The Last Branch Recording (LBR) is a performance monitor unit (PMU)
feature on Intel processors which records a running trace of the most
recent branches taken by the processor in the LBR stack. This option
indicates the LBR format to enable for guest perf.
The LBR feature is enabled if below conditions are met:
1) KVM is enabled and the PMU is enabled.
2) msr-based-feature IA32_PERF_CAPABILITIES is supporterd on KVM.
3) Supported returned value for lbr_fmt from above msr is non-zero.
4) Guest vcpu model does support FEAT_1_ECX.CPUID_EXT_PDCM.
5) User-provided lbr-fmt value doesn't violate its bitmask (0x3f).
6) Target guest LBR format matches that of host.
Co-developed-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
---
target/i386/cpu.c | 40 ++++++++++++++++++++++++++++++++++++++++
target/i386/cpu.h | 10 ++++++++++
2 files changed, 50 insertions(+)
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index aa9e636800..55eb519214 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -6280,6 +6280,7 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
CPUX86State *env = &cpu->env;
Error *local_err = NULL;
static bool ht_warned;
+ uint64_t requested_lbr_fmt;
if (cpu->apic_id == UNASSIGNED_APIC_ID) {
error_setg(errp, "apic-id property was not initialized properly");
@@ -6297,6 +6298,42 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
goto out;
}
+ /*
+ * Override env->features[FEAT_PERF_CAPABILITIES].LBR_FMT
+ * with user-provided setting.
+ */
+ if (cpu->lbr_fmt != ~PERF_CAP_LBR_FMT) {
+ if ((cpu->lbr_fmt & PERF_CAP_LBR_FMT) != cpu->lbr_fmt) {
+ error_setg(errp, "invalid lbr-fmt");
+ return;
+ }
+ env->features[FEAT_PERF_CAPABILITIES] &= ~PERF_CAP_LBR_FMT;
+ env->features[FEAT_PERF_CAPABILITIES] |= cpu->lbr_fmt;
+ }
+
+ /*
+ * vPMU LBR is supported when 1) KVM is enabled 2) Option pmu=on and
+ * 3)vPMU LBR format matches that of host setting.
+ */
+ requested_lbr_fmt =
+ env->features[FEAT_PERF_CAPABILITIES] & PERF_CAP_LBR_FMT;
+ if (requested_lbr_fmt && kvm_enabled()) {
+ uint64_t host_perf_cap =
+ x86_cpu_get_supported_feature_word(FEAT_PERF_CAPABILITIES, false);
+ uint64_t host_lbr_fmt = host_perf_cap & PERF_CAP_LBR_FMT;
+
+ if (!cpu->enable_pmu) {
+ error_setg(errp, "vPMU: LBR is unsupported without pmu=on");
+ return;
+ }
+ if (requested_lbr_fmt != host_lbr_fmt) {
+ error_setg(errp, "vPMU: the lbr-fmt value (0x%lx) mismatches "
+ "the host supported value (0x%lx).",
+ requested_lbr_fmt, host_lbr_fmt);
+ return;
+ }
+ }
+
x86_cpu_filter_features(cpu, cpu->check_cpuid || cpu->enforce_cpuid);
if (cpu->enforce_cpuid && x86_cpu_have_filtered_features(cpu)) {
@@ -6649,6 +6686,8 @@ static void x86_cpu_initfn(Object *obj)
object_property_add_alias(obj, "sse4_2", obj, "sse4.2");
object_property_add_alias(obj, "hv-apicv", obj, "hv-avic");
+ cpu->lbr_fmt = ~PERF_CAP_LBR_FMT;
+ object_property_add_alias(obj, "lbr_fmt", obj, "lbr-fmt");
if (xcc->model) {
x86_cpu_load_model(cpu, xcc->model);
@@ -6804,6 +6843,7 @@ static Property x86_cpu_properties[] = {
#endif
DEFINE_PROP_INT32("node-id", X86CPU, node_id, CPU_UNSET_NUMA_NODE_ID),
DEFINE_PROP_BOOL("pmu", X86CPU, enable_pmu, false),
+ DEFINE_PROP_UINT64_CHECKMASK("lbr-fmt", X86CPU, lbr_fmt, PERF_CAP_LBR_FMT),
DEFINE_PROP_UINT32("hv-spinlocks", X86CPU, hyperv_spinlock_attempts,
HYPERV_SPINLOCK_NEVER_NOTIFY),
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 9911d7c871..ee8974abc9 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -383,6 +383,7 @@ typedef enum X86Seg {
#define ARCH_CAP_TSX_CTRL_MSR (1<<7)
#define MSR_IA32_PERF_CAPABILITIES 0x345
+#define PERF_CAP_LBR_FMT 0x3f
#define MSR_IA32_TSX_CTRL 0x122
#define MSR_IA32_TSCDEADLINE 0x6e0
@@ -1775,6 +1776,15 @@ struct X86CPU {
*/
bool enable_pmu;
+ /*
+ * Enable LBR_FMT bits of IA32_PERF_CAPABILITIES MSR.
+ * This can't be initialized with a default because it doesn't have
+ * stable ABI support yet. It is only allowed to pass all LBR_FMT bits
+ * returned by kvm_arch_get_supported_msr_feature()(which depends on both
+ * host CPU and kernel capabilities) to the guest.
+ */
+ uint64_t lbr_fmt;
+
/* LMCE support can be enabled/disabled via cpu option 'lmce=on/off'. It is
* disabled by default to avoid breaking migration between QEMU with
* different LMCE configurations.
--
2.27.0
