arm64: mm: Permit transitioning from Global to Non-Global without BBM

BugLink: http://bugs.launchpad.net/bugs/1751064
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>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 916d9ced1c3f99003e59626c05283d9a433c2997..451f96f3377ca5dc584e399f545725baf69c4858 100644 (file)
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -117,6 +117,10 @@ static bool pgattr_change_is_safe(u64 old, u64 new)
        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;
 }