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

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>

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index b44992e..fc7902b 100644 (file)
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -118,6 +118,10 @@ 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;
 }