mm, dax: dax-pmd vs thp-pmd vs hugetlbfs-pmd

A dax-huge-page mapping while it uses some thp helpers is ultimately not
a transparent huge page.  The distinction is especially important in the
get_user_pages() path.  pmd_devmap() is used to distinguish dax-pmds
from pmd_huge() and pmd_trans_huge() which have slightly different
semantics.

Explicitly mark the pmd_trans_huge() helpers that dax needs by adding
pmd_devmap() checks.

[kirill.shutemov@linux.intel.com: fix regression in handling mlocked pages in  __split_huge_pmd()]
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 6047707085c1..8eb7bb40dc40 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -149,7 +149,8 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
                 unsigned long this_pages;
 
                 next = pmd_addr_end(addr, end);
-                if (!pmd_trans_huge(*pmd) && pmd_none_or_clear_bad(pmd))
+                if (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd)
+                                && pmd_none_or_clear_bad(pmd))
                         continue;
 
                 /* invoke the mmu notifier if the pmd is populated */
@@ -158,7 +159,7 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
                         mmu_notifier_invalidate_range_start(mm, mni_start, end);
                 }
 
-                if (pmd_trans_huge(*pmd)) {
+                if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
                         if (next - addr != HPAGE_PMD_SIZE)
                                 split_huge_pmd(vma, pmd, addr);
                         else {