linux-kernel - [PATCH 3.16.y-ckt 128/185] arm64: Don't report clear pmds and puds as huge

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Date:	Wed, 15 Jul 2015 10:12:03 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Christoffer Dall <christoffer.dall@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 128/185] arm64: Don't report clear pmds and puds as huge

3.16.7-ckt15 -stable review patch.  If anyone has any objections, please let me know.

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

From: Christoffer Dall <christoffer.dall@...aro.org>

commit fd28f5d439fca77348c129d5b73043a56f8a0296 upstream.

The current pmd_huge() and pud_huge() functions simply check if the table
bit is not set and reports the entries as huge in that case.  This is
counter-intuitive as a clear pmd/pud cannot also be a huge pmd/pud, and
it is inconsistent with at least arm and x86.

To prevent others from making the same mistake as me in looking at code
that calls these functions and to fix an issue with KVM on arm64 that
causes memory corruption due to incorrect page reference counting
resulting from this mistake, let's change the behavior.

Signed-off-by: Christoffer Dall <christoffer.dall@...aro.org>
Reviewed-by: Steve Capper <steve.capper@...aro.org>
Acked-by: Marc Zyngier <marc.zyngier@....com>
Fixes: 084bd29810a5 ("ARM64: mm: HugeTLB support.")
Signed-off-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 arch/arm64/mm/hugetlbpage.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index 023747bf4dd7..e3a24b75e53c 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -46,13 +46,13 @@ struct page *follow_huge_addr(struct mm_struct *mm, unsigned long address,
 
 int pmd_huge(pmd_t pmd)
 {
-	return !(pmd_val(pmd) & PMD_TABLE_BIT);
+	return pmd_val(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT);
 }
 
 int pud_huge(pud_t pud)
 {
 #ifndef __PAGETABLE_PMD_FOLDED
-	return !(pud_val(pud) & PUD_TABLE_BIT);
+	return pud_val(pud) && !(pud_val(pud) & PUD_TABLE_BIT);
 #else
 	return 0;
 #endif
--
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