[PATCH v2 0/3] drm/virtio: introduce F_BLOB_ALIGNMENT support

[PATCH v2 0/3] drm/virtio: introduce F_BLOB_ALIGNMENT support

[Sergio Lopez]

There's an increasing number of machines supporting multiple page sizes
and on these machines the host and a guest can be running, each one,
with a different page size.

For what pertains to virtio-gpu, this is not a problem if the page size
of the guest happens to be bigger or equal than the host, but will
potentially lead to failures in memory allocations and/or mappings
otherwise.

To deal with this, the virtio-spec was extended to introduce with the
VIRTIO_GPU_F_BLOB_ALIGNMENT feature [1]. If this feature is negotiated,
we must use the "blob_alignment" field in the config to ensure every
CREATE_BLOB and MAP_BLOB is properly aligned before sending it to the
device.

We also introduce the VIRTGPU_PARAM_BLOB_ALIGNMENT parameter to allow
userspace to query the alignment restrictions for blobs.

This supersedes "drm/virtio: introduce the HOST_PAGE_SIZE feature" [2].

[1] https://github.com/oasis-tcs/virtio-spec/commit/f9abfd55cb663837dda1153b826216dcf4d25b84
[2] https://lkml.org/lkml/2024/7/23/438

Changes in v2:
- Rebased.
- Moved blob size alignment validation to verify_blob(), rejecting
misaligned sizes early in the ioctl path instead of checking in
virtio_gpu_cmd_resource_create_blob() and virtio_gpu_cmd_map()
(Dmitry Osipenko).

Sergio Lopez (3):
  drm/virtio: support VIRTIO_GPU_F_BLOB_ALIGNMENT
  drm/virtio: honor blob_alignment requirements
  drm/virtio: add VIRTGPU_PARAM_BLOB_ALIGNMENT to params

 drivers/gpu/drm/virtio/virtgpu_drv.c   |  1 +
 drivers/gpu/drm/virtio/virtgpu_drv.h   |  2 ++
 drivers/gpu/drm/virtio/virtgpu_ioctl.c | 10 ++++++++++
 drivers/gpu/drm/virtio/virtgpu_kms.c   | 14 +++++++++++---
 include/uapi/drm/virtgpu_drm.h         |  1 +
 include/uapi/linux/virtio_gpu.h        |  9 +++++++++
 6 files changed, 34 insertions(+), 3 deletions(-)

-- 
2.53.0

[PATCH v2 1/3] drm/virtio: support VIRTIO_GPU_F_BLOB_ALIGNMENT

[Sergio Lopez]

Support VIRTIO_GPU_F_BLOB_ALIGNMENT, a feature that indicates the device
provides a valid blob_alignment field in its configuration, and that
both RESOURCE_CREATE_BLOB and RESOURCE_MAP_BLOB requests must be aligned
to that value.

Signed-off-by: Sergio Lopez <slp@redhat.com>
---
 drivers/gpu/drm/virtio/virtgpu_drv.c |  1 +
 drivers/gpu/drm/virtio/virtgpu_drv.h |  2 ++
 drivers/gpu/drm/virtio/virtgpu_kms.c | 14 +++++++++++---
 include/uapi/linux/virtio_gpu.h      |  9 +++++++++
 4 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.c b/drivers/gpu/drm/virtio/virtgpu_drv.c
index a5ce96fb8a1d..812ee3f5e4aa 100644
--- a/drivers/gpu/drm/virtio/virtgpu_drv.c
+++ b/drivers/gpu/drm/virtio/virtgpu_drv.c
@@ -163,6 +163,7 @@ static unsigned int features[] = {
 	VIRTIO_GPU_F_RESOURCE_UUID,
 	VIRTIO_GPU_F_RESOURCE_BLOB,
 	VIRTIO_GPU_F_CONTEXT_INIT,
+	VIRTIO_GPU_F_BLOB_ALIGNMENT,
 };
 static struct virtio_driver virtio_gpu_driver = {
 	.feature_table = features,
diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h b/drivers/gpu/drm/virtio/virtgpu_drv.h
index f17660a71a3e..d1fa386a5a99 100644
--- a/drivers/gpu/drm/virtio/virtgpu_drv.h
+++ b/drivers/gpu/drm/virtio/virtgpu_drv.h
@@ -257,6 +257,7 @@ struct virtio_gpu_device {
 	bool has_resource_blob;
 	bool has_host_visible;
 	bool has_context_init;
+	bool has_blob_alignment;
 	struct virtio_shm_region host_visible_region;
 	struct drm_mm host_visible_mm;
 
