linux-kernel - [PATCH] x86: events: Do not return bogus capabilities if PMU is broken

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Message-Id: <20220601094256.362047-1-pbonzini@redhat.com>
Date:   Wed,  1 Jun 2022 05:42:56 -0400
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     peterz@...radead.org, x86@...nel.org, Like Xu <likexu@...cent.com>
Subject: [PATCH] x86: events: Do not return bogus capabilities if PMU is broken

From: Like Xu <likexu@...cent.com>

If the PMU is broken due to firmware issues, check_hw_exists() will return
false but perf_get_x86_pmu_capability() will still return data from x86_pmu.
Likewise if some of the hotplug callbacks cannot be installed the contents
of x86_pmu will not be reverted.

Handle the failure in both cases by clearing x86_pmu if init_hw_perf_events()
or reverts to software events only.

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/events/core.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 99cf67d63cf3..d23f3821daf5 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2095,14 +2095,15 @@ static int __init init_hw_perf_events(void)
 	}
 	if (err != 0) {
 		pr_cont("no PMU driver, software events only.\n");
-		return 0;
+		err = 0;
+		goto out_bad_pmu;
 	}
 
 	pmu_check_apic();
 
 	/* sanity check that the hardware exists or is emulated */
 	if (!check_hw_exists(&pmu, x86_pmu.num_counters, x86_pmu.num_counters_fixed))
-		return 0;
+		goto out_bad_pmu;
 
 	pr_cont("%s PMU driver.\n", x86_pmu.name);
 
@@ -2211,6 +2212,8 @@ static int __init init_hw_perf_events(void)
 	cpuhp_remove_state(CPUHP_AP_PERF_X86_STARTING);
 out:
 	cpuhp_remove_state(CPUHP_PERF_X86_PREPARE);
+out_bad_pmu:
+	memset(&x86_pmu, 0, sizeof(x86_pmu));
 	return err;
 }
 early_initcall(init_hw_perf_events);
@@ -2982,6 +2985,11 @@ unsigned long perf_misc_flags(struct pt_regs *regs)
 
 void perf_get_x86_pmu_capability(struct x86_pmu_capability *cap)
 {
+	if (!x86_pmu.name) {
+		memset(cap, 0, sizeof(*cap));
+		return;
+	}
+
 	cap->version		= x86_pmu.version;
 	/*
 	 * KVM doesn't support the hybrid PMU yet.
-- 
2.31.1