Various problems trying to vga-passthrough a Renoir iGPU to a xen/qubes-os hvm

[Alex Deucher]

On Mon, Dec 6, 2021 at 4:36 PM Yann Dirson <ydirson at free.fr> wrote:
>
> Hi Alex,
>
> > We have not validated virtualization of our integrated GPUs.  I don't
> > know that it will work at all.  We had done a bit of testing but ran
> > into the same issues with the PSP, but never had a chance to debug
> > further because this feature is not productized.
> ...
> > You need a functional PSP to get the GPU driver up and running.
>
> Ah, thanks for the hint :)
>
> I guess that if I want to have any chance to get the PSP working I'm
> going to need more details on it.  A quick search some time ago mostly
> brought reverse-engineering work, rather than official AMD doc.  Are
> there some AMD resources I missed ?

The driver code is pretty much it.  On APUs, the PSP is shared with
the CPU and the rest of the platform.  The GPU driver just interacts
with it for a few specific tasks:
1. Loading Trusted Applications (e.g., trusted firmware applications
that run on the PSP for specific functionality, e.g., HDCP and content
protection, etc.)
2. Validating and loading firmware for other engines on the SoC.  This
is required to use those engines.

I'm not too familiar with the PSP's path to memory from the GPU
perspective.  IIRC, most memory used by the PSP goes through carve out
"vram" on APUs so it should work, but I would double check if there
are any system memory allocations that used to interact with the PSP
and see if changing them to vram helps.  It does work with the IOMMU
enabled on bare metal, so it should work in passthrough as well in
theory.

Alex


>
> Best regards,
> --
> Yann