[PATCH 0/2] drivers: base: cacheinfo: Fix shared_cpu_list inconsistency in event of CPU hotplug

[K Prateek Nayak <kprateek.nayak@amd.com>]

Since v6.3-rc1, the shared_cpu_list in per-cpu cacheinfo breaks in case
of hotplug activity on x86. This can be tracked back to two commits:

o commit 198102c9103f ("cacheinfo: Fix shared_cpu_map to handle shared
  caches at different levels") that matches cache instance IDs without
  considering if the instance IDs belong to same cache level or not.

o commit 5c2712387d48 ("cacheinfo: Fix LLC is not exported through
  sysfs") which skips calling populate_cache_leaves() if
  last_level_cache_is_valid(cpu) returns true. populate_cache_leaves()
  on x86 would have populated the shared_cpu_map when CPU comes online,
  which is now skipped, and the alternate path has an early bailout
  before setting the CPU in the shared_cpu_map is even attempted.

  On x86, populate_cache_leaves() also sets the
  cpu_cacheinfo->cpu_map_populated flag when the cacheinfo is first
  populated, the cache_shared_cpu_map_setup() in the driver is bypassed
  when a thread comes back online during the hotplug activity. This leads
  to the shared_cpu_list displaying abnormal values for the CPU that was
  offlined and then onlined since the shared_cpu_maps are never
  revaluated.

Following is the output from a dual socket 3rd Generation AMD EPYC
processor (2 x 64C/128T) for cachinfo when offlining and then onlining
CPU8:

o v6.3-rc5 with no changes:

  # 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
  # echo 1 > /sys/devices/system/cpu/cpu8/online

  # 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
    /sys/devices/system/cpu/cpu8/cache/index1/shared_cpu_list: 8
    /sys/devices/system/cpu/cpu8/cache/index2/shared_cpu_list: 8
    /sys/devices/system/cpu/cpu8/cache/index3/shared_cpu_list: 8

  # cat /sys/devices/system/cpu/cpu136/cache/index0/shared_cpu_list
    136

  # cat /sys/devices/system/cpu/cpu136/cache/index3/shared_cpu_list
    9-15,136-143

o v6.3-rc5 with commit 5c2712387d48 ("cacheinfo: Fix LLC is not exported
  through sysfs") reverted (Behavior consistent with v6.2):

  # 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
  # echo 1 > /sys/devices/system/cpu/cpu8/online

  # 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

  # cat /sys/devices/system/cpu/cpu136/cache/index0/shared_cpu_list
    8,136

  # cat /sys/devices/system/cpu/cpu136/cache/index3/shared_cpu_list
    8-15,136-143

This is not only limited to AMD processors but affects Intel processors
too. Following is the output from same experiment on a dual socket Intel
Ice Lake server (2 x 32C/64T) running kernel v6.3-rc5:

  # 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: 8,72
    /sys/devices/system/cpu/cpu8/cache/index1/shared_cpu_list: 8,72
    /sys/devices/system/cpu/cpu8/cache/index2/shared_cpu_list: 8,72
    /sys/devices/system/cpu/cpu8/cache/index3/shared_cpu_list: 0,2,4,6,8,10,12,14,16,18,20,22,24,
    26,28,30,32,34,36,38,40,42,44,46,48,50,52,54,56,58,60,62,64,66,68,70,72,74,76,78,80,82,84,86,
    88,90,92,94,96,98,100,102,104,106,108,110,112,114,116,118,120,122,124,126

  # echo 0 > /sys/devices/system/cpu/cpu8/online
  # echo 1 > /sys/devices/system/cpu/cpu8/online

  # 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
    /sys/devices/system/cpu/cpu8/cache/index1/shared_cpu_list: 8
    /sys/devices/system/cpu/cpu8/cache/index2/shared_cpu_list: 8
    /sys/devices/system/cpu/cpu8/cache/index3/shared_cpu_list: 8

