Re: [PATCH 0/2] fix for direct-I/O to DAX mappings

[Xiong Zhou <xzhou@redhat.com>]

On Sat, Feb 25, 2017 at 09:08:28AM -0800, Dan Williams wrote:
> Hi Andrew,
> 
> While Ross was doing a review of a new mmap+DAX direct-I/O test case for
> xfstests, from Xiong, he noticed occasions where it failed to trigger a
> page dirty event.  Dave then spotted the problem fixed by patch1. The
> pte_devmap() check is precluding pte_allows_gup(), i.e. bypassing
> permission checks and dirty tracking.

This mmap-dax-dio case still fails with this patchset, while it makes
sense. It's the test case that need to be fixed.

BTW, this patchset fixes another xfsrestore issue, which i hit now
and then, xfs/301 w/ or wo/ DAX only on nvdimms. xfsrestore never
return but killable.

Thanks,
> 
> Patch2 is a cleanup and clarifies that pte_unmap() only needs to be done
> once per page-worth of ptes. It unifies the exit paths similar to the
> generic gup_pte_range() in the __HAVE_ARCH_PTE_SPECIAL case.
> 
> I'm sending this through the -mm tree for a double-check from memory
> management folks. It has a build success notification from the kbuild
> robot.
> 
> ---
> 
> Dan Williams (2):
>       x86, mm: fix gup_pte_range() vs DAX mappings
>       x86, mm: unify exit paths in gup_pte_range()
> 
> 
>  arch/x86/mm/gup.c |   37 +++++++++++++++++++++----------------
>  1 file changed, 21 insertions(+), 16 deletions(-)