linux-kernel - [PATCH] perf/x86/amd/uncore: Avoid PMU registration if counters are unavailable

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Date: Wed, 26 Jun 2024 13:14:04 +0530
From: Sandipan Das <sandipan.das@....com>
To: <linux-perf-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC: <x86@...nel.org>, <peterz@...radead.org>, <mingo@...nel.org>,
	<acme@...nel.org>, <namhyung@...nel.org>, <mark.rutland@....com>,
	<alexander.shishkin@...ux.intel.com>, <jolsa@...nel.org>,
	<irogers@...gle.com>, <adrian.hunter@...el.com>, <kan.liang@...ux.intel.com>,
	<tglx@...utronix.de>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>,
	<hpa@...or.com>, <ravi.bangoria@....com>, <ananth.narayan@....com>,
	<sandipan.das@....com>
Subject: [PATCH] perf/x86/amd/uncore: Avoid PMU registration if counters are unavailable

X86_FEATURE_PERFCTR_NB and X86_FEATURE_PERFCTR_LLC are derived from
CPUID leaf 0x80000001 ECX bits 24 and 28 respectively and denote the
availability of DF and L3 counters. When these bits are not set, the
corresponding PMUs have no counters and hence, should not be registered.

Fixes: 07888daa056e ("perf/x86/amd/uncore: Move discovery and registration")
Signed-off-by: Sandipan Das <sandipan.das@....com>
---
 arch/x86/events/amd/uncore.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/arch/x86/events/amd/uncore.c b/arch/x86/events/amd/uncore.c
index 4ccb8fa483e6..b78e05ab4a73 100644
--- a/arch/x86/events/amd/uncore.c
+++ b/arch/x86/events/amd/uncore.c
@@ -654,17 +654,20 @@ int amd_uncore_df_ctx_init(struct amd_uncore *uncore, unsigned int cpu)
 {
 	struct attribute **df_attr = amd_uncore_df_format_attr;
 	struct amd_uncore_pmu *pmu;
+	int num_counters;
 
 	/* Run just once */
 	if (uncore->init_done)
 		return amd_uncore_ctx_init(uncore, cpu);
 
+	num_counters = amd_uncore_ctx_num_pmcs(uncore, cpu);
+	if (!num_counters)
+		goto done;
+
 	/* No grouping, single instance for a system */
 	uncore->pmus = kzalloc(sizeof(*uncore->pmus), GFP_KERNEL);
-	if (!uncore->pmus) {
-		uncore->num_pmus = 0;
+	if (!uncore->pmus)
 		goto done;
-	}
 
 	/*
 	 * For Family 17h and above, the Northbridge counters are repurposed
@@ -674,7 +677,7 @@ int amd_uncore_df_ctx_init(struct amd_uncore *uncore, unsigned int cpu)
 	pmu = &uncore->pmus[0];
 	strscpy(pmu->name, boot_cpu_data.x86 >= 0x17 ? "amd_df" : "amd_nb",
 		sizeof(pmu->name));
-	pmu->num_counters = amd_uncore_ctx_num_pmcs(uncore, cpu);
+	pmu->num_counters = num_counters;
 	pmu->msr_base = MSR_F15H_NB_PERF_CTL;
 	pmu->rdpmc_base = RDPMC_BASE_NB;
 	pmu->group = amd_uncore_ctx_gid(uncore, cpu);
@@ -785,17 +788,20 @@ int amd_uncore_l3_ctx_init(struct amd_uncore *uncore, unsigned int cpu)
 {
 	struct attribute **l3_attr = amd_uncore_l3_format_attr;
 	struct amd_uncore_pmu *pmu;
+	int num_counters;
 
 	/* Run just once */
 	if (uncore->init_done)
 		return amd_uncore_ctx_init(uncore, cpu);
 
+	num_counters = amd_uncore_ctx_num_pmcs(uncore, cpu);
+	if (!num_counters)
+		goto done;
+
 	/* No grouping, single instance for a system */
 	uncore->pmus = kzalloc(sizeof(*uncore->pmus), GFP_KERNEL);
-	if (!uncore->pmus) {
-		uncore->num_pmus = 0;
+	if (!uncore->pmus)
 		goto done;
-	}
 
 	/*
 	 * For Family 17h and above, L3 cache counters are available instead
@@ -805,7 +811,7 @@ int amd_uncore_l3_ctx_init(struct amd_uncore *uncore, unsigned int cpu)
 	pmu = &uncore->pmus[0];
 	strscpy(pmu->name, boot_cpu_data.x86 >= 0x17 ? "amd_l3" : "amd_l2",
 		sizeof(pmu->name));
-	pmu->num_counters = amd_uncore_ctx_num_pmcs(uncore, cpu);
+	pmu->num_counters = num_counters;
 	pmu->msr_base = MSR_F16H_L2I_PERF_CTL;
 	pmu->rdpmc_base = RDPMC_BASE_LLC;
 	pmu->group = amd_uncore_ctx_gid(uncore, cpu);
-- 
2.43.0