[Intel-gfx] [PATCH 4/4] i915: fix remap_io_sg to verify the pgprot

[Christoph Hellwig]

On Tue, May 18, 2021 at 08:46:44AM +0200, Thomas Hellström wrote:
> And worse, if we prefault a user-space buffer object map using 
> remap_io_sg() and then zap some ptes using madvise(), the next time those 
> ptes are accessed, we'd trigger a new call to remap_io_sg() which would now 
> find already populated ptes. While the old code looks to just silently 
> overwrite those, it looks like the new code would BUG in remap_pte_range()?

How can you zap the PTEs using madvise?