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Subject[PATCH] target/i386: add -cpu,lbr=true support to enable guest LBR
Date
The LBR feature would be enabled on the guest if:
- the KVM is enabled and the PMU is enabled and,
- the msr-based-feature IA32_PERF_CAPABILITIES is supporterd and,
- the supported returned value for lbr_fmt from this msr is not zero.

The LBR feature would be disabled on the guest if:
- the msr-based-feature IA32_PERF_CAPABILITIES is unsupporterd OR,
- qemu set the IA32_PERF_CAPABILITIES msr feature without lbr_fmt values OR,
- the requested guest vcpu model doesn't support PDCM.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: qemu-devel@nongnu.org
Signed-off-by: Like Xu <like.xu@linux.intel.com>
---
hw/i386/pc.c | 1 +
target/i386/cpu.c | 24 ++++++++++++++++++++++--
target/i386/cpu.h | 2 ++
target/i386/kvm.c | 7 ++++++-
4 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 3d419d5991..857aff75bb 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -318,6 +318,7 @@ GlobalProperty pc_compat_1_5[] = {
{ "Nehalem-" TYPE_X86_CPU, "min-level", "2" },
{ "virtio-net-pci", "any_layout", "off" },
{ TYPE_X86_CPU, "pmu", "on" },
+ { TYPE_X86_CPU, "lbr", "on" },
{ "i440FX-pcihost", "short_root_bus", "0" },
{ "q35-pcihost", "short_root_bus", "0" },
};
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 588f32e136..c803994887 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -1142,8 +1142,8 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
[FEAT_PERF_CAPABILITIES] = {
.type = MSR_FEATURE_WORD,
.feat_names = {
- NULL, NULL, NULL, NULL,
- NULL, NULL, NULL, NULL,
+ "lbr-fmt-bit-0", "lbr-fmt-bit-1", "lbr-fmt-bit-2", "lbr-fmt-bit-3",
+ "lbr-fmt-bit-4", "lbr-fmt-bit-5", NULL, NULL,
NULL, NULL, NULL, NULL,
NULL, "full-width-write", NULL, NULL,
NULL, NULL, NULL, NULL,
@@ -4224,6 +4224,12 @@ static bool lmce_supported(void)
return !!(mce_cap & MCG_LMCE_P);
}

+static inline bool lbr_supported(void)
+{
+ return kvm_enabled() && (kvm_arch_get_supported_msr_feature(kvm_state,
+ MSR_IA32_PERF_CAPABILITIES) & PERF_CAP_LBR_FMT);
+}
+
#define CPUID_MODEL_ID_SZ 48

/**
@@ -4327,6 +4333,9 @@ static void max_x86_cpu_initfn(Object *obj)
}

object_property_set_bool(OBJECT(cpu), "pmu", true, &error_abort);
+ if (lbr_supported()) {
+ object_property_set_bool(OBJECT(cpu), "lbr", true, &error_abort);
+ }
}

static const TypeInfo max_x86_cpu_type_info = {
@@ -5535,6 +5544,10 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
}
if (!cpu->enable_pmu) {
*ecx &= ~CPUID_EXT_PDCM;
+ if (cpu->enable_lbr) {
+ warn_report("LBR is unsupported since guest PMU is disabled.");
+ exit(1);
+ }
}
break;
case 2:
@@ -6553,6 +6566,12 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
}
}

+ if (!cpu->max_features && cpu->enable_lbr &&
+ !(env->features[FEAT_1_ECX] & CPUID_EXT_PDCM)) {
+ warn_report("requested vcpu model doesn't support PDCM for LBR.");
+ exit(1);
+ }
+
if (cpu->ucode_rev == 0) {
/* The default is the same as KVM's. */
if (IS_AMD_CPU(env)) {
@@ -7187,6 +7206,7 @@ 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_BOOL("lbr", X86CPU, enable_lbr, false),

DEFINE_PROP_UINT32("hv-spinlocks", X86CPU, hyperv_spinlock_attempts,
HYPERV_SPINLOCK_NEVER_RETRY),
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index e1a5c174dc..a059913e26 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -357,6 +357,7 @@ 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
@@ -1702,6 +1703,7 @@ struct X86CPU {
* capabilities) directly to the guest.
*/
bool enable_pmu;
+ bool enable_lbr;

/* LMCE support can be enabled/disabled via cpu option 'lmce=on/off'. It is
* disabled by default to avoid breaking migration between QEMU with
diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index b8455c89ed..feb33d5472 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -2690,8 +2690,10 @@ static void kvm_msr_entry_add_perf(X86CPU *cpu, FeatureWordArray f)
uint64_t kvm_perf_cap =
kvm_arch_get_supported_msr_feature(kvm_state,
MSR_IA32_PERF_CAPABILITIES);
-
if (kvm_perf_cap) {
+ if (!cpu->enable_lbr) {
+ kvm_perf_cap &= ~PERF_CAP_LBR_FMT;
+ }
kvm_msr_entry_add(cpu, MSR_IA32_PERF_CAPABILITIES,
kvm_perf_cap & f[FEAT_PERF_CAPABILITIES]);
}
@@ -2731,6 +2733,9 @@ static void kvm_init_msrs(X86CPU *cpu)

if (has_msr_perf_capabs && cpu->enable_pmu) {
kvm_msr_entry_add_perf(cpu, env->features);
+ } else if (!has_msr_perf_capabs && cpu->enable_lbr) {
+ warn_report("KVM doesn't support MSR_IA32_PERF_CAPABILITIES for LBR.");
+ exit(1);
}

if (has_msr_ucode_rev) {
--
2.21.3
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