Re: [PATCH v5 05/15] mm/frame-vector: Use FOLL_LONGTERM

[Christoph Hellwig]

On Wed, Nov 04, 2020 at 05:26:58PM +0100, Daniel Vetter wrote:
> What we're discussing is whether gup_fast and pup_fast also obey this,
> or fall over and can give you the struct page that's backing the
> dma_mmap_* memory. Since the _fast variant doesn't check for
> vma->vm_flags, and afaict that's the only thing which closes this gap.
> And like you restate, that would be a bit a problem. So where's that
> check which Jason&me aren't spotting?

remap_pte_range uses pte_mkspecial to set up the PTEs, and gup_pte_range
errors out on pte_special.  Of course this only works for the
CONFIG_ARCH_HAS_PTE_SPECIAL case, for other architectures we do have
a real problem.