[PATCH v2] drm/ttm: Do not put non-struct page memory into PUD/PMDs

[Jason Gunthorpe]

On Wed, Oct 20, 2021 at 08:34:33AM +0200, Thomas Hellström wrote:

> Follow up question: If we resurrect this in the proper way (and in that case
> only for x86_64) is there something we need to pay particular attention to
> WRT the ZONE_DEVICE refcounting fixing you mention above?

Similar to PTE it should be completely separated from ZONE_DEVICE.

Seeing the special bit set at any level should trigger all page table
walkers to never try to get a struct page.

Today some of the page table walkers are trying to do this with
vma_is_special(), all of those should end up being the Pxx_SPECIAL
test instead.

Jason