On Wed, Nov 04, 2020 at 04:37:58PM +0000, Christoph Hellwig wrote: > 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. Except that we don't really support pte-level gup-fast without CONFIG_ARCH_HAS_PTE_SPECIAL, and in fact all architectures selecting HAVE_FAST_GUP also select ARCH_HAS_PTE_SPECIAL, so we should be fine.
