[PATCH 2/7] check hugepage swap entry in get_user_pages_fast()

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

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@ah.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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