@@ -270,6 +271,7 @@ struct virtio_gpu_device {
 	uint32_t num_capsets;
 	uint64_t capset_id_mask;
 	struct list_head cap_cache;
+	uint32_t blob_alignment;
 
 	/* protects uuid state when exporting */
 	spinlock_t resource_export_lock;
diff --git a/drivers/gpu/drm/virtio/virtgpu_kms.c b/drivers/gpu/drm/virtio/virtgpu_kms.c
index 80ba69b4860b..cfde9f573df6 100644
--- a/drivers/gpu/drm/virtio/virtgpu_kms.c
+++ b/drivers/gpu/drm/virtio/virtgpu_kms.c
@@ -124,7 +124,7 @@ int virtio_gpu_init(struct virtio_device *vdev, struct drm_device *dev)
 	struct virtio_gpu_device *vgdev;
 	/* this will expand later */
 	struct virtqueue *vqs[2];
-	u32 num_scanouts, num_capsets;
+	u32 num_scanouts, num_capsets, blob_alignment;
 	int ret = 0;
 
 	if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1))
@@ -198,14 +198,22 @@ int virtio_gpu_init(struct virtio_device *vdev, struct drm_device *dev)
 	if (virtio_has_feature(vgdev->vdev, VIRTIO_GPU_F_CONTEXT_INIT))
 		vgdev->has_context_init = true;
 
+	if (virtio_has_feature(vgdev->vdev, VIRTIO_GPU_F_BLOB_ALIGNMENT)) {
+		vgdev->has_blob_alignment = true;
+		virtio_cread_le(vgdev->vdev, struct virtio_gpu_config,
+				blob_alignment, &blob_alignment);
+		vgdev->blob_alignment = blob_alignment;
+	}
+
 	DRM_INFO("features: %cvirgl %cedid %cresource_blob %chost_visible",
 		 vgdev->has_virgl_3d    ? '+' : '-',
 		 vgdev->has_edid        ? '+' : '-',
 		 vgdev->has_resource_blob ? '+' : '-',
 		 vgdev->has_host_visible ? '+' : '-');
 
-	DRM_INFO("features: %ccontext_init\n",
-		 vgdev->has_context_init ? '+' : '-');
+	DRM_INFO("features: %ccontext_init %cblob_alignment\n",
+		 vgdev->has_context_init ? '+' : '-',
+		 vgdev->has_blob_alignment ? '+' : '-');
 
 	ret = virtio_find_vqs(vgdev->vdev, 2, vqs, vqs_info, NULL);
 	if (ret) {
diff --git a/include/uapi/linux/virtio_gpu.h b/include/uapi/linux/virtio_gpu.h
index be109777d10d..4f530d90058c 100644
--- a/include/uapi/linux/virtio_gpu.h
+++ b/include/uapi/linux/virtio_gpu.h
@@ -64,6 +64,14 @@
  * context_init and multiple timelines
  */
 #define VIRTIO_GPU_F_CONTEXT_INIT        4
+/*
+ * The device provides a valid blob_alignment
+ * field in its configuration and both
+ * VIRTIO_GPU_CMD_RESOURCE_CREATE_BLOB and
+ * VIRTIO_GPU_CMD_RESOURCE_MAP_BLOB requests
+ * must be aligned to that value.
+ */
+#define VIRTIO_GPU_F_BLOB_ALIGNMENT      5
 
 enum virtio_gpu_ctrl_type {
 	VIRTIO_GPU_UNDEFINED = 0,
@@ -365,6 +373,7 @@ struct virtio_gpu_config {
 	__le32 events_clear;
 	__le32 num_scanouts;
 	__le32 num_capsets;
+	__le32 blob_alignment;
 };
 
 /* simple formats for fbcon/X use */
-- 
2.53.0

[PATCH v2 2/3] drm/virtio: honor blob_alignment requirements

[Sergio Lopez]

If VIRTIO_GPU_F_BLOB_ALIGNMENT has been negotiated, blob size must be
aligned to blob_alignment. Validate this in verify_blob() so that
invalid requests are rejected early.

