linux-kernel - [PATCH] x86/cacheinfo: Don't use cpu_llc_shared_map for !CONFIG

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Date:   Wed, 10 Aug 2022 09:15:15 -0700
From:   Saurabh Sengar <ssengar@...ux.microsoft.com>
To:     ssengar@...rosoft.com, mikelley@...rosoft.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, peterz@...radead.org,
        tim.c.chen@...ux.intel.com, will@...nel.org,
        song.bao.hua@...ilicon.com, suravee.suthikulpanit@....com,
        linux-kernel@...r.kernel.org
Subject: [PATCH] x86/cacheinfo: Don't use cpu_llc_shared_map for !CONFIG_SMP

cpu_llc_shared_map is always declared and defined, but populated in
arch/x86/kernel/smpboot.c which only builds for CONFIG_SMP=y. For
UniProcessor builds this mask is never populated and hence invalid.
Current code doesn't handle the case of AMD UniProcessor correctly,
which results "shared_cpu_map" and "shared_cpu_list" files missing from
sysfs entries for l3 cache. This patch fixes this issue.
This code used to work because of a another bug in 'cpumask_next',
where in the CONFIG_SMP=n case the cpumask_next() ignores empty mask
that results as if CPU 0 was set. This bug in 'cpumask_next' was fixed by
following commit, which exposes the cpu_llc_shared_map bug.

b81dce77ced ("cpumask: Fix invalid uniprocessor mask assumption")

Fixes: 2b83809a5e ("x86/cpu/amd: Derive L3 shared_cpu_map from cpu_llc_shared_mask")
Signed-off-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
---
 arch/x86/kernel/cpu/cacheinfo.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/cacheinfo.c b/arch/x86/kernel/cpu/cacheinfo.c
index 66556833d7af..8753bf33fec4 100644
--- a/arch/x86/kernel/cpu/cacheinfo.c
+++ b/arch/x86/kernel/cpu/cacheinfo.c
@@ -889,10 +889,12 @@ static int __cache_amd_cpumap_setup(unsigned int cpu, int index,
 	int i, sibling;
 
 	/*
-	 * For L3, always use the pre-calculated cpu_llc_shared_mask
-	 * to derive shared_cpu_map.
+	 * For L3, in case of SMP systems use the pre-calculated
+	 * cpu_llc_shared_mask to derive shared_cpu_map. In case
+	 * of UP simply set the only cpu in mask.
 	 */
 	if (index == 3) {
+#ifdef CONFIG_SMP
 		for_each_cpu(i, cpu_llc_shared_mask(cpu)) {
 			this_cpu_ci = get_cpu_cacheinfo(i);
 			if (!this_cpu_ci->info_list)
@@ -905,6 +907,14 @@ static int __cache_amd_cpumap_setup(unsigned int cpu, int index,
 						&this_leaf->shared_cpu_map);
 			}
 		}
+#else
+		this_cpu_ci = get_cpu_cacheinfo(cpu);
+		WARN_ON(!this_cpu_ci->info_list);
+		if (!this_cpu_ci->info_list)
+			return 0;
+		this_leaf = this_cpu_ci->info_list + index;
+		cpumask_set_cpu(cpu, &this_leaf->shared_cpu_map);
+#endif
 	} else if (boot_cpu_has(X86_FEATURE_TOPOEXT)) {
 		unsigned int apicid, nshared, first, last;
 
-- 
2.25.1