[PATCH v7 19/19] KVM: selftests: Test PMC virtualization with forced emulation

Sean Christopherson
2023-11-08T00:32:18Z

Extend the PMC counters test to use forced emulation to verify that KVM
emulates counter events for instructions retired and branches retired.
Force emulation for only a subset of the measured code to test that KVM
does the right thing when mixing perf events with emulated events.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
.../selftests/kvm/x86_64/pmu_counters_test.c | 44 +++++++++++++------
1 file changed, 30 insertions(+), 14 deletions(-)

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 d775cc7e8fab..09332b3c0a69 100644
--- a/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c
+++ b/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c
@@ -21,6 +21,7 @@

static uint8_t kvm_pmu_version;
static bool kvm_has_perf_caps;
+static bool is_forced_emulation_enabled;

static struct kvm_vm *pmu_vm_create_with_one_vcpu(struct kvm_vcpu **vcpu,
void *guest_code,
@@ -34,6 +35,7 @@ static struct kvm_vm *pmu_vm_create_with_one_vcpu(struct kvm_vcpu **vcpu,
vcpu_init_descriptor_tables(*vcpu);

sync_global_to_guest(vm, kvm_pmu_version);
+ sync_global_to_guest(vm, is_forced_emulation_enabled);

/*
* Set PERF_CAPABILITIES before PMU version as KVM disallows enabling
@@ -138,37 +140,50 @@ static void guest_assert_event_count(uint8_t idx,
* If CLFUSH{,OPT} is supported, flush the cacheline containing (at least) the
* start of the loop to force LLC references and misses, i.e. to allow testing
* that those events actually count.
+ *
+ * If forced emulation is enabled (and specified), force emulation on a subset
+ * of the measured code to verify that KVM correctly emulates instructions and
+ * branches retired events in conjunction with hardware also counting said
+ * events.
*/
-#define GUEST_MEASURE_EVENT(_msr, _value, clflush) \
+#define GUEST_MEASURE_EVENT(_msr, _value, clflush, FEP) \
do { \
__asm__ __volatile__("wrmsr\n\t" \
clflush "\n\t" \
"mfence\n\t" \
"1: mov $" __stringify(NUM_BRANCHES) ", %%ecx\n\t" \
- "loop .\n\t" \
- "mov %%edi, %%ecx\n\t" \
- "xor %%eax, %%eax\n\t" \
- "xor %%edx, %%edx\n\t" \
+ FEP "loop .\n\t" \
+ FEP "mov %%edi, %%ecx\n\t" \
+ FEP "xor %%eax, %%eax\n\t" \
+ FEP "xor %%edx, %%edx\n\t" \
"wrmsr\n\t" \
:: "a"((uint32_t)_value), "d"(_value >> 32), \
"c"(_msr), "D"(_msr) \
); \
} while (0)

+#define GUEST_TEST_EVENT(_idx, _event, _pmc, _pmc_msr, _ctrl_msr, _value, FEP) \
+do { \
+ wrmsr(pmc_msr, 0); \
+ \
+ if (this_cpu_has(X86_FEATURE_CLFLUSHOPT)) \
+ GUEST_MEASURE_EVENT(_ctrl_msr, _value, "clflushopt 1f", FEP); \
+ else if (this_cpu_has(X86_FEATURE_CLFLUSH)) \
+ GUEST_MEASURE_EVENT(_ctrl_msr, _value, "clflush 1f", FEP); \
+ else \
+ GUEST_MEASURE_EVENT(_ctrl_msr, _value, "nop", FEP); \
+ \
+ guest_assert_event_count(_idx, _event, _pmc, _pmc_msr); \
+} while (0)
+
static void __guest_test_arch_event(uint8_t idx, struct kvm_x86_pmu_feature event,
uint32_t pmc, uint32_t pmc_msr,
uint32_t ctrl_msr, uint64_t ctrl_msr_value)
{
- wrmsr(pmc_msr, 0);
+ GUEST_TEST_EVENT(idx, event, pmc, pmc_msr, ctrl_msr, ctrl_msr_value, "");

- if (this_cpu_has(X86_FEATURE_CLFLUSHOPT))
- GUEST_MEASURE_EVENT(ctrl_msr, ctrl_msr_value, "clflushopt 1f");
- else if (this_cpu_has(X86_FEATURE_CLFLUSH))
- GUEST_MEASURE_EVENT(ctrl_msr, ctrl_msr_value, "clflush 1f");
- else
- GUEST_MEASURE_EVENT(ctrl_msr, ctrl_msr_value, "nop");
-
- guest_assert_event_count(idx, event, pmc, pmc_msr);
+ if (is_forced_emulation_enabled)
+ GUEST_TEST_EVENT(idx, event, pmc, pmc_msr, ctrl_msr, ctrl_msr_value, KVM_FEP);
}

#define X86_PMU_FEATURE_NULL \
@@ -545,6 +560,7 @@ int main(int argc, char *argv[])

kvm_pmu_version = kvm_cpu_property(X86_PROPERTY_PMU_VERSION);
kvm_has_perf_caps = kvm_cpu_has(X86_FEATURE_PDCM);
+ is_forced_emulation_enabled = kvm_is_forced_emulation_enabled();

test_intel_counters();

--
2.42.0.869.gea05f2083d-goog