linux-kernel - [PATCH 19/18] mm,numa: write pte_numa pte back to the page tables

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Date:	Mon, 16 Dec 2013 18:15:13 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Alex Thorlton <athorlton@....com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>, chegu_vinod@...com
Subject: [PATCH 19/18] mm,numa: write pte_numa pte back to the page tables

On Tue, 10 Dec 2013 15:51:23 +0000
Mel Gorman <mgorman@...e.de> wrote:

> 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.

Turns out the patch optimized out not one, but both
pte writes. Oops.

We'll need this one too, Andrew :)

---8<---

Subject: mm,numa: write pte_numa pte back to the page tables

The patch "mm: numa: Do not clear PTE for pte_numa update" cleverly
optimizes out an extraneous PTE write when changing the protection
of pages to pte_numa.

It also optimizes out actually writing the new pte_numa entry back
to the page tables. Oops.

Signed-off-by: Rik van Riel <riel@...hat.com>
Reported-by: Chegu Vinod <chegu_vinod@...com>
---
 mm/mprotect.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/mprotect.c b/mm/mprotect.c
index edc4e22..4114acf 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -67,6 +67,7 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 				if (page && !PageKsm(page)) {
 					if (!pte_numa(oldpte)) {
 						ptent = pte_mknuma(ptent);
+						set_pte_at(mm, addr, pte, ptent);
 						updated = true;
 					}
 				}
--
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