mm/gup: fix hugepd handling in hugetlb rework

Commit a12083d721d7 added hugepd handling for gup-slow, reusing gup-fast
functions.  follow_hugepd() correctly took the vma pointer in, however
didn't pass it over into the lower functions, which was overlooked.

The issue is gup_fast_hugepte() uses the vma pointer to make the correct
decision on whether an unshare is needed for a FOLL_PIN|FOLL_LONGTERM. 
Now without vma ponter it will constantly return "true" (needs an unshare)
for a page cache, even though in the SHARED case it will be wrong to
unshare.

The other problem is, even if an unshare is needed, it now returns 0
rather than -EMLINK, which will not trigger a follow up FAULT_FLAG_UNSHARE
fault.  That will need to be fixed too when the unshare is wanted.

gup_longterm test didn't expose this issue in the past because it didn't
yet test R/O unshare in this case, another separate patch will enable that
in future tests.

Fix it by passing vma correctly to the bottom, rename gup_fast_hugepte()
back to gup_hugepte() as it is shared between the fast/slow paths, and
also allow -EMLINK to be returned properly by gup_hugepte() even though
gup-fast will take it the same as zero.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: a12083d721d7 ("mm/gup: handle hugepd for follow_page()")
Signed-off-by: Peter Xu <[email protected]>
Reported-by: David Hildenbrand <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Cc: Aneesh Kumar K.V <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Muchun Song <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions