[PATCH v2] target-i386: add KVM_HINTS_DEDICATED performance hint

[Wanpeng Li]

From: Wanpeng Li <wanpengli@xxxxxxxxxxx>

Add KVM_HINTS_DEDICATED performance hint, guest checks this feature bit
to determine if they run on dedicated vCPUs, allowing optimizations such 
as usage of qspinlocks.  

Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
Cc: Eduardo Habkost <ehabkost@xxxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
---
v1 -> v2:
 * add a new feature word

 target/i386/cpu.c | 14 ++++++++++++++
 target/i386/cpu.h |  3 +++
 target/i386/kvm.c |  4 ++++
 3 files changed, 21 insertions(+)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index d70954b..e2974ad 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -358,6 +358,20 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
         .cpuid_eax = KVM_CPUID_FEATURES, .cpuid_reg = R_EAX,
         .tcg_features = TCG_KVM_FEATURES,
     },
+    [FEAT_KVM_HINTS] = {
+        .feat_names = {
+            "hint-dedicated", NULL, NULL, NULL,
+            NULL, NULL, NULL, NULL,
+            NULL, NULL, NULL, NULL,
+            NULL, NULL, NULL, NULL,
+            NULL, NULL, NULL, NULL,
+            NULL, NULL, NULL, NULL,
+            NULL, NULL, NULL, NULL,
+            NULL, NULL, NULL, NULL,
+        },
+        .cpuid_eax = KVM_CPUID_FEATURES, .cpuid_reg = R_EDX,
+        .tcg_features = TCG_KVM_FEATURES,
+    },
     [FEAT_HYPERV_EAX] = {
         .feat_names = {
             NULL /* hv_msr_vp_runtime_access */, NULL /* hv_msr_time_refcount_access */,
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index f91e37d..9f73692 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -475,6 +475,7 @@ typedef enum FeatureWord {
     FEAT_8000_0008_EBX, /* CPUID[8000_0008].EBX */
     FEAT_C000_0001_EDX, /* CPUID[C000_0001].EDX */
     FEAT_KVM,           /* CPUID[4000_0001].EAX (KVM_CPUID_FEATURES) */
+    FEAT_KVM_HINTS,     /* CPUID[4000_0001].EDX */
     FEAT_HYPERV_EAX,    /* CPUID[4000_0003].EAX */
     FEAT_HYPERV_EBX,    /* CPUID[4000_0003].EBX */
     FEAT_HYPERV_EDX,    /* CPUID[4000_0003].EDX */
@@ -670,6 +671,8 @@ typedef uint32_t FeatureWordArray[FEATURE_WORDS];
 #define CPUID_7_0_EDX_AVX512_4FMAPS (1U << 3) /* AVX512 Multiply Accumulation Single Precision */
 #define CPUID_7_0_EDX_SPEC_CTRL     (1U << 26) /* Speculation Control */
 
+#define KVM_HINTS_DEDICATED (1U << 0)
+
 #define CPUID_8000_0008_EBX_IBPB    (1U << 12) /* Indirect Branch Prediction Barrier */
 
 #define CPUID_XSAVE_XSAVEOPT   (1U << 0)
diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index ad4b159..44ee524 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -383,6 +383,9 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
         if (!kvm_irqchip_in_kernel()) {
             ret &= ~(1U << KVM_FEATURE_PV_UNHALT);
         }
+    } else if (function == KVM_CPUID_FEATURES && reg == R_EDX) {
+        ret |= KVM_HINTS_DEDICATED;
+        found = 1;
     }
 
     /* fallback for older kernels */
@@ -801,6 +804,7 @@ int kvm_arch_init_vcpu(CPUState *cs)
         c = &cpuid_data.entries[cpuid_i++];
         c->function = KVM_CPUID_FEATURES | kvm_base;
         c->eax = env->features[FEAT_KVM];
+        c->edx = env->features[FEAT_KVM_HINTS];
     }
 
     cpu_x86_cpuid(env, 0, 0, &limit, &unused, &unused, &unused);
-- 
2.7.4