This unit-test is intended to test the KVM's support for the
Last Branch Recording (LBR) which is a performance monitor
unit (PMU) feature on Intel processors.
If the LBR bit is set to 1 in the DEBUGCTLMSR, the processor
will record a running trace of the most recent branches guest
taken in the LBR entries for guest to read.
This is a basic check that looks for the MSR LBR (via #GP check),
does some branches, and checks that the FROM_IP/TO_IP are good.
To run this test, use the QEMU option "-cpu host,migratable=no".
Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
---
x86/Makefile.common | 3 +-
x86/pmu_lbr.c | 121 ++++++++++++++++++++++++++++++++++++++++++++
x86/unittests.cfg | 6 +++
3 files changed, 129 insertions(+), 1 deletion(-)
create mode 100644 x86/pmu_lbr.c
diff --git a/x86/Makefile.common b/x86/Makefile.common
index 55f7f28..378a795 100644
--- a/x86/Makefile.common
+++ b/x86/Makefile.common
@@ -62,7 +62,8 @@ tests-common = $(TEST_DIR)/vmexit.flat $(TEST_DIR)/tsc.flat \
$(TEST_DIR)/init.flat $(TEST_DIR)/smap.flat \
$(TEST_DIR)/hyperv_synic.flat $(TEST_DIR)/hyperv_stimer.flat \
$(TEST_DIR)/hyperv_connections.flat \
- $(TEST_DIR)/umip.flat $(TEST_DIR)/tsx-ctrl.flat
+ $(TEST_DIR)/umip.flat $(TEST_DIR)/tsx-ctrl.flat \
+ $(TEST_DIR)/pmu_lbr.flat
test_cases: $(tests-common) $(tests)
diff --git a/x86/pmu_lbr.c b/x86/pmu_lbr.c
new file mode 100644
index 0000000..3bd9e9f
--- /dev/null
+++ b/x86/pmu_lbr.c
@@ -0,0 +1,121 @@
+#include "x86/msr.h"
+#include "x86/processor.h"
+#include "x86/desc.h"
+
+#define N 1000000
+#define MAX_NUM_LBR_ENTRY 32
+#define DEBUGCTLMSR_LBR (1UL << 0)
+#define PMU_CAP_LBR_FMT 0x3f
+
+#define MSR_LBR_NHM_FROM 0x00000680
+#define MSR_LBR_NHM_TO 0x000006c0
+#define MSR_LBR_CORE_FROM 0x00000040
+#define MSR_LBR_CORE_TO 0x00000060
+#define MSR_LBR_TOS 0x000001c9
+#define MSR_LBR_SELECT 0x000001c8
+
+volatile int count;
+
+static __attribute__((noinline)) int compute_flag(int i)
+{
+ if (i % 10 < 4)
+ return i + 1;
+ return 0;
+}
+
+static __attribute__((noinline)) int lbr_test(void)
+{
+ int i;
+ int flag;
+ volatile double x = 1212121212, y = 121212;
+
+ for (i = 0; i < 200000000; i++) {
+ flag = compute_flag(i);
+ count++;
+ if (flag)
+ x += x / y + y / x;
+ }
+ return 0;
+}
+
+union cpuid10_eax {
+ struct {
+ unsigned int version_id:8;
+ unsigned int num_counters:8;
+ unsigned int bit_width:8;
+ unsigned int mask_length:8;
+ } split;
+ unsigned int full;
+} eax;
+
+u32 lbr_from, lbr_to;
+
+static void init_lbr(void *index)
+{
+ wrmsr(lbr_from + *(int *) index, 0);
+ wrmsr(lbr_to + *(int *)index, 0);
+}
+
+static bool test_init_lbr_from_exception(u64 index)
+{
+ return test_for_exception(GP_VECTOR, init_lbr, &index);
+}
+
+int main(int ac, char **av)
+{
+ struct cpuid id = cpuid(10);
+ u64 perf_cap;
+ int max, i;
+
+ setup_vm();
+ perf_cap = rdmsr(MSR_IA32_PERF_CAPABILITIES);
+ eax.full = id.a;
+
+ if (!eax.split.version_id) {
+ printf("No pmu is detected!\n");
+ return report_summary();
+ }
+ if (!(perf_cap & PMU_CAP_LBR_FMT)) {
+ printf("No LBR is detected!\n");
+ return report_summary();
+ }
+
+ printf("PMU version: %d\n", eax.split.version_id);
+ printf("LBR version: %ld\n", perf_cap & PMU_CAP_LBR_FMT);
+
+ /* Look for LBR from and to MSRs */
+ lbr_from = MSR_LBR_CORE_FROM;
+ lbr_to = MSR_LBR_CORE_TO;
+ if (test_init_lbr_from_exception(0)) {
+ lbr_from = MSR_LBR_NHM_FROM;
+ lbr_to = MSR_LBR_NHM_TO;
+ }
+
+ if (test_init_lbr_from_exception(0)) {
+ printf("LBR on this platform is not supported!\n");
+ return report_summary();
+ }
+
+ wrmsr(MSR_LBR_SELECT, 0);
+ wrmsr(MSR_LBR_TOS, 0);
+ for (max = 0; max < MAX_NUM_LBR_ENTRY; max++) {
+ if (test_init_lbr_from_exception(max))
+ break;
+ }
+
+ report(max > 0, "The number of guest LBR entries is good.");
+
+ /* Do some branch instructions. */
+ wrmsr(MSR_IA32_DEBUGCTLMSR, DEBUGCTLMSR_LBR);
+ lbr_test();
+ wrmsr(MSR_IA32_DEBUGCTLMSR, 0);
+
+ report(rdmsr(MSR_LBR_TOS) != 0, "The guest LBR MSR_LBR_TOS value is good.");
+ for (i = 0; i < max; ++i) {
+ if (!rdmsr(lbr_to + i) || !rdmsr(lbr_from + i))
+ break;
+ }
+ report(i == max, "The guest LBR FROM_IP/TO_IP values are good.");
+
+ return report_summary();
+}
diff --git a/x86/unittests.cfg b/x86/unittests.cfg
index 90e370f..d0d46c7 100644
--- a/x86/unittests.cfg
+++ b/x86/unittests.cfg
@@ -174,6 +174,12 @@ file = pmu.flat
extra_params = -cpu max
check = /proc/sys/kernel/nmi_watchdog=0
+[pmu_lbr]
+file = pmu_lbr.flat
+extra_params = -cpu host,migratable=no
+check = /sys/module/kvm/parameters/ignore_msrs=N
+check = /proc/sys/kernel/nmi_watchdog=0
+
[vmware_backdoors]
file = vmware_backdoors.flat
extra_params = -machine vmport=on -cpu max
--
2.29.2
