 @@
# SPDX-License-Identifier: GPL-2.0-only
-vfio-pci-core-y := vfio_pci_core.o vfio_pci_intrs.o vfio_pci_rdwr.o vfio_pci_config.o
+vfio-pci-core-y := vfio_pci_core.o vfio_pci_intrs.o vfio_pci_rdwr.o vfio_pci_config.o vfio_pci_dmabuf.o
vfio-pci-core-$(CONFIG_VFIO_PCI_ZDEV_KVM) += vfio_pci_zdev.o
-vfio-pci-core-$(CONFIG_VFIO_PCI_DMABUF) += vfio_pci_dmabuf.o
obj-$(CONFIG_VFIO_PCI_CORE) += vfio-pci-core.o
vfio-pci-y := vfio_pci.o
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index e170cdc7ac92..cb0e4865d110 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -1748,18 +1748,6 @@ void vfio_pci_memory_unlock_and_restore(struct vfio_pci_core_device *vdev, u16 c
up_write(&vdev->memory_lock);
}
-static unsigned long vma_to_pfn(struct vm_area_struct *vma)
-{
- struct vfio_pci_core_device *vdev = vma->vm_private_data;
- int index = vma->vm_pgoff >> (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT);
- u64 pgoff;
-
- pgoff = vma->vm_pgoff &
- ((1U << (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT)) - 1);
-
- return (pci_resource_start(vdev->pdev, index) >> PAGE_SHIFT) + pgoff;
-}
-
vm_fault_t vfio_pci_vmf_insert_pfn(struct vfio_pci_core_device *vdev,
struct vm_fault *vmf,
unsigned long pfn,
@@ -1787,23 +1775,46 @@ static vm_fault_t vfio_pci_mmap_huge_fault(struct vm_fault *vmf,
unsigned int order)
{
struct vm_area_struct *vma = vmf->vma;
- struct vfio_pci_core_device *vdev = vma->vm_private_data;
- unsigned long addr = vmf->address & ~((PAGE_SIZE << order) - 1);
- unsigned long pgoff = linear_page_delta(vma, addr);
- unsigned long pfn = vma_to_pfn(vma) + pgoff;
- vm_fault_t ret = VM_FAULT_FALLBACK;
-
- if (is_aligned_for_order(vma, addr, pfn, order)) {
- scoped_guard(rwsem_read, &vdev->memory_lock)
- ret = vfio_pci_vmf_insert_pfn(vdev, vmf, pfn, order);
+ struct vfio_pci_dma_buf *priv = vma->vm_private_data;
+ struct vfio_pci_core_device *vdev;
+ unsigned long pfn = 0;
+ vm_fault_t ret = VM_FAULT_SIGBUS;
+
+ /*
+ * We can rely on the existence of both a DMABUF (priv) and
+ * the VFIO device it was exported from (vdev). This fault's
+ * VMA was established using vfio_pci_core_mmap_prep_dmabuf()
+ * which transfers ownership of the VFIO device fd to the
+ * DMABUF, and so the VFIO device is held open because the
+ * VMA's vm_file (DMABUF) is open.
+ *
+ * Since vfio_pci_dma_buf_cleanup() cannot have happened,
+ * vdev must be valid; we can take vdev locks.
+ */
+ vdev = priv->vdev;
+
+ /* memory_lock for vfio_pci_vmf_insert_pfn() */
+ down_read(&vdev->memory_lock);
+ /* Test revocation status under dmabuf_lock */
+ down_read(&vdev->dmabuf_lock);
+ if (!priv->revoked) {
+ int pres = vfio_pci_dma_buf_find_pfn(vdev, priv, vma,
+ vmf->address,
+ order, &pfn);
+
+ if (pres == 0)
+ ret = vfio_pci_vmf_insert_pfn(vdev, vmf,
+ pfn, order);
+ else if (pres == -ERANGE)
+ ret = VM_FAULT_FALLBACK;
}
+ up_read(&vdev->dmabuf_lock);
+ up_read(&vdev->memory_lock);
dev_dbg_ratelimited(&vdev->pdev->dev,
- "%s(,order = %d) BAR %ld page offset 0x%lx: 0x%x\n",
- __func__, order,
- vma->vm_pgoff >>
- (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT),
- pgoff, (unsigned int)ret);
+ "%s(order = %d) PFN 0x%lx, VA 0x%lx, pgoff 0x%lx: 0x%x\n",
+ __func__, order, pfn, vmf->address,
+ vma->vm_pgoff, (unsigned int)ret);
return ret;
}
@@ -1828,6 +1839,7 @@ int vfio_pci_core_mmap(struct vfio_device *core_vdev, struct vm_area_struct *vma
unsigned int index;
u64 phys_len, req_len, pgoff, req_start;
void __iomem *bar_io;
+ int ret;
index = vma->vm_pgoff >> (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT);
@@ -1867,7 +1879,12 @@ int vfio_pci_core_mmap(struct vfio_device *core_vdev, struct vm_area_struct *vma
if (IS_ERR(bar_io))
return PTR_ERR(bar_io);
- vma->vm_private_data = vdev;
+ ret = vfio_pci_core_mmap_prep_dmabuf(vdev, vma,
+ pci_resource_start(pdev, index),
+ req_len, index);
+ if (ret)
+ return ret;
+
vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
index fd3ee2f5c5e8..617afb7de00f 100644
--- a/drivers/vfio/pci/vfio_pci_dmabuf.c
+++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
@@ -10,6 +10,7 @@
MODULE_IMPORT_NS("DMA_BUF");
+#ifdef CONFIG_VFIO_PCI_DMABUF
static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
struct dma_buf_attachment *attachment)
{
@@ -26,6 +27,18 @@ static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
return 0;
}
+#else
+static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
+ struct dma_buf_attachment *attachment)
+{
+ /*
+ * Explicit export can't occur without the DMABUF feature, but
+ * DMABUFs are implicitly created for BAR mappings. An
+ * .attach that fails prevents dma_buf_attach().
+ */
+ return -EOPNOTSUPP;
+}
+#endif /* CONFIG_VFIO_PCI_DMABUF */
static void vfio_pci_dma_buf_done(struct kref *kref)
{
@@ -364,8 +377,13 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
priv->nr_ranges = 1;
priv->vma_pgoff_adjust = vma->vm_pgoff;
+ /*
+ * The provider can be NULL _iff_ the DMABUF feature isn't
+ * supported, because it's only used by DMABUF import and
+ * attach is prohibited if the feature isn't present.
