This is a note to let you know that I've just added the patch titled
drivers: base: cacheinfo: Fix shared_cpu_map changes in event of CPU hotplug
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
drivers-base-cacheinfo-fix-shared_cpu_map-changes-in.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 8bae8a477742df0e3c2501358796e6c1f3f94976
Author: K Prateek Nayak <kprateek.nayak@xxxxxxx>
Date: Mon May 8 14:11:14 2023 +0530
drivers: base: cacheinfo: Fix shared_cpu_map changes in event of CPU hotplug
[ Upstream commit 126310c9f669c9a8c875a3e5c2292299ca90225d ]
While building the shared_cpu_map, check if the cache level and cache
type matches. On certain systems that build the cache topology based on
the instance ID, there are cases where the same ID may repeat across
multiple cache levels, leading inaccurate topology.
In event of CPU offlining, the cache_shared_cpu_map_remove() does not
consider if IDs at same level are being compared. As a result, when same
IDs repeat across different cache levels, the CPU going offline is not
removed from all the shared_cpu_map.
Below is the output of cache topology of CPU8 and it's SMT sibling after
CPU8 is offlined on a dual socket 3rd Generation AMD EPYC processor
(2 x 64C/128T) running kernel release v6.3:
# for i in /sys/devices/system/cpu/cpu8/cache/index*/shared_cpu_list; do echo -n "$i: "; cat $i; done
/sys/devices/system/cpu/cpu8/cache/index0/shared_cpu_list: 8,136
/sys/devices/system/cpu/cpu8/cache/index1/shared_cpu_list: 8,136
/sys/devices/system/cpu/cpu8/cache/index2/shared_cpu_list: 8,136
/sys/devices/system/cpu/cpu8/cache/index3/shared_cpu_list: 8-15,136-143
# echo 0 > /sys/devices/system/cpu/cpu8/online
# for i in /sys/devices/system/cpu/cpu136/cache/index*/shared_cpu_list; do echo -n "$i: "; cat $i; done
/sys/devices/system/cpu/cpu136/cache/index0/shared_cpu_list: 136
/sys/devices/system/cpu/cpu136/cache/index1/shared_cpu_list: 8,136
/sys/devices/system/cpu/cpu136/cache/index2/shared_cpu_list: 8,136
/sys/devices/system/cpu/cpu136/cache/index3/shared_cpu_list: 9-15,136-143
CPU8 is removed from index0 (L1i) but remains in the shared_cpu_list of
index1 (L1d) and index2 (L2). Since L1i, L1d, and L2 are shared by the
SMT siblings, and they have the same cache instance ID, CPU 2 is only
removed from the first index with matching ID which is index1 (L1i) in
this case. With this fix, the results are as expected when performing
the same experiment on the same system:
# for i in /sys/devices/system/cpu/cpu8/cache/index*/shared_cpu_list; do echo -n "$i: "; cat $i; done
/sys/devices/system/cpu/cpu8/cache/index0/shared_cpu_list: 8,136
/sys/devices/system/cpu/cpu8/cache/index1/shared_cpu_list: 8,136
/sys/devices/system/cpu/cpu8/cache/index2/shared_cpu_list: 8,136
/sys/devices/system/cpu/cpu8/cache/index3/shared_cpu_list: 8-15,136-143
# echo 0 > /sys/devices/system/cpu/cpu8/online
# for i in /sys/devices/system/cpu/cpu136/cache/index*/shared_cpu_list; do echo -n "$i: "; cat $i; done
/sys/devices/system/cpu/cpu136/cache/index0/shared_cpu_list: 136
/sys/devices/system/cpu/cpu136/cache/index1/shared_cpu_list: 136
/sys/devices/system/cpu/cpu136/cache/index2/shared_cpu_list: 136
/sys/devices/system/cpu/cpu136/cache/index3/shared_cpu_list: 9-15,136-143
When rebuilding topology, the same problem appears as
cache_shared_cpu_map_setup() implements a similar logic. Consider the
same 3rd Generation EPYC processor: CPUs in Core 1, that share the L1
and L2 caches, have L1 and L2 instance ID as 1. For all the CPUs on
the second chiplet, the L3 ID is also 1 leading to grouping on CPUs from
Core 1 (1, 17) and the entire second chiplet (8-15, 24-31) as CPUs
sharing one cache domain. This went undetected since x86 processors
depended on arch specific populate_cache_leaves() method to repopulate
the shared_cpus_map when CPU came back online until kernel release
v6.3-rc5.
Fixes: 198102c9103f ("cacheinfo: Fix shared_cpu_map to handle shared caches at different levels")
Signed-off-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
Reviewed-by: Sudeep Holla <sudeep.holla@xxxxxxx>
Link: https://lore.kernel.org/r/20230508084115.1157-2-kprateek.nayak@xxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
index c440d1af197a4..26e13887aba46 100644
--- a/drivers/base/cacheinfo.c
+++ b/drivers/base/cacheinfo.c
@@ -280,6 +280,16 @@ static int cache_shared_cpu_map_setup(unsigned int cpu)
continue;/* skip if itself or no cacheinfo */
for (sib_index = 0; sib_index < cache_leaves(i); sib_index++) {
sib_leaf = per_cpu_cacheinfo_idx(i, sib_index);
+
+ /*
+ * Comparing cache IDs only makes sense if the leaves
+ * belong to the same cache level of same type. Skip
+ * the check if level and type do not match.
+ */
+ if (sib_leaf->level != this_leaf->level ||
+ sib_leaf->type != this_leaf->type)
+ continue;
+
if (cache_leaves_are_shared(this_leaf, sib_leaf)) {
cpumask_set_cpu(cpu, &sib_leaf->shared_cpu_map);
cpumask_set_cpu(i, &this_leaf->shared_cpu_map);
@@ -311,6 +321,16 @@ static void cache_shared_cpu_map_remove(unsigned int cpu)
for (sib_index = 0; sib_index < cache_leaves(sibling); sib_index++) {
sib_leaf = per_cpu_cacheinfo_idx(sibling, sib_index);
+
+ /*
+ * Comparing cache IDs only makes sense if the leaves
+ * belong to the same cache level of same type. Skip
+ * the check if level and type do not match.
+ */
+ if (sib_leaf->level != this_leaf->level ||
+ sib_leaf->type != this_leaf->type)
+ continue;
+
if (cache_leaves_are_shared(this_leaf, sib_leaf)) {
cpumask_clear_cpu(cpu, &sib_leaf->shared_cpu_map);
cpumask_clear_cpu(sibling, &this_leaf->shared_cpu_map);