  # cat /sys/devices/system/cpu/cpu72/cache/index0/shared_cpu_list
    72

  # cat /sys/devices/system/cpu/cpu72/cache/index3/shared_cpu_list
    0,2,4,6,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38,40,42,44,46,48,50,52,54,56,58,60,62,64,
    66,68,70,72,74,76,78,80,82,84,86,88,90,92,94,96,98,100,102,104,106,108,110,112,114,116,118,
    120,122,124,126

This patch addresses two issues associated with building
shared_cpu_list:

o Patch 1 fixes an ID matching issue that can lead to cacheinfo
  associating CPUs from different cache levels in case IDs are not
  unique across all the different cache levels. 

o Patch 2 clears the cpu_cacheinfo->cpu_map_populated flag when CPU goes
  offline and is removed from the shared_cpu_map.

Following are the results after applying the series on v6.3-rc5 on
respective x86 platforms:

o 3rd Generation AMD EPYC Processor (2 x 64C/128T)

  # 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
  # echo 1 > /sys/devices/system/cpu/cpu8/online
  
  # 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
  
  # cat /sys/devices/system/cpu/cpu136/cache/index0/shared_cpu_list
    8,136
  
  # cat /sys/devices/system/cpu/cpu136/cache/index3/shared_cpu_list
    8-15,136-143

o Intel Ice Lake Xeon (2 x 32C/128T)

  # 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: 8,72
    /sys/devices/system/cpu/cpu8/cache/index1/shared_cpu_list: 8,72
    /sys/devices/system/cpu/cpu8/cache/index2/shared_cpu_list: 8,72
    /sys/devices/system/cpu/cpu8/cache/index3/shared_cpu_list: 0,2,4,6,8,10,12,14,16,18,20,22,24,26,
    28,30,32,34,36,38,40,42,44,46,48,50,52,54,56,58,60,62,64,66,68,70,72,74,76,78,80,82,84,86,88,90,
    92,94,96,98,100,102,104,106,108,110,112,114,116,118,120,122,124,126
  
  # echo 0 > /sys/devices/system/cpu/cpu8/online
  # echo 1 > /sys/devices/system/cpu/cpu8/online
  
  # 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: 8,72
    /sys/devices/system/cpu/cpu8/cache/index1/shared_cpu_list: 8,72
    /sys/devices/system/cpu/cpu8/cache/index2/shared_cpu_list: 8,72
    /sys/devices/system/cpu/cpu8/cache/index3/shared_cpu_list: 0,2,4,6,8,10,12,14,16,18,20,22,24,26,
    28,30,32,34,36,38,40,42,44,46,48,50,52,54,56,58,60,62,64,66,68,70,72,74,76,78,80,82,84,86,88,90,
    92,94,96,98,100,102,104,106,108,110,112,114,116,118,120,122,124,126
  
  # cat /sys/devices/system/cpu/cpu72/cache/index0/shared_cpu_list
    8,72
  
  # cat /sys/devices/system/cpu/cpu72/cache/index3/shared_cpu_list
    0,2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38,40,42,44,46,48,50,52,54,56,58,60,62,64,66,
    68,70,72,74,76,78,80,82,84,86,88,90,92,94,96,98,100,102,104,106,108,110,112,114,116,118,120,122,
    124,126

Running "grep -r 'cpu_map_populated' arch/" shows MIPS and loongarch too
set the cpu_cacheinfo->cpu_map_populated who might also be affected by
the changes in commit 5c2712387d48 ("cacheinfo: Fix LLC is not exported
through sysfs") and this series. Changes from Patch 1 might also affect
RISC-V since Yong-Xuan Wang <yongxuan.wang@sifive.com> from SiFive last
made changes to cache_shared_cpu_map_setup() and
cache_shared_cpu_map_remove() in commit 198102c9103f ("cacheinfo: Fix
shared_cpu_map to handle shared caches at different levels").
---
K Prateek Nayak (2):
  drivers: base: cacheinfo: Fix shared_cpu_map changes in event of CPU
    hotplug
  drivers: base: cacheinfo: Clear cpu_map_populated when CPU goes
    offline

 drivers/base/cacheinfo.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

-- 
2.34.1