Re: [QEMU PATCH 1/1] virtgpu: do not destroy resources when guest suspend

["Kim, Dongwon" <dongwon.kim@xxxxxxxxx>]

Hello,

I just came across this discussion regarding s3/s4 support in virtio-gpu 
driver and QEMU.
We saw similar problem a while ago (QEMU deletes all objects upon 
suspension) and
came up with an experimental solution that is basically making 
virtio-gpu driver to do object creation
for all existing resources once VM is resumed so that he QEMU recreate them.

This method has worked pretty well on our case. I submitted patches for 
this to dri-devel a while ago.
[RFC PATCH 0/2] drm/virtio:virtio-gpu driver freeze-and-restore 
implementation (lists.freedesktop.org) 
<https://lists.freedesktop.org/archives/dri-devel/2022-September/373892.html>
This is kernel driver only solution. Nothing has to be changed in QEMU.

Jiqian and other reviewers, can you check this old solution we suggested 
as well?
On 6/20/2023 5:26 AM, Robert Beckett wrote:

> On 20/06/2023 10:41, Gerd Hoffmann wrote:
> >    Hi,
> >
> > > > The guest driver should be able to restore resources after resume.
> > > Thank you for your suggestion!
> > > As far as I know, resources are created on host side and guest has 
> > > no backup, if resources are destroyed, guest can't restore them.
> > > Or do you mean guest driver need to send commands to re-create 
> > > resources after resume?
> > The later.  The guest driver knows which resources it has created,
> > it can restore them after suspend.
>
> Are you sure that this is viable?
>
> How would you propose that a guest kernel could reproduce a resource, 
> including pixel data upload during a resume?
> The kernel would not have any of the pixel data to transfer to host. 
> This is normally achieved by guest apps calling GL calls and mesa 
> asking the kernel to create the textures with the given data (often 
> read from a file).
> If your suggestion is to get the userland application to do it, that 
> would entirely break how suspend/resume is meant to happen. It should 
> be transparent to userland applications for the most part.
> Could you explain how you anticipate the guest being able to reproduce 
> the resources please?
>
> > > If so, I have some questions. Can guest re-create resources by using
> > > object(virtio_vpu_object) or others? Can the new resources replace the
> > > destroyed resources to continue the suspended display tasks after
> > > resume?
> > Any display scanout information will be gone too, the guest driver needs
> > re-create this too (after re-creating the resources).
> >
> > take care,
> >    Gerd