mm: numa: do not trap faults on the huge zero page

Faults on the huge zero page are pointless and there is a BUG_ON to catch
them during fault time.  This patch reintroduces a check that avoids
marking the zero page PAGE_NONE.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Dave Jones <davej@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Kirill Shutemov <kirill.shutemov@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 1 deletions

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 76824d73380d..dd599fc235c2 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -76,6 +76,18 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
                 if (pte_present(oldpte)) {
                         pte_t ptent;
 
+                        /*
+                         * Avoid trapping faults against the zero or KSM
+                         * pages. See similar comment in change_huge_pmd.
+                         */
+                        if (prot_numa) {
+                                struct page *page;
+
+                                page = vm_normal_page(vma, addr, oldpte);
+                                if (!page || PageKsm(page))
+                                        continue;
+                        }
+
                         ptent = ptep_modify_prot_start(mm, addr, pte);
                         ptent = pte_modify(ptent, newprot);
 
@@ -142,7 +154,7 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
                                 split_huge_page_pmd(vma, addr, pmd);
                         else {
                                 int nr_ptes = change_huge_pmd(vma, pmd, addr,
-                                                newprot);
+                                                newprot, prot_numa);
 
                                 if (nr_ptes) {
                                         if (nr_ptes == HPAGE_PMD_NR) {