linux-kernel - [PATCH v2 21/21] KVM: selftests: Verify LBRs are disabled if vPMU is disabled

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Date:   Fri, 10 Feb 2023 00:31:48 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Like Xu <like.xu.linux@...il.com>
Subject: [PATCH v2 21/21] KVM: selftests: Verify LBRs are disabled if vPMU is disabled

Verify that disabling the guest's vPMU via CPUID also disables LBRs.
KVM has had at least one bug where LBRs would remain enabled even though
the intent was to disable everything PMU related.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 .../selftests/kvm/x86_64/vmx_pmu_caps_test.c  | 29 +++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/tools/testing/selftests/kvm/x86_64/vmx_pmu_caps_test.c b/tools/testing/selftests/kvm/x86_64/vmx_pmu_caps_test.c
index 29aaa0419294..3009b3e5254d 100644
--- a/tools/testing/selftests/kvm/x86_64/vmx_pmu_caps_test.c
+++ b/tools/testing/selftests/kvm/x86_64/vmx_pmu_caps_test.c
@@ -204,6 +204,34 @@ static void test_immutable_perf_capabilities(union perf_capabilities host_cap)
 	kvm_vm_free(vm);
 }
 
+/*
+ * Test that LBR MSRs are writable when LBRs are enabled, and then verify that
+ * disabling the vPMU via CPUID also disables LBR support.  Set bits 2:0 of
+ * LBR_TOS as those bits are writable across all uarch implementations (arch
+ * LBRs will need to poke a different MSR).
+ */
+static void test_lbr_perf_capabilities(union perf_capabilities host_cap)
+{
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+	int r;
+
+	if (!host_cap.lbr_format)
+		return;
+
+	vm = vm_create_with_one_vcpu(&vcpu, NULL);
+
+	vcpu_set_msr(vcpu, MSR_IA32_PERF_CAPABILITIES, host_cap.capabilities);
+	vcpu_set_msr(vcpu, MSR_LBR_TOS, 7);
+
+	vcpu_clear_cpuid_entry(vcpu, X86_PROPERTY_PMU_VERSION.function);
+
+	r = _vcpu_set_msr(vcpu, MSR_LBR_TOS, 7);
+	TEST_ASSERT(!r, "Writing LBR_TOS should fail after disabling vPMU");
+
+	kvm_vm_free(vm);
+}
+
 int main(int argc, char *argv[])
 {
 	union perf_capabilities host_cap;
@@ -222,4 +250,5 @@ int main(int argc, char *argv[])
 	test_fungible_perf_capabilities(host_cap);
 	test_immutable_perf_capabilities(host_cap);
 	test_guest_wrmsr_perf_capabilities(host_cap);
+	test_lbr_perf_capabilities(host_cap);
 }
-- 
2.39.1.581.gbfd45094c4-goog