[PATCH v4 6/9] KVM: selftests: Test consistency of CPUID with num of gp counters

[Jinrong Liang]

From: Jinrong Liang <cloudliang@xxxxxxxxxxx>

Add test to check if non-existent counters can be accessed in guest after
determining the number of Intel generic performance counters by CPUID.
When the num of counters is less than 3, KVM does not emulate #GP if
a counter isn't present due to compatibility MSR_P6_PERFCTRx handling.
Nor will the KVM emulate more counters than it can support.

Co-developed-by: Like Xu <likexu@xxxxxxxxxxx>
Signed-off-by: Like Xu <likexu@xxxxxxxxxxx>
Signed-off-by: Jinrong Liang <cloudliang@xxxxxxxxxxx>
---
 .../selftests/kvm/x86_64/pmu_counters_test.c  | 85 +++++++++++++++++++
 1 file changed, 85 insertions(+)

diff --git a/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c b/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c
index fe9f38a3557e..e636323e202c 100644
--- a/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c
+++ b/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c
@@ -17,6 +17,11 @@
 /* Guest payload for any performance counter counting */
 #define NUM_BRANCHES		10
 
+static const uint64_t perf_caps[] = {
+	0,
+	PMU_CAP_FW_WRITES,
+};
+
 static struct kvm_vm *pmu_vm_create_with_one_vcpu(struct kvm_vcpu **vcpu,
 						  void *guest_code)
 {
@@ -189,6 +194,85 @@ static void test_intel_arch_events(void)
 	}
 }
 
+static void __guest_wrmsr_rdmsr(uint32_t counter_msr, uint8_t nr_msrs,
+				bool expect_gp)
+{
+	uint64_t msr_val;
+	uint8_t vector;
+
+	vector = wrmsr_safe(counter_msr + nr_msrs, 0xffff);
+	__GUEST_ASSERT(expect_gp ? vector == GP_VECTOR : !vector,
+		       "Expected GP_VECTOR");
+
+	vector = rdmsr_safe(counter_msr + nr_msrs, &msr_val);
+	__GUEST_ASSERT(expect_gp ? vector == GP_VECTOR : !vector,
+		       "Expected GP_VECTOR");
+
+	if (!expect_gp)
+		GUEST_ASSERT_EQ(msr_val, 0);
+
+	GUEST_DONE();
+}
+
+static void guest_rd_wr_gp_counter(void)
+{
+	uint8_t nr_gp_counters = this_cpu_property(X86_PROPERTY_PMU_NR_GP_COUNTERS);
+	uint64_t perf_capabilities = rdmsr(MSR_IA32_PERF_CAPABILITIES);
+	uint32_t counter_msr;
+	bool expect_gp = true;
+
+	if (perf_capabilities & PMU_CAP_FW_WRITES) {
+		counter_msr = MSR_IA32_PMC0;
+	} else {
+		counter_msr = MSR_IA32_PERFCTR0;
+
+		/* KVM drops writes to MSR_P6_PERFCTR[0|1]. */
+		if (nr_gp_counters == 0)
+			expect_gp = false;
+	}
+
+	__guest_wrmsr_rdmsr(counter_msr, nr_gp_counters, expect_gp);
+}
+
+/* Access the first out-of-range counter register to trigger #GP */
+static void test_oob_gp_counter(uint8_t eax_gp_num, uint64_t perf_cap)
+{
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+
+	vm = pmu_vm_create_with_one_vcpu(&vcpu, guest_rd_wr_gp_counter);
+
+	vcpu_set_cpuid_property(vcpu, X86_PROPERTY_PMU_NR_GP_COUNTERS,
+				eax_gp_num);
+	vcpu_set_msr(vcpu, MSR_IA32_PERF_CAPABILITIES, perf_cap);
+
+	run_vcpu(vcpu);
+
+	kvm_vm_free(vm);
+}
+
+static void test_intel_counters_num(void)
+{
+	uint8_t nr_gp_counters = kvm_cpu_property(X86_PROPERTY_PMU_NR_GP_COUNTERS);
+	unsigned int i;
+
+	TEST_REQUIRE(nr_gp_counters > 2);
+
+	for (i = 0; i < ARRAY_SIZE(perf_caps); i++) {
+		/*
+		 * For compatibility reasons, KVM does not emulate #GP
+		 * when MSR_P6_PERFCTR[0|1] is not present, but it doesn't
+		 * affect checking the presence of MSR_IA32_PMCx with #GP.
+		 */
+		test_oob_gp_counter(0, perf_caps[i]);
+		test_oob_gp_counter(2, perf_caps[i]);
+		test_oob_gp_counter(nr_gp_counters, perf_caps[i]);
+
+		/* KVM doesn't emulate more counters than it can support. */
+		test_oob_gp_counter(nr_gp_counters + 1, perf_caps[i]);
+	}
+}
+
 int main(int argc, char *argv[])
 {
 	TEST_REQUIRE(get_kvm_param_bool("enable_pmu"));
@@ -199,6 +283,7 @@ int main(int argc, char *argv[])
 	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_PDCM));
 
 	test_intel_arch_events();
+	test_intel_counters_num();
 
 	return 0;
 }
-- 
2.39.3