+ */
priv->provider = pcim_p2pdma_provider(vdev->pdev, res_index);
- if (!priv->provider) {
+ if (IS_ENABLED(CONFIG_VFIO_PCI_DMABUF) && !priv->provider) {
ret = -EINVAL;
goto err_free_name;
}
@@ -408,6 +426,7 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
return ret;
}
+#ifdef CONFIG_VFIO_PCI_DMABUF
/*
* This is a temporary "private interconnect" between VFIO DMABUF and iommufd.
* It allows the two co-operating drivers to exchange the physical address of
@@ -606,6 +625,7 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
kfree(dma_ranges);
return ret;
}
+#endif /* CONFIG_VFIO_PCI_DMABUF */
void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked)
{
@@ -632,6 +652,8 @@ void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked)
if (revoked) {
kref_put(&priv->kref, vfio_pci_dma_buf_done);
wait_for_completion(&priv->comp);
+ unmap_mapping_range(priv->dmabuf->file->f_mapping,
+ 0, 0, true);
/*
* Re-arm the registered kref reference and the
* completion so the post-revoke state matches the
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index 66a5ae19082d..ef6aabb9f5a4 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -148,13 +148,13 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
struct vm_area_struct *vma,
u64 phys_start, u64 req_len,
unsigned int res_index);
+void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev);
+void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked);
#ifdef CONFIG_VFIO_PCI_DMABUF
int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
struct vfio_device_feature_dma_buf __user *arg,
size_t argsz);
-void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev);
-void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked);
#else
static inline int
vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
@@ -163,13 +163,6 @@ vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
{
return -ENOTTY;
}
-static inline void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev)
-{
-}
-static inline void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev,
- bool revoked)
-{
-}
#endif
#endif
--
2.47.3
^ permalink raw reply [flat|nested] 11+ messages in thread* [PATCH v8 7/9] vfio/pci: Clean up BAR zap and revocation
2026-10-06 19:36 [PATCH v8 0/9] vfio/pci: Add mmap() for DMABUFs Matt Evans
` (5 preceding siblings ...)
2026-10-06 19:36 ` [PATCH v8 6/9] vfio/pci: Convert BAR mmap() to use a DMABUF Matt Evans
@ 2026-10-06 19:36 ` Matt Evans
2026-10-06 19:36 ` [PATCH v8 8/9] vfio/pci: Support mmap() of a VFIO DMABUF Matt Evans
2026-10-06 19:36 ` [PATCH v8 9/9] vfio/pci: Revoke a DMABUF on request from userspace Matt Evans
8 siblings, 0 replies; 11+ messages in thread
From: Matt Evans @ 2026-10-06 19:36 UTC (permalink / raw)
To: Alex Williamson, Leon Romanovsky, Jason Gunthorpe, Alex Mastro,
Christian König, Kevin Tian, Pranjal Shrivastava,
Longfang Liu
Cc: Mahmoud Adam, David Matlack, Björn Töpel, Sumit Semwal,
Ankit Agrawal, Alistair Popple, Vivek Kasireddy, linux-kernel,
linux-media, dri-devel, linaro-mm-sig, kvm, linux-pci
Previously, vfio_pci_zap_bars() (and the wrapper
vfio_pci_zap_and_down_write_memory_lock()) calls were paired with
calls to vfio_pci_dma_buf_move().
This commit replaces them with a unified new function,
vfio_pci_revoke_bars() containing both the vfio_pci_dma_buf_move() and
the unmap_mapping_range(), making it harder for callers to omit one.
It adds a wrapper, vfio_pci_lock_revoke_bars(), which takes the write
memory_lock before zapping, and adds a new vfio_pci_unrevoke_bars()
for the re-enable path.
As of "vfio/pci: Convert BAR mmap() to use a DMABUF", the zap via
unmap_mapping_range() is no longer performed for vfio-pci since the
DMABUFs used for BAR mappings already zap PTEs when the
vfio_pci_dma_buf_move() occurs.
However, it must be assumed that VFIO drivers which override the .mmap
op could create mappings _not_ backed by DMABUFs. So, the zap is
still performed on revoke if .mmap is overridden, using a new
zap_bars_on_revoke flag. A driver can explicitly opt out; the flag is
cleared by the hisi_acc_vfio_pci driver, since its .mmap just wraps
vfio_pci_core_mmap() and so still uses DMABUFs.
Signed-off-by: Matt Evans <matt@ozlabs.org>
---
.../vfio/pci/hisilicon/hisi_acc_vfio_pci.c | 14 +++-
drivers/vfio/pci/vfio_pci_config.c | 30 +++-----
drivers/vfio/pci/vfio_pci_core.c | 75 +++++++++++++------
drivers/vfio/pci/vfio_pci_priv.h | 3 +-
include/linux/vfio_pci_core.h | 1 +
5 files changed, 82 insertions(+), 41 deletions(-)
diff --git a/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c b/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
index 86362ec424a5..14622556355e 100644
--- a/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
+++ b/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
@@ -1564,6 +1564,7 @@ static int hisi_acc_vfio_pci_migrn_init_dev(struct vfio_device *core_vdev)
struct hisi_acc_vf_core_device *hisi_acc_vdev = hisi_acc_get_vf_dev(core_vdev);
struct pci_dev *pdev = to_pci_dev(core_vdev->dev);
struct hisi_qm *pf_qm = hisi_acc_get_pf_qm(pdev);
+ int ret;
hisi_acc_vdev->vf_id = pci_iov_vf_id(pdev) + 1;
hisi_acc_vdev->pf_qm = pf_qm;
@@ -1575,7 +1576,18 @@ static int hisi_acc_vfio_pci_migrn_init_dev(struct vfio_device *core_vdev)
core_vdev->migration_flags = VFIO_MIGRATION_STOP_COPY | VFIO_MIGRATION_PRE_COPY;
core_vdev->mig_ops = &hisi_acc_vfio_pci_migrn_state_ops;
- return vfio_pci_core_init_dev(core_vdev);
+ ret = vfio_pci_core_init_dev(core_vdev);
+ if (ret)
+ return ret;
+ /*
+ * hisi_acc_vfio_pci_mmap() calls down to
+ * vfio_pci_core_mmap(), so BAR mappings are still
+ * DMABUF-backed. They don't require a zap on revoke, so opt
+ * out:
+ */
+ hisi_acc_vdev->core_device.zap_bars_on_revoke = false;
