linux-kernel - [PATCH 2/7] check hugepage swap entry in get_user_pages

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Message-Id: <1295591340-1862-3-git-send-email-n-horiguchi@ah.jp.nec.com>
Date:	Fri, 21 Jan 2011 15:28:55 +0900
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Andi Kleen <tatsu@...jp.nec.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Mel Gorman <mel@....ul.ie>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Huang Ying <ying.huang@...el.com>,
	Fernando Luis Vazquez Cao <fernando@....ntt.co.jp>,
	tony.luck@...el.com, LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: [PATCH 2/7] check hugepage swap entry in get_user_pages_fast()

When the hugepage associated with a given address is HWPOISONed
or under page migration, get_user_pages_fast() need to fall back
to slow path in order to make the page fault fail (when HWPOISONed)
or to wait for migration completion (when under migration.)

Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
---
 arch/x86/mm/gup.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git v2.6.38-rc1/arch/x86/mm/gup.c v2.6.38-rc1/arch/x86/mm/gup.c
index dbe34b9..93b74dd 100644
--- v2.6.38-rc1/arch/x86/mm/gup.c
+++ v2.6.38-rc1/arch/x86/mm/gup.c
@@ -176,6 +176,15 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
 		 */
 		if (pmd_none(pmd) || pmd_trans_splitting(pmd))
 			return 0;
+		/*
+		 * PMD can be in swap entry style when the hugepage
+		 * pointed to by it is hwpoisoned or under migration.
+		 * Because the swap entry format has no flag showing
+		 * the page size, pmd_large() cannot detect it.
+		 * So then we just fall back to the slow path.
+		 */
+		if (unlikely(!pmd_present(pmd)))
+			return 0;
 		if (unlikely(pmd_large(pmd))) {
 			if (!gup_huge_pmd(pmd, addr, next, write, pages, nr))
 				return 0;
-- 
1.7.3.4

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