Re: [PATCH v5 0/8] Support virtio-gpu DRM native context

[Dmitry Osipenko]

On 1/23/25 14:58, Alex Bennée wrote:
> Dmitry Osipenko <dmitry.osipenko@collabora.com> writes:
> 
>> On 1/22/25 20:00, Alex Bennée wrote:
>>> Dmitry Osipenko <dmitry.osipenko@collabora.com> writes:
>>>
>>>> This patchset adds DRM native context support to VirtIO-GPU on Qemu.
>>>>
>>>> Contarary to Virgl and Venus contexts that mediates high level GFX APIs,
>>>> DRM native context [1] mediates lower level kernel driver UAPI, which
>>>> reflects in a less CPU overhead and less/simpler code needed to support it.
>>>> DRM context consists of a host and guest parts that have to be implemented
>>>> for each GPU driver. On a guest side, DRM context presents a virtual GPU as
>>>> a real/native host GPU device for GL/VK applications.
>>>>
>>>> [1] https://www.youtube.com/watch?v=9sFP_yddLLQ
>>>>
>>>> Today there are four known DRM native context drivers existing in a wild:
>>>>
>>>>   - Freedreno (Qualcomm SoC GPUs), completely upstreamed
>>>>   - AMDGPU, mostly merged into upstreams
>>>
>>> I tried my AMD system today with:
>>>
>>> Host:
>>>   Aarch64 AVA system
>>>   Trixie
>>>   virglrenderer @ v1.1.0/99557f5aa130930d11f04ffeb07f3a9aa5963182
>>>   -display sdl,gl=on (gtk,gl=on also came up but handled window resizing
>>>   poorly)
>>>   
>>> KVM Guest
>>>
>>>   Aarch64
>>>   Trixie
>>>   mesa @ main/d27748a76f7dd9236bfcf9ef172dc13b8c0e170f
>>>   -Dvulkan-drivers=virtio,amd -Dgallium-drivers=virgl,radeonsi 
>>> -Damdgpu-virtio=true
>>>
>>> However when I ran vulkan-info --summary KVM faulted with:
>>>
>>>   debian-trixie login: error: kvm run failed Bad address
>>>    PC=0000ffffb9aa1eb0 X00=0000ffffba0450a4 X01=0000aaaaf7f32400
>>>   X02=000000000000013c X03=0000ffffba045098 X04=0000aaaaf7f3253c
>>>   X05=0000ffffba0451d4 X06=00000000c0016900 X07=000000000000000e
>>>   X08=0000000000000014 X09=00000000000000ff X10=0000aaaaf7f32500
>>>   X11=0000aaaaf7e4d028 X12=0000aaaaf7edbcb0 X13=0000000000000001
>>>   X14=000000000000000c X15=0000000000007718 X16=0000ffffb93601f0
>>>   X17=0000ffffb9aa1dc0 X18=00000000000076f0 X19=0000aaaaf7f31330
>>>   X20=0000aaaaf7f323f0 X21=0000aaaaf7f235e0 X22=000000000000004c
>>>   X23=0000aaaaf7f2b5e0 X24=0000aaaaf7ee0cb0 X25=00000000000000ff
>>>   X26=0000000000000076 X27=0000ffffcd2b18a8 X28=0000aaaaf7ee0cb0
>>>   X29=0000ffffcd2b0bd0 X30=0000ffffb86c8b98  SP=0000ffffcd2b0bd0
>>>   PSTATE=20001000 --C- EL0t
>>>   QEMU 9.2.50 monitor - type 'help' for more information
>>>   (qemu) quit
>>>
>>> Which looks very much like the PFN locking failure. However booting up
>>> with venus=on instead works. Could there be any differences in the way
>>> device memory is mapped in the two cases?
>>
>> Memory mapping works exactly the same for nctx and venus. Are you on
>> 6.13 host kernel?
> 
> Yes - with the Altra PCI workaround patches on both host and guest
> kernel.
> 
> Is there anyway to trace the sharing of device memory on the host so I
> can verify its an attempt at device access? The PC looks like its in
> user-space but once this fails the guest is suspended so I can't poke
> around in its environment.

I'm adding printk's to kernel in a such cases. Likely there is no other
better way to find why it fails.

Does your ARM VM and host both use 4k page size?

Well, if it's a page refcounting bug on ARM/KMV, then applying [1] to
the host driver will make it work and we will know where the problem is.
Please try.

[1]
https://patchwork.kernel.org/project/kvm/patch/20220815095423.11131-1-dmitry.osipenko@collabora.com/

-- 
Best regards,
Dmitry