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.

Link: https://lore.kernel.org/r/20230311004618.920745-22-seanjc@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>

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);
 }