thp: mprotect: transparent huge page support

Natively handle huge pmds when changing page tables on behalf of
mprotect().

I left out update_mmu_cache() because we do not need it on x86 anyway but
more importantly the interface works on ptes, not pmds.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 9402080d0d4..5a688a2756b 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -88,7 +88,13 @@ static inline void change_pmd_range(struct vm_area_struct *vma, pud_t *pud,
         pmd = pmd_offset(pud, addr);
         do {
                 next = pmd_addr_end(addr, end);
-                split_huge_page_pmd(vma->vm_mm, pmd);
+                if (pmd_trans_huge(*pmd)) {
+                        if (next - addr != HPAGE_PMD_SIZE)
+                                split_huge_page_pmd(vma->vm_mm, pmd);
+                        else if (change_huge_pmd(vma, pmd, addr, newprot))
+                                continue;
+                        /* fall through */
+                }
                 if (pmd_none_or_clear_bad(pmd))
                         continue;
                 change_pte_range(vma->vm_mm, pmd, addr, next, newprot,