Re: [PATCH v2] drm/virtio: do not enforce blob_alignment in cross-domain contexts

[Dmitry Osipenko]

On 10/6/26 18:42, Val Packett wrote:
> VIRTIO_GPU_F_BLOB_ALIGNMENT is designed for GPU rendering context types,
> however VIRTIO_GPU_CAPSET_CROSS_DOMAIN is not one of those. Resources
> created under cross-domain contexts are arbitrary shared system memory
> files, which includes unusual things like Wayland keymaps received
> from the host compositor. Do not enforce alignment requirements there.
> 
> Fixes: 47248e0d8264 ("drm/virtio: honor blob_alignment requirements")
> Signed-off-by: Val Packett <val@xxxxxxxxxxxxxxxxxxxxxx>
> ---
> 
> v2: also check has_virgl_3d to prevent dereferencing NULL vfpriv
> v1: https://lore.kernel.org/all/20261006004044.2242154-1-val@xxxxxxxxxxxxxxxxxxxxxx/
> 
> ~val
> 
> ---
>  drivers/gpu/drm/virtio/virtgpu_ioctl.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> index 3ddd5481d6bc..4d5ae062834d 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> @@ -551,7 +551,9 @@ static int verify_blob(struct virtio_gpu_device *vgdev,
>  	params->blob_flags = rc_blob->blob_flags;
>  	params->blob_hints = rc_blob->blob_hints;
>  
> -	if (vgdev->has_blob_alignment &&
> +	if (vgdev->has_blob_alignment && vgdev->has_virgl_3d &&
> +	    (vfpriv->context_init & VIRTIO_GPU_CONTEXT_INIT_CAPSET_ID_MASK) !=
> +	    VIRTIO_GPU_CAPSET_CROSS_DOMAIN &&
>  	    !IS_ALIGNED(params->size, vgdev->blob_alignment))
>  		return -EINVAL;
>  

What userspace has this problem and why it re-purposes virtio-gpu to act
as udmabuf for arbitrary data that never reaches host?

-- 
Best regards,
Dmitry