[PATCH 3.8 087/166] mm: numa: do not clear PTE for pte_numa update

[Kamal Mostafa]

3.8.13.16 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mel Gorman <mgorman at suse.de>

commit 0c5f83c23ca703d32f930393825487257a5cde6d upstream.

The TLB must be flushed if the PTE is updated but change_pte_range is
clearing the PTE while marking PTEs pte_numa without necessarily
flushing the TLB if it reinserts the same entry.  Without the flush,
it's conceivable that two processors have different TLBs for the same
virtual address and at the very least it would generate spurious faults.

This patch only unmaps the pages in change_pte_range for a full
protection change.

[riel at redhat.com: write pte_numa pte back to the page tables]
Signed-off-by: Mel Gorman <mgorman at suse.de>
Signed-off-by: Rik van Riel <riel at redhat.com>
Reviewed-by: Rik van Riel <riel at redhat.com>
Cc: Alex Thorlton <athorlton at sgi.com>
Cc: Chegu Vinod <chegu_vinod at hp.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 mm/mprotect.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 4c35eb8..79abf13 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -54,13 +54,14 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 			pte_t ptent;
 			bool updated = false;
 
-			ptent = ptep_modify_prot_start(mm, addr, pte);
 			if (!prot_numa) {
+				ptent = ptep_modify_prot_start(mm, addr, pte);
 				ptent = pte_modify(ptent, newprot);
 				updated = true;
 			} else {
 				struct page *page;
 
+				ptent = *pte;
 				page = vm_normal_page(vma, addr, oldpte);
 				if (page) {
 					int this_nid = page_to_nid(page);
@@ -73,6 +74,7 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 					if (!pte_numa(oldpte) &&
 					    page_mapcount(page) == 1) {
 						ptent = pte_mknuma(ptent);
+						set_pte_at(mm, addr, pte, ptent);
 						updated = true;
 					}
 				}
@@ -89,7 +91,10 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 
 			if (updated)
 				pages++;
-			ptep_modify_prot_commit(mm, addr, pte, ptent);
+
+			/* Only !prot_numa always clears the pte */
+			if (!prot_numa)
+				ptep_modify_prot_commit(mm, addr, pte, ptent);
 		} else if (IS_ENABLED(CONFIG_MIGRATION) && !pte_file(oldpte)) {
 			swp_entry_t entry = pte_to_swp_entry(oldpte);
 
-- 
1.8.3.2