Re: commit 7ffb791423c7 breaks steam game

[Balbir Singh <balbirs@nvidia.com>]

On 3/26/25 10:43, Balbir Singh wrote:
> 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
> 

I think I know the root cause of the required_mask going up and hence the
use of DMA32

1. HMM calls add_pages()
2. add_pages calls update_end_of_memory_vars()
3. This updates max_pfn and that causes required_mask to go up to 46 bits

Do you have CONFIG_HSA_AMD_SVM enabled? Does turning it off, fix the issue?

The actual issue is the update of max_pfn.

Balbir Singh