+
+ return 0;
}
static const struct vfio_device_ops hisi_acc_vfio_pci_migrn_ops = {
diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
index 9914f3ac69ae..cef337f4e8f2 100644
--- a/drivers/vfio/pci/vfio_pci_config.c
+++ b/drivers/vfio/pci/vfio_pci_config.c
@@ -590,12 +590,10 @@ static int vfio_basic_config_write(struct vfio_pci_core_device *vdev, int pos,
virt_mem = !!(le16_to_cpu(*virt_cmd) & PCI_COMMAND_MEMORY);
new_mem = !!(new_cmd & PCI_COMMAND_MEMORY);
- if (!new_mem) {
- vfio_pci_zap_and_down_write_memory_lock(vdev);
- vfio_pci_dma_buf_move(vdev, true);
- } else {
+ if (!new_mem)
+ vfio_pci_lock_revoke_bars(vdev);
+ else
down_write(&vdev->memory_lock);
- }
/*
* If the user is writing mem/io enable (new_mem/io) and we
@@ -631,7 +629,7 @@ static int vfio_basic_config_write(struct vfio_pci_core_device *vdev, int pos,
*virt_cmd |= cpu_to_le16(new_cmd & mask);
if (__vfio_pci_memory_enabled(vdev))
- vfio_pci_dma_buf_move(vdev, false);
+ vfio_pci_unrevoke_bars(vdev);
up_write(&vdev->memory_lock);
}
@@ -712,16 +710,14 @@ static int __init init_pci_cap_basic_perm(struct perm_bits *perm)
static void vfio_lock_and_set_power_state(struct vfio_pci_core_device *vdev,
pci_power_t state)
{
- if (state >= PCI_D3hot) {
- vfio_pci_zap_and_down_write_memory_lock(vdev);
- vfio_pci_dma_buf_move(vdev, true);
- } else {
+ if (state >= PCI_D3hot)
+ vfio_pci_lock_revoke_bars(vdev);
+ else
down_write(&vdev->memory_lock);
- }
vfio_pci_set_power_state(vdev, state);
if (__vfio_pci_memory_enabled(vdev))
- vfio_pci_dma_buf_move(vdev, false);
+ vfio_pci_unrevoke_bars(vdev);
up_write(&vdev->memory_lock);
}
@@ -908,11 +904,10 @@ static int vfio_exp_config_write(struct vfio_pci_core_device *vdev, int pos,
&cap);
if (!ret && (cap & PCI_EXP_DEVCAP_FLR)) {
- vfio_pci_zap_and_down_write_memory_lock(vdev);
- vfio_pci_dma_buf_move(vdev, true);
+ vfio_pci_lock_revoke_bars(vdev);
pci_try_reset_function(vdev->pdev);
if (__vfio_pci_memory_enabled(vdev))
- vfio_pci_dma_buf_move(vdev, false);
+ vfio_pci_unrevoke_bars(vdev);
up_write(&vdev->memory_lock);
}
}
@@ -993,11 +988,10 @@ static int vfio_af_config_write(struct vfio_pci_core_device *vdev, int pos,
&cap);
if (!ret && (cap & PCI_AF_CAP_FLR) && (cap & PCI_AF_CAP_TP)) {
- vfio_pci_zap_and_down_write_memory_lock(vdev);
- vfio_pci_dma_buf_move(vdev, true);
+ vfio_pci_lock_revoke_bars(vdev);
pci_try_reset_function(vdev->pdev);
if (__vfio_pci_memory_enabled(vdev))
- vfio_pci_dma_buf_move(vdev, false);
+ vfio_pci_unrevoke_bars(vdev);
up_write(&vdev->memory_lock);
}
}
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index cb0e4865d110..986852b1d44f 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -376,8 +376,7 @@ static int vfio_pci_runtime_pm_entry(struct vfio_pci_core_device *vdev,
* The vdev power related flags are protected with 'memory_lock'
* semaphore.
*/
- vfio_pci_zap_and_down_write_memory_lock(vdev);
- vfio_pci_dma_buf_move(vdev, true);
+ vfio_pci_lock_revoke_bars(vdev);
if (vdev->pm_runtime_engaged) {
up_write(&vdev->memory_lock);
@@ -463,7 +462,7 @@ static void vfio_pci_runtime_pm_exit(struct vfio_pci_core_device *vdev)
down_write(&vdev->memory_lock);
__vfio_pci_runtime_pm_exit(vdev);
if (__vfio_pci_memory_enabled(vdev))
- vfio_pci_dma_buf_move(vdev, false);
+ vfio_pci_unrevoke_bars(vdev);
up_write(&vdev->memory_lock);
}
@@ -532,7 +531,7 @@ static int vfio_pci_core_runtime_resume(struct device *dev)
vdev->pm_wake_eventfd_ctx = NULL;
__vfio_pci_runtime_pm_exit(vdev);
if (__vfio_pci_memory_enabled(vdev))
- vfio_pci_dma_buf_move(vdev, false);
+ vfio_pci_unrevoke_bars(vdev);
eventfd_signal(ctx);
eventfd_ctx_put(ctx);
}
@@ -1319,6 +1318,8 @@ static int vfio_pci_ioctl_set_irqs(struct vfio_pci_core_device *vdev,
return ret;
}
+static void vfio_pci_revoke_bars(struct vfio_pci_core_device *vdev);
+
static int vfio_pci_ioctl_reset(struct vfio_pci_core_device *vdev,
void __user *arg)
{
@@ -1327,7 +1328,7 @@ static int vfio_pci_ioctl_reset(struct vfio_pci_core_device *vdev,
if (!vdev->reset_works)
return -EINVAL;
- vfio_pci_zap_and_down_write_memory_lock(vdev);
+ down_write(&vdev->memory_lock);
/*
* This function can be invoked while the power state is non-D0. If
@@ -1337,13 +1338,18 @@ static int vfio_pci_ioctl_reset(struct vfio_pci_core_device *vdev,
* have NoSoftRst-, the reset function can cause the PCI config space
* reset without restoring the original state (saved locally in
* 'vdev->pm_save').
+ *
+ * The zap is done after making the device accessible in D0,
+ * because a DMABUF importer could access the device as part
+ * of its revocation cleanup.
*/
vfio_pci_set_power_state(vdev, PCI_D0);
- vfio_pci_dma_buf_move(vdev, true);
+ vfio_pci_revoke_bars(vdev);
+
ret = pci_try_reset_function(vdev->pdev);
if (__vfio_pci_memory_enabled(vdev))
- vfio_pci_dma_buf_move(vdev, false);
+ vfio_pci_unrevoke_bars(vdev);
up_write(&vdev->memory_lock);
return ret;
@@ -1713,20 +1719,37 @@ ssize_t vfio_pci_core_write(struct vfio_device *core_vdev, const char __user *bu
}
EXPORT_SYMBOL_GPL(vfio_pci_core_write);
-static void vfio_pci_zap_bars(struct vfio_pci_core_device *vdev)
+static void vfio_pci_revoke_bars(struct vfio_pci_core_device *vdev)
{
- struct vfio_device *core_vdev = &vdev->vdev;
- loff_t start = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_BAR0_REGION_INDEX);
- loff_t end = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_ROM_REGION_INDEX);
- loff_t len = end - start;
+ lockdep_assert_held_write(&vdev->memory_lock);
+ vfio_pci_dma_buf_move(vdev, true);
- unmap_mapping_range(core_vdev->inode->i_mapping, start, len, true);
+ /*
+ * If a driver could possibly create BAR mappings in the
+ * vdev's address_space, do an additional zap on revoke. See
+ * vfio_pci_core_init_dev().
