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    Subject[PATCH 4.15 043/202] [Variant 3/Meltdown] arm64: mm: Permit transitioning from Global to Non-Global without BBM
    Date
    4.15-stable review patch.  If anyone has any objections, please let me know.

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

    From: Will Deacon <will.deacon@arm.com>


    Commit 4e6020565596 upstream.

    Break-before-make is not needed when transitioning from Global to
    Non-Global mappings, provided that the contiguous hint is not being used.

    Signed-off-by: Will Deacon <will.deacon@arm.com>
    Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/arm64/mm/mmu.c | 4 ++++
    1 file changed, 4 insertions(+)

    --- a/arch/arm64/mm/mmu.c
    +++ b/arch/arm64/mm/mmu.c
    @@ -117,6 +117,10 @@ static bool pgattr_change_is_safe(u64 ol
    if ((old | new) & PTE_CONT)
    return false;

    + /* Transitioning from Global to Non-Global is safe */
    + if (((old ^ new) == PTE_NG) && (new & PTE_NG))
    + return true;
    +
    return ((old ^ new) & ~mask) == 0;
    }


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