linux-kernel - [PATCH 6.1 09/10] drivers: base: cacheinfo: Update cpu_map

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Message-Id: <20251020173624.20228-10-wen.yang@linux.dev>
Date: Tue, 21 Oct 2025 01:36:23 +0800
From: Wen Yang <wen.yang@...ux.dev>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jon Hunter <jonathanh@...dia.com>
Cc: stable@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	K Prateek Nayak <kprateek.nayak@....com>,
	Yicong Yang <yangyicong@...ilicon.com>,
	Sudeep Holla <sudeep.holla@....com>,
	Wen Yang <wen.yang@...ux.dev>
Subject: [PATCH 6.1 09/10] drivers: base: cacheinfo: Update cpu_map_populated during CPU Hotplug

From: K Prateek Nayak <kprateek.nayak@....com>

[ Upstream commit c26fabe73330d983c7ce822c6b6ec0879b4da61f ]

Until commit 5c2712387d48 ("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: 5c2712387d48 ("cacheinfo: Fix LLC is not exported through sysfs")
Signed-off-by: K Prateek Nayak <kprateek.nayak@....com>
Reviewed-by: Yicong Yang <yangyicong@...ilicon.com>
Reviewed-by: Sudeep Holla <sudeep.holla@....com>
Link: https://lore.kernel.org/r/20230508084115.1157-3-kprateek.nayak@amd.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Wen Yang <wen.yang@...ux.dev>
---
 drivers/base/cacheinfo.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
index 60ecf7cc0250..9e11d42b0d64 100644
--- a/drivers/base/cacheinfo.c
+++ b/drivers/base/cacheinfo.c
@@ -365,11 +365,14 @@ static int cache_shared_cpu_map_setup(unsigned int cpu)
 			coherency_max_size = this_leaf->coherency_line_size;
 	}
 
+	/* shared_cpu_map is now populated for the cpu */
+	this_cpu_ci->cpu_map_populated = true;
 	return 0;
 }
 
 static void cache_shared_cpu_map_remove(unsigned int cpu)
 {
+	struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);
 	struct cacheinfo *this_leaf, *sib_leaf;
 	unsigned int sibling, index, sib_index;
 
@@ -404,6 +407,9 @@ static void cache_shared_cpu_map_remove(unsigned int cpu)
 		if (of_have_populated_dt())
 			of_node_put(this_leaf->fw_token);
 	}
+
+	/* cpu is no longer populated in the shared map */
+	this_cpu_ci->cpu_map_populated = false;
 }
 
 static void free_cache_attributes(unsigned int cpu)
-- 
2.25.1