Signed-off-by: Sergio Lopez <slp@redhat.com>
---
 drivers/gpu/drm/virtio/virtgpu_ioctl.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
index c33c057365f8..d0c4edf1eaf4 100644
--- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
+++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
@@ -489,6 +489,11 @@ static int verify_blob(struct virtio_gpu_device *vgdev,
 	params->size = rc_blob->size;
 	params->blob = true;
 	params->blob_flags = rc_blob->blob_flags;
+
+	if (vgdev->has_blob_alignment &&
+	    !IS_ALIGNED(params->size, vgdev->blob_alignment))
+		return -EINVAL;
+
 	return 0;
 }
 
-- 
2.53.0

Re: [PATCH v2 2/3] drm/virtio: honor blob_alignment requirements

[Alyssa Ross]

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On Tue, Apr 28, 2026 at 09:44:49PM +0200, Sergio Lopez wrote:
> If VIRTIO_GPU_F_BLOB_ALIGNMENT has been negotiated, blob size must be
> aligned to blob_alignment. Validate this in verify_blob() so that
> invalid requests are rejected early.
>
> Signed-off-by: Sergio Lopez <slp@redhat.com>

FYI: this change breaks crosvm, which is squatting the 5 and 6 values
of VIRTIO_GPU_F_* with different meanings.  I've reported it as a
crosvm bug, so hopefully it can be taken care of there.

https://issuetracker.google.com/issues/529852979

> ---
>  drivers/gpu/drm/virtio/virtgpu_ioctl.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> index c33c057365f8..d0c4edf1eaf4 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> @@ -489,6 +489,11 @@ static int verify_blob(struct virtio_gpu_device *vgdev,
>  	params->size = rc_blob->size;
>  	params->blob = true;
>  	params->blob_flags = rc_blob->blob_flags;
> +
> +	if (vgdev->has_blob_alignment &&
> +	    !IS_ALIGNED(params->size, vgdev->blob_alignment))
> +		return -EINVAL;
> +
>  	return 0;
>  }
>
> --
> 2.53.0
>

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Re: [PATCH v2 2/3] drm/virtio: honor blob_alignment requirements

[Michael S. Tsirkin]

On Wed, Jul 01, 2026 at 01:10:30PM +0200, Alyssa Ross wrote:
> On Tue, Apr 28, 2026 at 09:44:49PM +0200, Sergio Lopez wrote:
> > If VIRTIO_GPU_F_BLOB_ALIGNMENT has been negotiated, blob size must be
> > aligned to blob_alignment. Validate this in verify_blob() so that
> > invalid requests are rejected early.
> >
> > Signed-off-by: Sergio Lopez <slp@redhat.com>
> 
> FYI: this change breaks crosvm, which is squatting the 5 and 6 values
> of VIRTIO_GPU_F_* with different meanings.  I've reported it as a
> crosvm bug, so hopefully it can be taken care of there.
> 
> https://issuetracker.google.com/issues/529852979

Move fast and beak things, then it takes a wile to fix them)
Do you understand who uses it maybe? Maybe if there's a PR
for both sides it will be handled faster.

> > ---
> >  drivers/gpu/drm/virtio/virtgpu_ioctl.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> > index c33c057365f8..d0c4edf1eaf4 100644
> > --- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> > +++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> > @@ -489,6 +489,11 @@ static int verify_blob(struct virtio_gpu_device *vgdev,
> >  	params->size = rc_blob->size;
> >  	params->blob = true;
> >  	params->blob_flags = rc_blob->blob_flags;
> > +
> > +	if (vgdev->has_blob_alignment &&
> > +	    !IS_ALIGNED(params->size, vgdev->blob_alignment))
> > +		return -EINVAL;
> > +
> >  	return 0;
> >  }
> >
> > --
> > 2.53.0
> >

Re: [PATCH v2 2/3] drm/virtio: honor blob_alignment requirements

[Alyssa Ross]

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"Michael S. Tsirkin" <mst@redhat.com> writes:

> On Wed, Jul 01, 2026 at 01:10:30PM +0200, Alyssa Ross wrote:
>> On Tue, Apr 28, 2026 at 09:44:49PM +0200, Sergio Lopez wrote:
>> > If VIRTIO_GPU_F_BLOB_ALIGNMENT has been negotiated, blob size must be
>> > aligned to blob_alignment. Validate this in verify_blob() so that
>> > invalid requests are rejected early.
>> >
>> > Signed-off-by: Sergio Lopez <slp@redhat.com>
>> 
>> FYI: this change breaks crosvm, which is squatting the 5 and 6 values
>> of VIRTIO_GPU_F_* with different meanings.  I've reported it as a
>> crosvm bug, so hopefully it can be taken care of there.
>> 
>> https://issuetracker.google.com/issues/529852979
>
> Move fast and beak things, then it takes a wile to fix them)
> Do you understand who uses it maybe? Maybe if there's a PR
> for both sides it will be handled faster.

I have no idea where the device side is.  Doesn't seem to be in the
Chromium kernel tree, nor are there any patches for it in Chromium
Gerrit.  Maybe Gurchetan can shed some light?

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[PATCH v2 3/3] drm/virtio: add VIRTGPU_PARAM_BLOB_ALIGNMENT to params

[Sergio Lopez]

Add VIRTGPU_PARAM_BLOB_ALIGNMENT as a param that can be read with
VIRTGPU_GETPARAM by userspace applications running in the guest to
obtain the host's page size and find out the right alignment to be used
in shared memory allocations.

