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Subject[PATCH v2] target-i386: add KVM_HINTS_DEDICATED performance hint
Date
From: Wanpeng Li <wanpengli@tencent.com>

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@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
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
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