linux-kernel - Re: commit 7ffb791423c7 breaks steam game

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Message-ID: <76672910-423c-4664-a1bd-da5c1d7d6afd@nvidia.com>
Date: Wed, 26 Mar 2025 10:43:27 +1100
From: Balbir Singh <balbirs@...dia.com>
To: Bert Karwatzki <spasswolf@....de>,
 Christian König <christian.koenig@....com>
Cc: Ingo Molnar <mingo@...nel.org>, Kees Cook <kees@...nel.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 Peter Zijlstra <peterz@...radead.org>, Andy Lutomirski <luto@...nel.org>,
 Alex Deucher <alexander.deucher@....com>, linux-kernel@...r.kernel.org,
 amd-gfx@...ts.freedesktop.org
Subject: Re: commit 7ffb791423c7 breaks steam game

On 3/26/25 10:21, Bert Karwatzki wrote:
> Am Mittwoch, dem 26.03.2025 um 09:45 +1100 schrieb Balbir Singh:
>>
>>
>> The second region seems to be additional, I suspect that is HMM mapping from kgd2kfd_init_zone_device()
>>
>> Balbir Singh
>>
> Good guess! I inserted a printk into kgd2kfd_init_zone_device():
> 
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> index d05d199b5e44..201220e2ac42 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> @@ -1049,6 +1049,8 @@ int kgd2kfd_init_zone_device(struct amdgpu_device *adev)
>                 pgmap->range.end = res->end;
>                 pgmap->type = MEMORY_DEVICE_PRIVATE;
>         }
> +       dev_info(adev->dev, "%s: range.start = 0x%llx ranges.end = 0x%llx\n",
> +                       __func__, pgmap->range.start, pgmap->range.end);
> 
>         pgmap->nr_range = 1;
>         pgmap->ops = &svm_migrate_pgmap_ops;
> 
> 
> and get this in the case without nokaslr:
> 
> [    T367] amdgpu 0000:03:00.0: kfd_migrate: kgd2kfd_init_zone_device:
> range.start = 0xafe00000000 ranges.end = 0xaffffffffff
> 
> and this in the case with nokaslr:
> 
> [    T365] amdgpu 0000:03:00.0: kfd_migrate: kgd2kfd_init_zone_device:
> range.start = 0x3ffe00000000 ranges.end = 0x3fffffffffff
> 

So we should ignore the second region then for the purposes of this issue.

I think this now boils down to

Why is the dma_get_required_mask set to all of addressable memory (46 bits)
when we have nokaslr

Can you add some debug around that.

Thanks
Balbir