Re: [PATCH] drm/virtio: Create Dumb BOs as guest Blobs (v2)

[Gurchetan Singh <gurchetansingh@chromium.org>]

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On Tue, Apr 6, 2021 at 1:47 PM Vivek Kasireddy <vivek.kasireddy@intel.com>
wrote:

> If support for Blob resources is available, then dumb BOs created
> by the driver can be considered as guest Blobs.
>
> v2: Don't skip transfer and flush commands as part of plane update
> as the device may have created a shared mapping. (Gerd)
>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
> ---
>  drivers/gpu/drm/virtio/virtgpu_gem.c    | 8 ++++++++
>  drivers/gpu/drm/virtio/virtgpu_object.c | 3 +++
>  2 files changed, 11 insertions(+)
>
> diff --git a/drivers/gpu/drm/virtio/virtgpu_gem.c
> b/drivers/gpu/drm/virtio/virtgpu_gem.c
> index 8502400b2f9c..5f49fb1cce65 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_gem.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_gem.c
> @@ -64,6 +64,7 @@ int virtio_gpu_mode_dumb_create(struct drm_file
> *file_priv,
>  {
>         struct drm_gem_object *gobj;
>         struct virtio_gpu_object_params params = { 0 };
> +       struct virtio_gpu_device *vgdev = dev->dev_private;
>         int ret;
>         uint32_t pitch;
>
> @@ -79,6 +80,13 @@ int virtio_gpu_mode_dumb_create(struct drm_file
> *file_priv,
>         params.height = args->height;
>         params.size = args->size;
>         params.dumb = true;
> +
> +       if (vgdev->has_resource_blob) {
> +               params.blob_mem = VIRTGPU_BLOB_MEM_GUEST;
> +               params.blob_flags = VIRTGPU_BLOB_FLAG_USE_SHAREABLE;
>

This creates some log spam with crosvm + virgl_3d + vanilla linux, since
transfers don't work for guest blobs.  Two options:

a) Add vgdev->has_virgl_3d check and don't create a guest blob in that case.
b) The interactions between TRANSFER_TO_HOST_2D and VIRTGPU_BLOB_MEM_GUEST
are a bit under-defined in the spec.  Though since you don't have a host
side resource, you can safely skip the transfer and crosvm can be modified
to do the right thing in case of RESOURCE_FLUSH.

It makes a ton of sense to have a explicit udmabuf-like flag
("BLOB_FLAG_CREATE_GUEST_HANDLE" or "BLOB_FLAG_HANDLE_FROM_GUEST" -- want
to host OS agnostic -- any other ideas?), especially with 3d mode.  For
now, implicit udmabuf + dumb should be fine since the QEMU patches have
been floating around for a while and should land soon for future use cases.



> +               params.blob = true;
> +       }
>



> +
>         ret = virtio_gpu_gem_create(file_priv, dev, &params, &gobj,
>                                     &args->handle);
>         if (ret)
> diff --git a/drivers/gpu/drm/virtio/virtgpu_object.c
> b/drivers/gpu/drm/virtio/virtgpu_object.c
> index 4ff1ec28e630..f648b0e24447 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_object.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_object.c
> @@ -254,6 +254,9 @@ int virtio_gpu_object_create(struct virtio_gpu_device
> *vgdev,
>         }
>
>         if (params->blob) {
> +               if (params->blob_mem == VIRTGPU_BLOB_MEM_GUEST)
> +                       bo->guest_blob = true;
> +
>                 virtio_gpu_cmd_resource_create_blob(vgdev, bo, params,
>                                                     ents, nents);
>         } else if (params->virgl) {
> --
> 2.26.2
>
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>

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