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

[Christian König]

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);"?

Regards,
Christian.

>
> /Thomas
>
>