Until commit 5c271238 ("cacheinfo: Fix LLC is not exported through
sysfs"), cacheinfo called populate_cache_leaves() for CPU coming online
which let the arch specific functions handle (at least on x86)
populating the shared_cpu_map. However, with the changes in the
aforementioned commit, populate_cache_leaves() is not called when a CPU
comes online as a result of hotplug since last_level_cache_is_valid()
returns true as the cacheinfo data is not discarded. The CPU coming
online is not present in shared_cpu_map, however, it will not be added
since the cpu_cacheinfo->cpu_map_populated flag is set (it is set in
populate_cache_leaves() when cacheinfo is first populated for x86)

This can lead to inconsistencies in the shared_cpu_map when an offlined
CPU comes online again. Example below depicts the inconsistency in the
shared_cpu_list in cacheinfo when CPU8 is offlined and onlined again on
a 3rd Generation EPYC processor:

  # 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

Clear the flag when the CPU is removed from shared_cpu_map when
cache_shared_cpu_map_remove() is called during CPU hotplug. This will
allow cache_shared_cpu_map_setup() to add the CPU coming back online in
the shared_cpu_map. Set the flag again when the shared_cpu_map is setup.
Following are results of performing the same test as described above with
the 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: 8,136
    /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

Fixes: 5c271238 ("cacheinfo: Fix LLC is not exported through sysfs")
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Reviewed-by: Yicong Yang <yangyicong@hisilicon.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Link: https://lore.kernel.org/r/20230508084115.1157-3-kprateek.nayak@amd.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>