+ */
+ if (vdev->zap_bars_on_revoke) {
+ struct vfio_device *core_vdev = &vdev->vdev;
+ loff_t start = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_BAR0_REGION_INDEX);
+ loff_t end = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_ROM_REGION_INDEX);
+ loff_t len = end - start;
+
+ unmap_mapping_range(core_vdev->inode->i_mapping,
+ start, len, true);
+ }
}
-void vfio_pci_zap_and_down_write_memory_lock(struct vfio_pci_core_device *vdev)
+void vfio_pci_lock_revoke_bars(struct vfio_pci_core_device *vdev)
{
down_write(&vdev->memory_lock);
- vfio_pci_zap_bars(vdev);
+ vfio_pci_revoke_bars(vdev);
+}
+
+void vfio_pci_unrevoke_bars(struct vfio_pci_core_device *vdev)
+{
+ lockdep_assert_held_write(&vdev->memory_lock);
+ vfio_pci_dma_buf_move(vdev, false);
}
u16 vfio_pci_memory_lock_and_enable(struct vfio_pci_core_device *vdev)
@@ -2224,6 +2247,16 @@ int vfio_pci_core_init_dev(struct vfio_device *core_vdev)
init_rwsem(&vdev->dmabuf_lock);
xa_init(&vdev->ctx);
+ /*
+ * If a driver overrides .mmap, it has to be assumed that it
+ * might not use the DMABUF-backed core mmap; this flag
+ * enables a zap at revoke time. A driver can opt out by
+ * clearing this flag at init, if their .mmap override calls
+ * down to vfio_pci_core_mmap().
+ */
+ if (vdev->vdev.ops->mmap != vfio_pci_core_mmap)
+ vdev->zap_bars_on_revoke = true;
+
return 0;
}
EXPORT_SYMBOL_GPL(vfio_pci_core_init_dev);
@@ -2591,9 +2624,10 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
}
/*
- * Take the memory write lock for each device and zap BAR
- * mappings to prevent the user accessing the device while in
- * reset. Locking multiple devices is prone to deadlock,
+ * Take the memory write lock for each device and
+ * zap/revoke BAR mappings to prevent the user (or
+ * peers) accessing the device while in reset.
+ * Locking multiple devices is prone to deadlock,
* runaway and unwind if we hit contention.
*/
if (!down_write_trylock(&vdev->memory_lock)) {
@@ -2601,8 +2635,7 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
break;
}
- vfio_pci_dma_buf_move(vdev, true);
- vfio_pci_zap_bars(vdev);
+ vfio_pci_revoke_bars(vdev);
}
if (!list_entry_is_head(vdev,
@@ -2632,7 +2665,7 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
list_for_each_entry_from_reverse(vdev, &dev_set->device_list,
vdev.dev_set_list) {
if (vdev->vdev.open_count && __vfio_pci_memory_enabled(vdev))
- vfio_pci_dma_buf_move(vdev, false);
+ vfio_pci_unrevoke_bars(vdev);
up_write(&vdev->memory_lock);
}
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index ef6aabb9f5a4..f11b31f8953c 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -83,7 +83,8 @@ void vfio_config_free(struct vfio_pci_core_device *vdev);
int vfio_pci_set_power_state(struct vfio_pci_core_device *vdev,
pci_power_t state);
-void vfio_pci_zap_and_down_write_memory_lock(struct vfio_pci_core_device *vdev);
+void vfio_pci_lock_revoke_bars(struct vfio_pci_core_device *vdev);
+void vfio_pci_unrevoke_bars(struct vfio_pci_core_device *vdev);
u16 vfio_pci_memory_lock_and_enable(struct vfio_pci_core_device *vdev);
void vfio_pci_memory_unlock_and_restore(struct vfio_pci_core_device *vdev,
u16 cmd);
diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
index f99b152edcca..44891fdb7c76 100644
--- a/include/linux/vfio_pci_core.h
+++ b/include/linux/vfio_pci_core.h
@@ -129,6 +129,7 @@ struct vfio_pci_core_device {
bool disable_idle_d3:1;
bool nointxmask:1;
bool disable_vga:1;
+ bool zap_bars_on_revoke:1;
/* Flags modified at runtime - dedicated storage unit */
bool needs_reset;
bool pm_intx_masked;
--
2.47.3
^ permalink raw reply [flat|nested] 11+ messages in thread* [PATCH v8 8/9] vfio/pci: Support mmap() of a VFIO DMABUF
2026-10-06 19:36 [PATCH v8 0/9] vfio/pci: Add mmap() for DMABUFs Matt Evans
` (6 preceding siblings ...)
2026-10-06 19:36 ` [PATCH v8 7/9] vfio/pci: Clean up BAR zap and revocation Matt Evans
@ 2026-10-06 19:36 ` Matt Evans
2026-10-06 19:36 ` [PATCH v8 9/9] vfio/pci: Revoke a DMABUF on request from userspace Matt Evans
8 siblings, 0 replies; 11+ messages in thread
From: Matt Evans @ 2026-10-06 19:36 UTC (permalink / raw)
To: Alex Williamson, Leon Romanovsky, Jason Gunthorpe, Alex Mastro,
Christian König, Kevin Tian, Pranjal Shrivastava,
Longfang Liu
Cc: Mahmoud Adam, David Matlack, Björn Töpel, Sumit Semwal,
Ankit Agrawal, Alistair Popple, Vivek Kasireddy, linux-kernel,
linux-media, dri-devel, linaro-mm-sig, kvm, linux-pci
A VFIO DMABUF can export a subset of a BAR to userspace by fd; add
support for mmap() of this fd. This provides another route for a
process to map BARs, in which the process can only map a specific
subset of a BAR represented by the exported DMABUF.
mmap() support enables userspace drivers to safely delegate BAR
sub-ranges to other processes by sharing a DMABUF fd, without having
to share the (omnipotent) VFIO device fd with them.
Since the main VFIO BAR mmap() is now DMABUF-aware, the new mmap() reuses
the existing vm_ops.
The lifecycle of an exported DMABUF remains decoupled from that of the
device fd it came from, i.e. the device fd could be closed with DMABUF
VMAs present, meaning a fault on a VMA could happen concurrently with
vfio_pci_dma_buf_cleanup().
