Help debug amdgpu faults

[Khatri, Sunil]

[AMD Official Use Only - General]

Hello Alex, Robert

I too have similar issues which I am facing on chrome. Are there any tools in linux environment which can help debug such issues like page faults, kernel panic caused by invalid pointer access.

I have used tools like ramdump parser which can be used to use the ramdump after a crash and check a lot of static data in the memory and even the page table could be checked by walking through them manually. We used to load the kernel symbols along with ramdump to go line by line.

Appreciate if you can point to some document or some tools which is already used by linux graphics teams either UMD or KMD drivers so chrome team can also exploit those to debug issues.

Regards
Sunil Khatri 

-----Original Message-----
From: amd-gfx <amd-gfx-bounces at lists.freedesktop.org> On Behalf Of Alex Deucher
Sent: Tuesday, November 22, 2022 7:42 PM
To: Robert Beckett <bob.beckett at collabora.com>
Cc: Dmitrii Osipenko <dmitry.osipenko at collabora.com>; Adrián Martínez Larumbe <adrian.larumbe at collabora.com>; Koenig, Christian <Christian.Koenig at amd.com>; amd-gfx at lists.freedesktop.org; Daniel Stone <daniels at collabora.com>
Subject: Re: Help debug amdgpu faults

On Tue, Nov 22, 2022 at 6:53 AM Robert Beckett <bob.beckett at collabora.com> wrote:
>
> Hi,
>
>
> does anyone know any documentation, or can provide advice on debugging amdgpu fault reports?

This is a GPU page fault so it refers the the GPU virtual address space of the application .  Each process (well fd really), gets its own GPU virtual address space into which system memory, system mmio space, or vram can be mapped.  The user mode drivers control their GPU virtual address space.

>
>
> e.g:
>
> Nov 21 19:17:06 fedora kernel: amdgpu 0000:01:00.0: amdgpu: [gfxhub] 
> page fault (src_id:0 ring:8 vmid:1 pasid:32769, for process vkcube pid 
> 999 thread vkcube pid 999)

This is the process that caused the fault.

> Nov 21 19:17:06 fedora kernel: amdgpu 0000:01:00.0: amdgpu:   in page starting at address 0x0000800100700000 from client 0x1b (UTCL2)

This is the virtual address that faulted.

> Nov 21 19:17:06 fedora kernel: amdgpu 0000:01:00.0: amdgpu: GCVM_L2_PROTECTION_FAULT_STATUS:0x00101A10
> Nov 21 19:17:06 fedora kernel: amdgpu 0000:01:00.0: amdgpu:          Faulty UTCL2 client ID: SDMA0 (0xd)

The fault came from the SDMA engine.

> Nov 21 19:17:06 fedora kernel: amdgpu 0000:01:00.0: amdgpu:          MORE_FAULTS: 0x0
> Nov 21 19:17:06 fedora kernel: amdgpu 0000:01:00.0: amdgpu:          WALKER_ERROR: 0x0
> Nov 21 19:17:06 fedora kernel: amdgpu 0000:01:00.0: amdgpu:          PERMISSION_FAULTS: 0x1

The page was not marked as valid in the GPU page table.

> Nov 21 19:17:06 fedora kernel: amdgpu 0000:01:00.0: amdgpu:          MAPPING_ERROR: 0x0
> Nov 21 19:17:06 fedora kernel: amdgpu 0000:01:00.0: amdgpu:          RW: 0x0

SDMA attempted to read an invalid page.

>
>
>
> see https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.freedesktop.org%2Fdrm%2Famd%2F-%2Fissues%2F2267&data=05%7C01%7Csunil.khatri%40amd.com%7Cd7778c40bff6443c2af708dacc9394c6%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638047231486449634%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=vep6PKgDjRz02A3xYI8f7600QV2%2B7GYXsx%2FVYPY1M2I%3D&reserved=0 for more context.
>
> We have a complicated setup involving rendering then blitting to virtio-gpu exported dmabufs, with plenty of hacks in the mesa and xwayland stacks, so we are considering this our issue to debug, and not an issue with the driver at this point.
> However, having debugged all the interesting parts leading to these faults, I am unable to decode the fault report to correlate to a buffer.
>
> in the fault report, what address space is the address from?
> given that the fault handler shifts the reported addres up by 12, I assume it is a 4K pfn which makes me assume a physical address is this correct?
> if so, is that a vram pa or a host system memory pa?
> is there any documentation for the other fields reported like the fault status etc?

See the comments above.  There is some kernel doc as well:
https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdocs.kernel.org%2Fgpu%2Famdgpu%2Fdriver-core.html%23amdgpu-virtual-memory&data=05%7C01%7Csunil.khatri%40amd.com%7Cd7778c40bff6443c2af708dacc9394c6%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638047231486449634%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=dd971OoEZSJl%2FJif4%2Bypv9Dp0deeMVsQuCMc2o9BgQk%3D&reserved=0

>
> I'd appreciate any advice you could give to help us debug further.

Some operation you are doing in the user mode driver is reading an invalid page.  Possibly reading past the end of a buffer or something mis-aligned.  Compare the faulting GPU address to the GPU virtual address space in the application and you should be able to track down what is happening.

Alex

>
> Thanks
>
> Bob
>
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