Signed-off-by: Sergio Lopez <slp@redhat.com>
---
 drivers/gpu/drm/virtio/virtgpu_ioctl.c | 5 +++++
 include/uapi/drm/virtgpu_drm.h         | 1 +
 2 files changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
index d0c4edf1eaf4..146ff25396c2 100644
--- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
+++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
@@ -117,6 +117,11 @@ static int virtio_gpu_getparam_ioctl(struct drm_device *dev, void *data,
 	case VIRTGPU_PARAM_EXPLICIT_DEBUG_NAME:
 		value = vgdev->has_context_init ? 1 : 0;
 		break;
+	case VIRTGPU_PARAM_BLOB_ALIGNMENT:
+		if (!vgdev->has_blob_alignment)
+			return -ENOENT;
+		value = vgdev->blob_alignment;
+		break;
 	default:
 		return -EINVAL;
 	}
diff --git a/include/uapi/drm/virtgpu_drm.h b/include/uapi/drm/virtgpu_drm.h
index 9debb320c34b..7d4e4884d942 100644
--- a/include/uapi/drm/virtgpu_drm.h
+++ b/include/uapi/drm/virtgpu_drm.h
@@ -98,6 +98,7 @@ struct drm_virtgpu_execbuffer {
 #define VIRTGPU_PARAM_CONTEXT_INIT 6 /* DRM_VIRTGPU_CONTEXT_INIT */
 #define VIRTGPU_PARAM_SUPPORTED_CAPSET_IDs 7 /* Bitmask of supported capability set ids */
 #define VIRTGPU_PARAM_EXPLICIT_DEBUG_NAME 8 /* Ability to set debug name from userspace */
+#define VIRTGPU_PARAM_BLOB_ALIGNMENT 9 /* Device alignment requirements for blobs */
 
 struct drm_virtgpu_getparam {
 	__u64 param;
-- 
2.53.0

Re: [PATCH v2 0/3] drm/virtio: introduce F_BLOB_ALIGNMENT support

[Dmitry Osipenko]

On 4/28/26 22:44, Sergio Lopez wrote:
> There's an increasing number of machines supporting multiple page sizes
> and on these machines the host and a guest can be running, each one,
> with a different page size.
> 
> For what pertains to virtio-gpu, this is not a problem if the page size
> of the guest happens to be bigger or equal than the host, but will
> potentially lead to failures in memory allocations and/or mappings
> otherwise.
> 
> To deal with this, the virtio-spec was extended to introduce with the
> VIRTIO_GPU_F_BLOB_ALIGNMENT feature [1]. If this feature is negotiated,
> we must use the "blob_alignment" field in the config to ensure every
> CREATE_BLOB and MAP_BLOB is properly aligned before sending it to the
> device.
> 
> We also introduce the VIRTGPU_PARAM_BLOB_ALIGNMENT parameter to allow
> userspace to query the alignment restrictions for blobs.
> 
> This supersedes "drm/virtio: introduce the HOST_PAGE_SIZE feature" [2].
> 
> [1] https://github.com/oasis-tcs/virtio-spec/commit/f9abfd55cb663837dda1153b826216dcf4d25b84
> [2] https://lkml.org/lkml/2024/7/23/438
> 
> Changes in v2:
> - Rebased.
> - Moved blob size alignment validation to verify_blob(), rejecting
> misaligned sizes early in the ioctl path instead of checking in
> virtio_gpu_cmd_resource_create_blob() and virtio_gpu_cmd_map()
> (Dmitry Osipenko).
> 
> Sergio Lopez (3):
>   drm/virtio: support VIRTIO_GPU_F_BLOB_ALIGNMENT
>   drm/virtio: honor blob_alignment requirements
>   drm/virtio: add VIRTGPU_PARAM_BLOB_ALIGNMENT to params
> 
>  drivers/gpu/drm/virtio/virtgpu_drv.c   |  1 +
>  drivers/gpu/drm/virtio/virtgpu_drv.h   |  2 ++
>  drivers/gpu/drm/virtio/virtgpu_ioctl.c | 10 ++++++++++
>  drivers/gpu/drm/virtio/virtgpu_kms.c   | 14 +++++++++++---
>  include/uapi/drm/virtgpu_drm.h         |  1 +
>  include/uapi/linux/virtio_gpu.h        |  9 +++++++++
>  6 files changed, 34 insertions(+), 3 deletions(-)
> 

Applied to misc-next, thanks

-- 
Best regards,
Dmitry