linux-kernel - [PATCH 3.16 182/305] ARM: 8579/1: mm: Fix definition of pmd

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Date:	Sat, 13 Aug 2016 18:42:51 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Will Deacon" <will.deacon@....com>,
	"Russell King" <rmk+kernel@....linux.org.uk>,
	"Steve Capper" <steve.capper@....com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	"Russell King" <linux@...linux.org.uk>,
	"Catalin Marinas" <catalin.marinas@....com>
Subject: [PATCH 3.16 182/305] ARM: 8579/1: mm: Fix definition of
 pmd_mknotpresent

3.16.37-rc1 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>
[bwh: Backported to 3.16: also convert from a macro to a function, as done
 earlier upstream]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/arch/arm/include/asm/pgtable-3level.h
+++ b/arch/arm/include/asm/pgtable-3level.h
@@ -243,8 +243,11 @@ 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 */
-#define pmd_mknotpresent(pmd)	(__pmd(0))
+/* represent a notpresent pmd by faulting entry, this is used by pmdp_invalidate */
+static inline pmd_t pmd_mknotpresent(pmd_t pmd)
+{
+	return __pmd(pmd_val(pmd) & ~L_PMD_SECT_VALID);
+}
 
 static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
 {