linux-kernel - [PATCH 4.6 062/203] ARM: 8579/1: mm: Fix definition of pmd

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Message-Id: <20160725203431.810348178@linuxfoundation.org>
Date:	Mon, 25 Jul 2016 13:54:37 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Will Deacon <will.deacon@....com>,
	Russell King <linux@...linux.org.uk>,
	Steve Capper <steve.capper@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Russell King <rmk+kernel@....linux.org.uk>
Subject: [PATCH 4.6 062/203] ARM: 8579/1: mm: Fix definition of pmd_mknotpresent

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

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

From: Steve Capper <steve.capper@....com>

commit 56530f5d2ddc9b9fade7ef8db9cb886e9dc689b5 upstream.

Currently pmd_mknotpresent will use a zero entry to respresent an
invalidated pmd.

Unfortunately this definition clashes with pmd_none, thus it is
possible for a race condition to occur if zap_pmd_range sees pmd_none
whilst __split_huge_pmd_locked is running too with pmdp_invalidate
just called.

This patch fixes the race condition by modifying pmd_mknotpresent to
create non-zero faulting entries (as is done in other architectures),
removing the ambiguity with pmd_none.

[catalin.marinas@....com: using L_PMD_SECT_VALID instead of PMD_TYPE_SECT]

Fixes: 8d9625070073 ("ARM: mm: Transparent huge page support for LPAE systems.")
Reported-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Acked-by: Will Deacon <will.deacon@....com>
Cc: Russell King <linux@...linux.org.uk>
Signed-off-by: Steve Capper <steve.capper@....com>
Signed-off-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Russell King <rmk+kernel@....linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/arm/include/asm/pgtable-3level.h |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/arm/include/asm/pgtable-3level.h
+++ b/arch/arm/include/asm/pgtable-3level.h
@@ -250,10 +250,10 @@ PMD_BIT_FUNC(mkyoung,   |= PMD_SECT_AF);
 #define pfn_pmd(pfn,prot)	(__pmd(((phys_addr_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot)))
 #define mk_pmd(page,prot)	pfn_pmd(page_to_pfn(page),prot)

-/* represent a notpresent pmd by zero, this is used by pmdp_invalidate */
+/* represent a notpresent pmd by faulting entry, this is used by pmdp_invalidate */
 static inline pmd_t pmd_mknotpresent(pmd_t pmd)
 {
-	return __pmd(0);
+	return __pmd(pmd_val(pmd) & ~L_PMD_SECT_VALID);
 }

 static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)