From: Will Deacon <will.deacon@arm.com>
Date: Mon, 29 Jan 2018 11:59:54 +0000 (+0000)
Subject: arm64: mm: Permit transitioning from Global to Non-Global without BBM
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=4e602056559633303d7e5bb2ff624778ca248f68;p=linux.git

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 b44992ec9643e..fc7902bda02bc 100644
--- 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;
 }