From: Steve Capper <redacted>

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 at arm.com: using L_PMD_SECT_VALID instead of PMD_TYPE_SECT]

Fixes: 8d9625070073 ("ARM: mm: Transparent huge page support for LPAE systems.")
Cc: <redacted> # 3.11+: 624531886987: ARM: 8578/1: mm: ensure pmd_present only checks the valid bit
Reported-by: Kirill A. Shutemov <redacted>
Acked-by: Will Deacon <redacted>
Cc: Russell King <linux@armlinux.org.uk>
Signed-off-by: Steve Capper <redacted>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <redacted>
---

This is a backport of commit 56530f5d2ddc ("ARM: 8579/1: mm: Fix 
definition of pmd_mknotpresent") to the 3.14.x  stable kernel and
earlier because the original patch does not apply cleanly.

As noted in the "Cc: stable" tag above, this patch requires commit 
624531886987 ("ARM: 8578/1: mm: ensure pmd_present only checks the valid
bit"), already queued for 3.14.x stable kernel.

 arch/arm/include/asm/pgtable-3level.h | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/arm/include/asm/pgtable-3level.h b/arch/arm/include/asm/pgtable-3level.h
index ab7ee9205ca4..40d60a679fc8 100644
--- 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)
 {