[PATCH 08/15] mm: numa: Do not clear PTE for pte_numa update

[Mel Gorman]

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.

Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
 mm/mprotect.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 18f1117..c53e332 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -52,13 +52,14 @@ 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) {
 					/* only check non-shared pages */
@@ -81,7 +82,10 @@ 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);
 
-- 
1.8.4

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