[Qemu-devel] [PATCH 2/2] target/i386: add -cpu,lbr=true support to enable guest LBR

[Like Xu]

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@xxxxxxxxxx>
Cc: Richard Henderson <rth@xxxxxxxxxxx>
Cc: Eduardo Habkost <ehabkost@xxxxxxxxxx>
Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
Cc: Marcel Apfelbaum <marcel.apfelbaum@xxxxxxxxx>
Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Cc: qemu-devel@xxxxxxxxxx
Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
---
 hw/i386/pc.c      |  1 +
 target/i386/cpu.c | 25 +++++++++++++++++++++++--
 target/i386/cpu.h |  2 ++
 target/i386/kvm.c |  7 ++++++-
 4 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 2128f3d6fe..8d8d42a8ea 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -316,6 +316,7 @@ 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 e47c9d1604..262a2595fa 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,
@@ -4187,6 +4187,13 @@ static bool lmce_supported(void)
     return !!(mce_cap & MCG_LMCE_P);
 }
 
+static inline bool lbr_supported(void)
+{
+    return kvm_enabled() && (PERF_CAP_LBR_FMT &
+        kvm_arch_get_supported_msr_feature(kvm_state,
+                                           MSR_IA32_PERF_CAPABILITIES));
+}
+
 #define CPUID_MODEL_ID_SZ 48
 
 /**
@@ -4290,6 +4297,9 @@ static void max_x86_cpu_initfn(Object *obj)
     }
 
     object_property_set_bool(OBJECT(cpu), true, "pmu", &error_abort);
+    if (lbr_supported()) {
+        object_property_set_bool(OBJECT(cpu), true, "lbr", &error_abort);
+    }
 }
 
 static const TypeInfo max_x86_cpu_type_info = {
@@ -5510,6 +5520,10 @@ 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:
@@ -6528,6 +6542,12 @@ 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)) {
@@ -7165,6 +7185,7 @@ 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 fad2f874bd..e5f65e9b0c 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
@@ -1686,6 +1687,7 @@ 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 9be6f76b2c..524ae86b0c 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -2652,8 +2652,10 @@ 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]);
     }
@@ -2693,6 +2695,9 @@ 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("host doesn't support MSR_IA32_PERF_CAPABILITIES for LBR.");
+        exit(1);
     }
 
     if (has_msr_ucode_rev) {
-- 
2.21.3