Re: [PATCH] arm64/numa: Add more vetting in numa_set_distance()

[Will Deacon]

On Mon, Oct 29, 2018 at 12:14:09PM +0000, John Garry wrote:
> On 29/10/2018 11:25, Will Deacon wrote:
> >On Fri, Oct 26, 2018 at 09:57:47PM +0800, John Garry wrote:
> >>Currently it is acceptable to set the distance between 2 separate nodes to
> >>LOCAL_DISTANCE.
> >>
> >>Reject this as it is invalid.
> >>
> >>This change avoids a crash reported in [1].
> >>
> >>[1] https://www.spinics.net/lists/arm-kernel/msg683304.html
> >>
> >>Signed-off-by: John Garry <john.garry@xxxxxxxxxx>
> >>
> >>diff --git a/arch/arm64/mm/numa.c b/arch/arm64/mm/numa.c
> >>index 146c04c..6092e3d 100644
> >>--- a/arch/arm64/mm/numa.c
> >>+++ b/arch/arm64/mm/numa.c
> >>@@ -335,7 +335,8 @@ void __init numa_set_distance(int from, int to, int distance)
> >> 	}
> >>
> >> 	if ((u8)distance != distance ||
> >>-	    (from == to && distance != LOCAL_DISTANCE)) {
> >>+	    (from == to && distance != LOCAL_DISTANCE) ||
> >>+	    (from != to && distance == LOCAL_DISTANCE)) {
> >
> >The current code here is more-or-less lifted from the x86 implementation
> >of numa_set_distance().
> 
> Right, I did notice this. I didn't think that x86 folks would be so
> concerned since they generally only use ACPI, and the ACPI code already
> validates these distances in drivers/acpi/numa.c: slit_valid() [unlike OF
> code].
> 
>  I think we should either factor out the sanity check
> >into a core helper or make the core code robust to these funny configurations.
> 
> OK, so to me it would make sense to factor out a sanity check into a core
> helper.

That, or have the OF code perform the same validation that slit_valid() is
doing for ACPI. I'm just trying to avoid other architectures running into
this problem down the line.

Will