To deal with this scenario, the fault handler now temporarily takes a
VFIO device registration to ensure the vdev remains valid, and then
vdev locks can be taken.
Signed-off-by: Matt Evans <matt@ozlabs.org>
---
drivers/vfio/pci/vfio_pci_core.c | 84 ++++++++++++++++++++++++++----
drivers/vfio/pci/vfio_pci_dmabuf.c | 47 +++++++++++++++++
drivers/vfio/pci/vfio_pci_priv.h | 1 +
3 files changed, 123 insertions(+), 9 deletions(-)
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 986852b1d44f..4926c7c95544 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -13,6 +13,8 @@
#include <linux/aperture.h>
#include <linux/debugfs.h>
#include <linux/device.h>
+#include <linux/dma-buf.h>
+#include <linux/dma-resv.h>
#include <linux/eventfd.h>
#include <linux/file.h>
#include <linux/interrupt.h>
@@ -1804,21 +1806,79 @@ static vm_fault_t vfio_pci_mmap_huge_fault(struct vm_fault *vmf,
vm_fault_t ret = VM_FAULT_SIGBUS;
/*
- * We can rely on the existence of both a DMABUF (priv) and
- * the VFIO device it was exported from (vdev). This fault's
- * VMA was established using vfio_pci_core_mmap_prep_dmabuf()
- * which transfers ownership of the VFIO device fd to the
- * DMABUF, and so the VFIO device is held open because the
- * VMA's vm_file (DMABUF) is open.
+ * The only thing this can rely on is that the DMABUF relating
+ * to the VMA's vm_file exists (priv).
*
- * Since vfio_pci_dma_buf_cleanup() cannot have happened,
- * vdev must be valid; we can take vdev locks.
+ * A DMABUF for a VFIO device fd mmap() holds a reference to
+ * the original VFIO device fd, but an explicitly-exported
+ * DMABUF does not. The original fd might have closed,
+ * meaning this fault can race with
+ * vfio_pci_dma_buf_cleanup(), meaning the buffer could have
+ * been revoked (in which case priv->vdev might be NULL), and
+ * the VFIO device registration might have been dropped.
+ *
+ * With the goal of taking vdev locks in a world where vdev
+ * might not still exist:
+ *
+ * 1. Take the resv lock on the DMABUF:
+ * - If racing cleanup got in first, the buffer is revoked;
+ * stop/exit if so.
+ * - If we got in first, the buffer is not revoked so vdev is
+ * non-NULL, accessible, and cleanup _has not yet put the
+ * VFIO device registration_. So, the device refcount must
+ * be >0.
+ *
+ * 2. Take vfio_device registration (refcount guaranteed >0
+ * hereafter).
+ *
+ * 3. Unlock the DMABUF's resv lock:
+ * - A racing cleanup can now complete.
+ * - But, the device refcount >0, meaning the vfio_device
+ * (and vfio_pci_core_device vdev) have not yet been
+ * freed. vdev is accessible, even if the DMABUF has been
+ * revoked or cleanup has happened, because
+ * vfio_unregister_group_dev() can't complete.
+ *
+ * 4. Take the vdev->memory_lock then vdev->dmabuf_lock:
+ * - Either the DMABUF is usable, or has been cleaned up.
+ * - It's not necessary to also take the resv lock, because
+ * the status/vdev can't change while dmabuf_lock is held.
+ * - Test the DMABUF revocation status again: if it was
+ * revoked between 1 and 4, return a SIGBUS. Otherwise,
+ * return a PFN.
+ *
+ * 5. Unlock, done.
*/
+
+ dma_resv_lock(priv->dmabuf->resv, NULL);
+
+ if (priv->revoked) {
+ pr_debug_ratelimited("%s VA 0x%lx, pgoff 0x%lx: DMABUF revoked/cleaned up\n",
+ __func__, vmf->address, vma->vm_pgoff);
+ dma_resv_unlock(priv->dmabuf->resv);
+ return VM_FAULT_SIGBUS;
+ }
+
+ /* If the buffer isn't revoked, vdev is valid */
vdev = priv->vdev;
+ if (!vfio_device_try_get_registration(&vdev->vdev)) {
+ /*
+ * If vdev != NULL (above), the registration should
+ * already be >0 and so this try_get should never
+ * fail.
+ */
+ dev_warn_ratelimited(&vdev->pdev->dev,
+ "%s: Unexpected registration failure\n",
+ __func__);
+ dma_resv_unlock(priv->dmabuf->resv);
+ return VM_FAULT_SIGBUS;
+ }
+ dma_resv_unlock(priv->dmabuf->resv);
+
/* memory_lock for vfio_pci_vmf_insert_pfn() */
down_read(&vdev->memory_lock);
- /* Test revocation status under dmabuf_lock */
+ /* Re-test revocation status under dmabuf_lock */
down_read(&vdev->dmabuf_lock);
if (!priv->revoked) {
int pres = vfio_pci_dma_buf_find_pfn(vdev, priv, vma,
@@ -1839,6 +1899,7 @@ static vm_fault_t vfio_pci_mmap_huge_fault(struct vm_fault *vmf,
__func__, order, pfn, vmf->address,
vma->vm_pgoff, (unsigned int)ret);
+ vfio_device_put_registration(&vdev->vdev);
return ret;
}
@@ -1854,6 +1915,11 @@ static const struct vm_operations_struct vfio_pci_mmap_ops = {
#endif
};
+void vfio_pci_set_vma_ops(struct vm_area_struct *vma)
+{
+ vma->vm_ops = &vfio_pci_mmap_ops;
+}
+
int vfio_pci_core_mmap(struct vfio_device *core_vdev, struct vm_area_struct *vma)
{
struct vfio_pci_core_device *vdev =
diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
index 617afb7de00f..c0a48d17c829 100644
--- a/drivers/vfio/pci/vfio_pci_dmabuf.c
+++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
@@ -27,6 +27,50 @@ static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
return 0;
}
+
+static int vfio_pci_dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
+{
+ struct vfio_pci_dma_buf *priv = dmabuf->priv;
+
+ /*
+ * dma_buf_mmap_internal() has asserted that the VMA is
+ * contained within the DMABUF size before calling this.
+ *
+ * Also, if we observe that the buffer is revoked now then
+ * refuse the mmap(). This is a belt-and-braces early failure
+ * to ease debugging a revoked buffer being used. Userspace
+ * might also race an mmap() against an explicit revocation,
+ * or an action causing a revoke; race scenarios are still
+ * safe because the fault handler ultimately prevents access
+ * to a revoked buffer if it isn't caught here.
