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

[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>
> ---

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.

/Thomas