4.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Steve Capper <steve.capper@xxxxxxx>
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@xxxxxxx: 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@xxxxxxxxxxxxxxx>
Acked-by: Will Deacon <will.deacon@xxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxx>
Signed-off-by: Steve Capper <steve.capper@xxxxxxx>
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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)
--
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