drm/virtio: not pin pages on demand

[Chia-I Wu]

On Thu, Oct 21, 2021 at 4:52 AM Gerd Hoffmann <kraxel at redhat.com> wrote:
>
> On Thu, Oct 21, 2021 at 11:55:47AM +0200, Maksym Wezdecki wrote:
> > I get your point. However, we need to make resource_create ioctl,
> > in order to create corresponding resource on the host.
>
> That used to be the case but isn't true any more with the new
> blob resources.  virglrenderer allows to create gpu objects
> via execbuffer.  Those gpu objects can be linked to a
> virtio-gpu resources, but it's optional.  In your case you
> would do that only for your staging buffer.  The other textures
> (which you fill with a host-side copy from the staging buffer)
> do not need a virtio-gpu resource in the first place.
That's however a breaking change to the virgl protocol.  All virgl
commands expect res ids rather than blob ids.

Using VIRTGPU_BLOB_MEM_HOST3D could in theory work.  But there are a
few occasions where virglrenderer expects there to be guest storage.
There are also readbacks that we need to support.  We might end up
using VIRTGPU_BLOB_MEM_HOST3D_GUEST, where pin-on-demand is still
desirable.

For this patch, I think the uapi change can be simplified.  It can be
a new param plus a new field in drm_virtgpu_execbuffer

  __u64 bo_flags; /* pointer to an array of size num_bo_handles, or NULL */

The other changes do not seem needed.

>
> take care,
>   Gerd
>