+ */
+ if (priv->revoked)
+ return -ENODEV;
+ /*
+ * Make clear that anything with an offset adjustment is
+ * explicitly unsupported, as vfio_pci_dma_buf_find_pfn()
+ * maths would underflow; this doesn't happen through the
+ * regular DMABUF export path used with this mmap(). A DMABUF
+ * implicitly created for BAR mmap could have adjust > 0, but
+ * these can't currently be re-opened and mmap()ed again.
+ * Catch here in case that assumption ever changes.
+ */
+ if (priv->vma_pgoff_adjust)
+ return -EINVAL;
+ if ((vma->vm_flags & VM_SHARED) == 0)
+ return -EINVAL;
+
+ vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+ vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
+
+ /* See comments in vfio_pci_core_mmap() re VM_ALLOW_ANY_UNCACHED. */
+ vm_flags_set(vma, VM_ALLOW_ANY_UNCACHED | VM_IO | VM_PFNMAP |
+ VM_DONTEXPAND | VM_DONTDUMP);
+ vma->vm_private_data = priv;
+ vfio_pci_set_vma_ops(vma);
+
+ return 0;
+}
#else
static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
struct dma_buf_attachment *attachment)
@@ -104,6 +148,9 @@ static void vfio_pci_dma_buf_release(struct dma_buf *dmabuf)
static const struct dma_buf_ops vfio_pci_dmabuf_ops = {
.attach = vfio_pci_dma_buf_attach,
+#ifdef CONFIG_VFIO_PCI_DMABUF
+ .mmap = vfio_pci_dma_buf_mmap,
+#endif
.map_dma_buf = vfio_pci_dma_buf_map,
.unmap_dma_buf = vfio_pci_dma_buf_unmap,
.release = vfio_pci_dma_buf_release,
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index f11b31f8953c..32d520cac52f 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -151,6 +151,7 @@ int vfio_pci_core_mmap_prep_dmabuf(struct vfio_pci_core_device *vdev,
unsigned int res_index);
void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev);
void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked);
+void vfio_pci_set_vma_ops(struct vm_area_struct *vma);
#ifdef CONFIG_VFIO_PCI_DMABUF
int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
--
2.47.3
^ permalink raw reply [flat|nested] 11+ messages in thread* [PATCH v8 9/9] vfio/pci: Revoke a DMABUF on request from userspace
2026-10-06 19:36 [PATCH v8 0/9] vfio/pci: Add mmap() for DMABUFs Matt Evans
` (7 preceding siblings ...)
2026-10-06 19:36 ` [PATCH v8 8/9] vfio/pci: Support mmap() of a VFIO DMABUF Matt Evans
@ 2026-10-06 19:36 ` Matt Evans
8 siblings, 0 replies; 11+ messages in thread
From: Matt Evans @ 2026-10-06 19:36 UTC (permalink / raw)
To: Alex Williamson, Leon Romanovsky, Jason Gunthorpe, Alex Mastro,
Christian König, Kevin Tian, Pranjal Shrivastava,
Longfang Liu
Cc: Mahmoud Adam, David Matlack, Björn Töpel, Sumit Semwal,
Ankit Agrawal, Alistair Popple, Vivek Kasireddy, linux-kernel,
linux-media, dri-devel, linaro-mm-sig, kvm, linux-pci
Replace the VFIO exporter's priv->revoked flag with a status enum of
OK, REVOKED, and DEAD. OK and REVOKED are equivalent to the existing
flag, which tracks whether invalidate_mappings & unmap has occurred
and whether attach/map are permitted.
The DMABUF is marked DEAD in response to a new VFIO feature
VFIO_DEVICE_FEATURE_DMA_BUF_REVOKE. This passes a DMABUF by fd and
requests that the DMABUF is immediately revoked. On success, it's
guaranteed that PTEs are zapped, imports have been cleanly unmapped,
and that the buffer can never be mapped/attached or mmap()ed anymore.
Existing VFIO move semantics could permit a buffer to be mapped again
in future (e.g. revoke/unrevoke around a reset), but the DEAD state
can never become OK again.
This enables a userspace driver process to securely reclaim VFIO PCI
BAR resources previously delegated to a subordinate process. Using
the new ioctl, the userspace driver process can ensure that resources
are inaccessible when the subordinate is deemed "done". The
originally-exported DMABUF becomes unusable, and BAR resources can
then be safely re-exported for use elsewhere.
Refactor the revocation code out of vfio_pci_dma_buf_move() to a
function common to move and the new feature request path. This
function calls dma_buf_invalidate_mappings() and
dma_resv_wait_timeout() only on the revoke path
(vfio_pci_dma_buf_move() originally called them for both revoke and,
unnecessarily, for un-revoke).
Signed-off-by: Matt Evans <matt@ozlabs.org>
---
drivers/vfio/pci/vfio_pci_core.c | 6 +-
drivers/vfio/pci/vfio_pci_dmabuf.c | 181 ++++++++++++++++++++++-------
drivers/vfio/pci/vfio_pci_priv.h | 19 ++-
include/uapi/linux/vfio.h | 24 ++++
4 files changed, 188 insertions(+), 42 deletions(-)
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 4926c7c95544..68e582ad3846 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -1642,6 +1642,8 @@ int vfio_pci_core_ioctl_feature(struct vfio_device *device, u32 flags,
return vfio_pci_core_feature_dma_buf(vdev, flags, arg, argsz);
case VFIO_DEVICE_FEATURE_ZPCI_ERROR:
return vfio_pci_zdev_feature_err(device, flags, arg, argsz);
+ case VFIO_DEVICE_FEATURE_DMA_BUF_REVOKE:
+ return vfio_pci_core_feature_dma_buf_revoke(vdev, flags, arg, argsz);
default:
return -ENOTTY;
}
@@ -1852,7 +1854,7 @@ static vm_fault_t vfio_pci_mmap_huge_fault(struct vm_fault *vmf,
dma_resv_lock(priv->dmabuf->resv, NULL);
- if (priv->revoked) {
+ if (priv->status != VFIO_PCI_DMABUF_OK) {
pr_debug_ratelimited("%s VA 0x%lx, pgoff 0x%lx: DMABUF revoked/cleaned up\n",
__func__, vmf->address, vma->vm_pgoff);
dma_resv_unlock(priv->dmabuf->resv);
@@ -1880,7 +1882,7 @@ static vm_fault_t vfio_pci_mmap_huge_fault(struct vm_fault *vmf,
down_read(&vdev->memory_lock);
/* Re-test revocation status under dmabuf_lock */
down_read(&vdev->dmabuf_lock);
- if (!priv->revoked) {
+ if (priv->status == VFIO_PCI_DMABUF_OK) {
int pres = vfio_pci_dma_buf_find_pfn(vdev, priv, vma,
vmf->address,
order, &pfn);
diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
index c0a48d17c829..b57bfaefd9fa 100644
--- a/drivers/vfio/pci/vfio_pci_dmabuf.c
+++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
@@ -19,7 +19,7 @@ static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
if (!attachment->peer2peer)
return -EOPNOTSUPP;
- if (priv->revoked)
+ if (READ_ONCE(priv->status) != VFIO_PCI_DMABUF_OK)
return -ENODEV;
if (!dma_buf_attach_revocable(attachment))
@@ -44,7 +44,7 @@ static int vfio_pci_dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *
* safe because the fault handler ultimately prevents access
* to a revoked buffer if it isn't caught here.
