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    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@arm.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@arm.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@linux.intel.com>
    Acked-by: Will Deacon <will.deacon@arm.com>
    Cc: Russell King <linux@armlinux.org.uk>
    Signed-off-by: Steve Capper <steve.capper@arm.com>
    Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
    Signed-off-by: Russell King <rmk+kernel@arm.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@decadent.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)
    {
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