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

[Gurchetan Singh <gurchetansingh@xxxxxxxxxxxx>]

On Tue, Apr 6, 2021 at 1:47 PM Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx> 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@xxxxxxxxxx>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx>
---
 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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