*/
- if (priv->revoked)
+ if (READ_ONCE(priv->status) != VFIO_PCI_DMABUF_OK)
return -ENODEV;
/*
* Make clear that anything with an offset adjustment is
@@ -101,7 +101,7 @@ vfio_pci_dma_buf_map(struct dma_buf_attachment *attachment,
dma_resv_assert_held(priv->dmabuf->resv);
- if (priv->revoked)
+ if (priv->status != VFIO_PCI_DMABUF_OK)
return ERR_PTR(-ENODEV);
ret = dma_buf_phys_vec_to_sgt(attachment, priv->provider,
@@ -224,7 +224,7 @@ int vfio_pci_dma_buf_find_pfn(struct vfio_pci_core_device *vdev,
/* This prevents the dmabuf revocation state from changing under us */
lockdep_assert_held(&vdev->dmabuf_lock);
- if (unlikely(priv->vdev != vdev || priv->revoked))
+ if (unlikely(priv->vdev != vdev || priv->status != VFIO_PCI_DMABUF_OK))
return -ENODEV;
if (rounded_page_addr < vma->vm_start || rounded_page_end > vma->vm_end) {
@@ -365,7 +365,8 @@ static int vfio_pci_dmabuf_export(struct vfio_pci_core_device *vdev,
down_write(&vdev->dmabuf_lock);
dma_resv_lock(priv->dmabuf->resv, NULL);
- priv->revoked = vdev->bars_revoked;
+ priv->status = vdev->bars_revoked ? VFIO_PCI_DMABUF_REVOKED :
+ VFIO_PCI_DMABUF_OK;
list_add_tail(&priv->dmabufs_elm, &vdev->dmabufs);
dma_resv_unlock(priv->dmabuf->resv);
up_write(&vdev->dmabuf_lock);
@@ -496,7 +497,7 @@ int vfio_pci_dma_buf_iommufd_map(struct dma_buf_attachment *attachment,
return -EOPNOTSUPP;
priv = attachment->dmabuf->priv;
- if (priv->revoked)
+ if (priv->status != VFIO_PCI_DMABUF_OK)
return -ENODEV;
/* More than one range to iommufd will require proper DMABUF support */
@@ -674,6 +675,68 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
}
#endif /* CONFIG_VFIO_PCI_DMABUF */
+/*
+ * Set the DMABUF's revocation status (OK, REVOKED, DEAD): DEAD gives
+ * the guarantee that all future map/attach attempts will fail no
+ * matter what, whereas REVOKED can transition back to OK.
+ */
+static void vfio_pci_dma_buf_set_status(struct vfio_pci_dma_buf *priv,
+ enum vfio_pci_dma_buf_status new_status)
+{
+ bool was_revoked;
+
+ /*
+ * Changes to the DMABUF's revocation status are synchronised
+ * using dmabuf_lock:
+ */
+ lockdep_assert_held_write(&priv->vdev->dmabuf_lock);
+
+ /* If DEAD, state can no longer change */
+ if (priv->status == VFIO_PCI_DMABUF_DEAD ||
+ priv->status == new_status)
+ return;
+
+ dma_resv_lock(priv->dmabuf->resv, NULL);
+ was_revoked = (priv->status == VFIO_PCI_DMABUF_REVOKED);
+
+ if (new_status != VFIO_PCI_DMABUF_OK) {
+ priv->status = new_status;
+
+ if (was_revoked) {
+ /*
+ * A REVOKED buffer is being marked DEAD.
+ * invalidate_mappings/unmap wait happened
+ * when it became REVOKED, don't wait again.
+ */
+ dma_resv_unlock(priv->dmabuf->resv);
+ return;
+ }
+ dma_buf_invalidate_mappings(priv->dmabuf);
+ dma_resv_wait_timeout(priv->dmabuf->resv,
+ DMA_RESV_USAGE_BOOKKEEP, false,
+ MAX_SCHEDULE_TIMEOUT);
+ dma_resv_unlock(priv->dmabuf->resv);
+ kref_put(&priv->kref, vfio_pci_dma_buf_done);
+ wait_for_completion(&priv->comp);
+ unmap_mapping_range(priv->dmabuf->file->f_mapping,
+ 0, 0, true);
+ /*
+ * Re-arm the registered kref reference and the
+ * completion so the post-revoke state matches the
+ * post-creation state. An un-revoke followed by a
+ * new mapping needs the kref to be non-zero before
+ * kref_get(), and vfio_pci_dma_buf_cleanup()
+ * delegates its drain back through this revoke
+ * path on a possibly-already-revoked dma-buf.
+ */
+ kref_init(&priv->kref);
+ reinit_completion(&priv->comp);
+ } else {
+ priv->status = VFIO_PCI_DMABUF_OK;
+ dma_resv_unlock(priv->dmabuf->resv);
+ }
+}
+
void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked)
{
struct vfio_pci_dma_buf *priv;
@@ -686,38 +749,9 @@ void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked)
list_for_each_entry_safe(priv, tmp, &vdev->dmabufs, dmabufs_elm) {
if (!get_file_active(&priv->dmabuf->file))
continue;
-
- if (priv->revoked != revoked) {
- dma_resv_lock(priv->dmabuf->resv, NULL);
- if (revoked)
- priv->revoked = true;
- dma_buf_invalidate_mappings(priv->dmabuf);
- dma_resv_wait_timeout(priv->dmabuf->resv,
- DMA_RESV_USAGE_BOOKKEEP, false,
- MAX_SCHEDULE_TIMEOUT);
- dma_resv_unlock(priv->dmabuf->resv);
- if (revoked) {
- kref_put(&priv->kref, vfio_pci_dma_buf_done);
- wait_for_completion(&priv->comp);
- unmap_mapping_range(priv->dmabuf->file->f_mapping,
- 0, 0, true);
- /*
- * Re-arm the registered kref reference and the
- * completion so the post-revoke state matches the
- * post-creation state. An un-revoke followed by a
- * new mapping needs the kref to be non-zero before
- * kref_get(), and vfio_pci_dma_buf_cleanup()
- * delegates its drain back through this revoke
- * path on a possibly-already-revoked dma-buf.
