[PATCH] drm/ttm: Temporarily disable the huge_fault() callback

Thomas Hellström (VMware) thomas_os at shipmail.org
Wed Apr 8 13:49:54 UTC 2020


On 4/8/20 2:19 PM, Christian König wrote:
> Am 08.04.20 um 14:01 schrieb Thomas Hellström (VMware):
>> Hi, Christian,
>>
>> On 4/8/20 1:53 PM, Thomas Hellström (VMware) wrote:
>>> From: "Thomas Hellstrom (VMware)" <thomas_os at shipmail.org>
>>>
>>> With amdgpu and CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y, there are
>>> errors like:
>>> BUG: non-zero pgtables_bytes on freeing mm
>>> and:
>>> BUG: Bad rss-counter state
>>> with TTM transparent huge-pages.
>>> Until we've figured out what other TTM drivers do differently 
>>> compared to
>>> vmwgfx, disable the huge_fault() callback, eliminating transhuge
>>> page-table entries.
>>>
>>> Cc: Christian König <christian.koenig at amd.com>
>>> Signed-off-by: Thomas Hellstrom (VMware) <thomas_os at shipmail.org>
>>> Reported-by: Alex Xu (Hello71) <alex_y_xu at yahoo.ca>
>>> Tested-by: Alex Xu (Hello71) <alex_y_xu at yahoo.ca>
>
> Acked-by: Christian König <christian.koenig at amd.com>
>
>>> ---
>>
>> Without being able to test and track this down on amdgpu there's 
>> little more than this I can do at the moment. Hopefully I'll be able 
>> to test on nouveau/ttm after getting back from vacation to see if I 
>> can reproduce.
>>
>> It looks like some part of the kernel mistakes a huge page-table 
>> entry for a page directory, and that would be a path that is not hit 
>> with vmwgfx.
>
> Well that looks like an ugly one and I don't know enough about the 
> page table handling to hunt this down either.
>
> BTW: Have you seen the coverity warning about  "WARN_ON_ONCE(ret = 
> VM_FAULT_FALLBACK);"?

Yes, that's a false warning but it might be that it should be rewritten 
for clarity like so:

ret = VM_FAULT_FALLBACK;
WARN_ON_ONCE(true);

/Thomas



>
> Regards,
> Christian.
>
>>
>> /Thomas
>>
>>



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