From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH] of, numa: Validate some distance map rules Date: Wed, 7 Nov 2018 15:44:31 +0000 Message-ID: <20181107154430.GA9996@brain-police> References: <1541507973-149965-1-git-send-email-john.garry@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1541507973-149965-1-git-send-email-john.garry@huawei.com> Sender: linux-kernel-owner@vger.kernel.org To: John Garry Cc: robh+dt@kernel.org, frowand.list@gmail.com, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linuxarm@huawei.com, anshuman.khandual@arm.com, peterz@infradead.org List-Id: devicetree@vger.kernel.org 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 Is it worth mentioning that the lack of this check was leading to a kernel crash with a malformed DT entry? > 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