- */
- kref_init(&priv->kref);
- reinit_completion(&priv->comp);
- } else {
- dma_resv_lock(priv->dmabuf->resv, NULL);
- priv->revoked = false;
- dma_resv_unlock(priv->dmabuf->resv);
- }
- }
+ vfio_pci_dma_buf_set_status(priv, revoked ?
+ VFIO_PCI_DMABUF_REVOKED :
+ VFIO_PCI_DMABUF_OK);
fput(priv->dmabuf->file);
}
up_write(&vdev->dmabuf_lock);
@@ -745,10 +779,79 @@ void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev)
continue;
list_del_init(&priv->dmabufs_elm);
- priv->vdev = NULL;
+ WRITE_ONCE(priv->vdev, NULL);
vfio_device_put_registration(&vdev->vdev);
fput(priv->dmabuf->file);
}
up_write(&vdev->dmabuf_lock);
up_write(&vdev->memory_lock);
}
+
+#ifdef CONFIG_VFIO_PCI_DMABUF
+int vfio_pci_core_feature_dma_buf_revoke(
+ struct vfio_pci_core_device *vdev, u32 flags,
+ struct vfio_device_feature_dma_buf_revoke __user *arg,
+ size_t argsz)
+{
+ struct vfio_device_feature_dma_buf_revoke db_revoke;
+ struct vfio_pci_dma_buf *priv;
+ struct dma_buf *dmabuf;
+ int ret;
+
+ if (!vdev->pci_ops || !vdev->pci_ops->get_dmabuf_phys)
+ return -EOPNOTSUPP;
+
+ ret = vfio_check_feature(flags, argsz,
+ VFIO_DEVICE_FEATURE_SET,
+ sizeof(db_revoke));
+ if (ret != 1)
+ return ret;
+
+ if (copy_from_user(&db_revoke, arg, sizeof(db_revoke)))
+ return -EFAULT;
+
+ dmabuf = dma_buf_get(db_revoke.dmabuf_fd);
+ if (IS_ERR(dmabuf))
+ return PTR_ERR(dmabuf);
+
+ priv = dmabuf->priv;
+ /*
+ * Sanity-check the DMABUF is really a vfio_pci_dma_buf _and_
+ * relates to the VFIO device it was provided with.
+ *
+ * If the DMABUF relates to this vdev then priv->vdev is
+ * stable because this open fd prevents cleanup.
+ *
+ * If it relates to a different vdev, reading priv->vdev might
+ * race with a concurrent cleanup on that device. But if so,
+ * it points to a non-matching vdev or NULL and is unusable
+ * either way.
+ */
+ if (dmabuf->ops != &vfio_pci_dmabuf_ops ||
+ READ_ONCE(priv->vdev) != vdev) {
+ ret = -ENODEV;
+ goto out_put_buf;
+ }
+
+ /*
+ * memory_lock(R) is taken to stop vfio_pci_dev_set_hot_reset()
+ * from getting it and then blocking all devices in the dev_set behind
+ * this revoke's drain.
+ */
+ down_read(&vdev->memory_lock);
+ down_write(&vdev->dmabuf_lock);
+ if (priv->status == VFIO_PCI_DMABUF_DEAD) {
+ ret = -EBADFD;
+ } else {
+ vfio_pci_dma_buf_set_status(priv, VFIO_PCI_DMABUF_DEAD);
+ ret = 0;
+ }
+ up_write(&vdev->dmabuf_lock);
+ up_read(&vdev->memory_lock);
+
+out_put_buf:
+ dma_buf_put(dmabuf);
+
+ return ret;
+}
+#endif /* CONFIG_VFIO_PCI_DMABUF */
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index 32d520cac52f..ca12221af555 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -23,6 +23,12 @@ struct vfio_pci_ioeventfd {
bool test_mem;
};
+enum vfio_pci_dma_buf_status {
+ VFIO_PCI_DMABUF_OK = 0,
+ VFIO_PCI_DMABUF_REVOKED = 1,
+ VFIO_PCI_DMABUF_DEAD = 2,
+};
+
struct vfio_pci_dma_buf {
struct dma_buf *dmabuf;
struct vfio_pci_core_device *vdev;
@@ -35,7 +41,7 @@ struct vfio_pci_dma_buf {
struct kref kref;
struct completion comp;
unsigned long vma_pgoff_adjust;
- u8 revoked : 1;
+ enum vfio_pci_dma_buf_status status;
};
bool vfio_pci_intx_mask(struct vfio_pci_core_device *vdev);
@@ -157,6 +163,10 @@ void vfio_pci_set_vma_ops(struct vm_area_struct *vma);
int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
struct vfio_device_feature_dma_buf __user *arg,
size_t argsz);
+int vfio_pci_core_feature_dma_buf_revoke(
+ struct vfio_pci_core_device *vdev, u32 flags,
+ struct vfio_device_feature_dma_buf_revoke __user *arg,
+ size_t argsz);
#else
static inline int
vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
@@ -165,6 +175,13 @@ vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
{
return -ENOTTY;
}
+static inline int vfio_pci_core_feature_dma_buf_revoke(
+ struct vfio_pci_core_device *vdev, u32 flags,
+ struct vfio_device_feature_dma_buf_revoke __user *arg,
+ size_t argsz)
+{
+ return -ENOTTY;
+}
#endif
#endif
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index e41437fa17ad..d3c6057983e0 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -1555,6 +1555,30 @@ struct vfio_device_feature_zpci_err {
#define VFIO_DEVICE_FEATURE_ZPCI_ERROR 13
+/**
+ * Given a DMABUF fd previously exported from the same device by
+ * VFIO_DEVICE_FEATURE_DMA_BUF, a SET of this feature requests that
+ * access to the corresponding DMABUF is immediately revoked. On
+ * successful return, the buffer is no longer accessible through any
+ * VMA or DMABUF import. Thereafter, VFIO also refuses all future
+ * mmap()s and map/attach requests from any new/existing importer.
+ *
+ * Return: 0 on success, -1 and errno is set on failure:
+ *
+ * EBADF, EINVAL: dmabuf_fd is not a DMABUF fd.
+ * EOPNOTSUPP: The VFIO device does not support DMABUF export.
+ * ENODEV: The DMABUF was not exported from this device.
+ * EBADFD: The DMABUF is already revoked by this feature.
+ *
+ * Additionally, common errors can occur: EFAULT accessing the struct,
+ * or EINVAL requesting an unsupported feature op.
+ */
+#define VFIO_DEVICE_FEATURE_DMA_BUF_REVOKE 14
+
+struct vfio_device_feature_dma_buf_revoke {
+ __s32 dmabuf_fd;
+};
+
/* -------- API for Type1 VFIO IOMMU -------- */
/**
--
2.47.3
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