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

wildea01 · ctmarinas · commit 4e6020565596 · 2018-02-06T22:53:16.000Z
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 &lt;will.deacon@arm.com&gt;
Signed-off-by: Catalin Marinas &lt;catalin.marinas@arm.com&gt;
diff --git 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;
 }
 

Original file line number	Diff line number	Diff line change
`@@ -118,6 +118,10 @@ static bool pgattr_change_is_safe(u64 old, u64 new)`
`118`	`118`	`if ((old \| new) & PTE_CONT)`
`119`	`119`	`return false;`
`120`	`120`
	`121`	`+ /* Transitioning from Global to Non-Global is safe */`
	`122`	`+ if (((old ^ new) == PTE_NG) && (new & PTE_NG))`
	`123`	`+ return true;`
	`124`	`+`
`121`	`125`	`return ((old ^ new) & ~mask) == 0;`
`122`	`126`	`}`
`123`	`127`