Messages in this thread | | | Subject | Re: [PATCH] of, numa: Validate some distance map rules | From | John Garry <> | Date | Wed, 7 Nov 2018 16:24:45 +0000 |
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On 07/11/2018 15:55, Rob Herring wrote: > On Wed, Nov 07, 2018 at 03:44:31PM +0000, Will Deacon wrote: >> Hi John, >> >> On Tue, Nov 06, 2018 at 08:39:33PM +0800, John Garry wrote: >>> Currently the NUMA distance map parsing does not validate the distance >>> table for the distance-matrix rules 1-2 in [1]. >>> >>> However the arch NUMA code may enforce some of these rules, but not all. >>> Such is the case for the arm64 port, which does not enforce the rule that >>> the distance between separates nodes cannot equal LOCAL_DISTANCE. >>> >>> The patch adds the following rules validation: >>> - distance of node to self equals LOCAL_DISTANCE >>> - distance of separate nodes > LOCAL_DISTANCE >>> >>> A note on dealing with symmetrical distances between nodes: >>> >>> Validating symmetrical distances between nodes is difficult. If it were >>> mandated in the bindings that every distance must be recorded in the >>> table, validating symmetrical distances would be straightforward. However, >>> it isn't. >>> >>> In addition to this, it is also possible to record [b, a] distance only >>> (and not [a, b]). So, when processing the table for [b, a], we cannot >>> assert that current distance of [a, b] != [b, a] as invalid, as [a, b] >>> distance may not be present in the table and current distance would be >>> default at REMOTE_DISTANCE. >>> >>> As such, we maintain the policy that we overwrite distance [a, b] = [b, a] >>> for b > a. This policy is different to kernel ACPI SLIT validation, which >>> allows non-symmetrical distances (ACPI spec SLIT rules allow it). However, >>> the debug message is dropped as it may be misleading (for a distance which >>> is later overwritten). >>> >>> Some final notes on semantics: >>> >>> - It is implied that it is the responsibility of the arch NUMA code to >>> reset the NUMA distance map for an error in distance map parsing. >>> >>> - It is the responsibility of the FW NUMA topology parsing (whether OF or >>> ACPI) to enforce NUMA distance rules, and not arch NUMA code. >>> >>> [1] Documents/devicetree/bindings/numa.txt >>> >>> Signed-off-by: John Garry <john.garry@huawei.com> >> >> Is it worth mentioning that the lack of this check was leading to a kernel >> crash with a malformed DT entry?
Yeah, I was thinking in hindsight that I should have mentioned the yet-unresolved crash we avoid.
> > So should be marked for stable too?
Probably. So this patch is masking a crash I have observed, which may be good enough reason on its own.
In addition, I would still say that failing to validate the distance map falls into the "oh, that's not good" category of stable rules.
> >> >>> diff --git a/drivers/of/of_numa.c b/drivers/of/of_numa.c >>> index 35c64a4295e0..fe6b13608e51 100644 >>> --- a/drivers/of/of_numa.c >>> +++ b/drivers/of/of_numa.c >>> @@ -104,9 +104,14 @@ static int __init of_numa_parse_distance_map_v1(struct device_node *map) >>> distance = of_read_number(matrix, 1); >>> matrix++; >>> >>> + if ((nodea == nodeb && distance != LOCAL_DISTANCE) || >>> + (nodea != nodeb && distance <= LOCAL_DISTANCE)) { >>> + pr_err("Invalid distance[node%d -> node%d] = %d\n", >>> + nodea, nodeb, distance); >>> + return -EINVAL; >>> + } >>> + >>> numa_set_distance(nodea, nodeb, distance); >>> - pr_debug("distance[node%d -> node%d] = %d\n", >>> - nodea, nodeb, distance); >> >> Looks good to me, although I'm not sure which tree this should go through. >> >> Acked-by: Will Deacon <will.deacon@arm.com> >
Thanks Will.
> I'll take it. Please resend with the comment Will asked for. >
OK, I'll repost an updated version.
> Rob >
Cheers, john
> . >
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