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

[John Garry]

On 29/10/2018 11:25, Will Deacon wrote:
> Hi John,

Hi Will,

> 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.

Cheers,
John

> Will
>
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