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

[Robert Beckett <bob.beckett@xxxxxxxxxxxxx>]

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