[PATCH 4.14 051/195] [Variant 3/Meltdown] arm64: mm: Permit transitioning from Global to Non-Global without BBM

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

--

From: Will Deacon 


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 
Signed-off-by: Catalin Marinas 
Signed-off-by: Ard Biesheuvel 
Signed-off-by: Greg Kroah-Hartman 
---
 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;
 }
 

[PATCH 4.14 051/195] [Variant 3/Meltdown] arm64: mm: Permit transitioning from Global to Non-Global without BBM

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

--

From: Will Deacon 


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 
Signed-off-by: Catalin Marinas 
Signed-off-by: Ard Biesheuvel 
Signed-off-by: Greg Kroah-Hartman 
---
 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;
 }