linux-kernel - [PATCH 4.16 070/272] mm: thp: fix potential clearing to referenced flag in page_idle_clear_pte_refs

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Message-Id: <20180528100246.789221954@linuxfoundation.org>
Date:   Mon, 28 May 2018 12:01:43 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Yang Shi <yang.shi@...ux.alibaba.com>,
        Gang Deng <gavin.dg@...ux.alibaba.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.16 070/272] mm: thp: fix potential clearing to referenced flag in page_idle_clear_pte_refs_one()

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

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

From: Yang Shi <yang.shi@...ux.alibaba.com>

[ Upstream commit f0849ac0b8e072073ec5fcc7fadd05a77434364e ]

For PTE-mapped THP, the compound THP has not been split to normal 4K
pages yet, the whole THP is considered referenced if any one of sub page
is referenced.

When walking PTE-mapped THP by pvmw, all relevant PTEs will be checked
to retrieve referenced bit.  But, the current code just returns the
result of the last PTE.  If the last PTE has not referenced, the
referenced flag will be cleared.

Just set referenced when ptep{pmdp}_clear_young_notify() returns true.

Link: http://lkml.kernel.org/r/1518212451-87134-1-git-send-email-yang.shi@linux.alibaba.com
Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
Reported-by: Gang Deng <gavin.dg@...ux.alibaba.com>
Suggested-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Reviewed-by: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 mm/page_idle.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

--- a/mm/page_idle.c
+++ b/mm/page_idle.c
@@ -65,11 +65,15 @@ static bool page_idle_clear_pte_refs_one
 	while (page_vma_mapped_walk(&pvmw)) {
 		addr = pvmw.address;
 		if (pvmw.pte) {
-			referenced = ptep_clear_young_notify(vma, addr,
-					pvmw.pte);
+			/*
+			 * For PTE-mapped THP, one sub page is referenced,
+			 * the whole THP is referenced.
+			 */
+			if (ptep_clear_young_notify(vma, addr, pvmw.pte))
+				referenced = true;
 		} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
-			referenced = pmdp_clear_young_notify(vma, addr,
-					pvmw.pmd);
+			if (pmdp_clear_young_notify(vma, addr, pvmw.pmd))
+				referenced = true;
 		} else {
 			/* unexpected pmd-mapped page? */
 			WARN_ON_ONCE(1);