Re: [Qemu-devel] [PATCH] target-i386: adds PV_DEDICATED hint CPUID feature bit

[Eduardo Habkost <ehabkost@redhat.com>]

On Fri, Feb 09, 2018 at 08:24:26PM +0800, Wanpeng Li wrote:
> 2018-02-09 19:46 GMT+08:00 Eduardo Habkost <ehabkost@redhat.com>:
> > On Fri, Feb 09, 2018 at 09:41:41AM +0100, Paolo Bonzini wrote:
> >> On 08/02/2018 19:12, Eduardo Habkost wrote:
> >> > On Thu, Feb 08, 2018 at 05:44:20PM +0800, Wanpeng Li wrote:
> >> >> From: Wanpeng Li <wanpengli@tencent.com>
> >> >>
> >> >> Add PV_DEDICATED hint cpuid feature bit.
> >> >>
> >> > [...]
> >> >> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> >> >> index d70954b..cf48931 100644
> >> >> --- a/target/i386/cpu.c
> >> >> +++ b/target/i386/cpu.c
> >> >> @@ -4076,6 +4076,9 @@ static int x86_cpu_filter_features(X86CPU *cpu)
> >> >>              x86_cpu_get_supported_feature_word(w, false);
> >> >>          uint32_t requested_features = env->features[w];
> >> >>          env->features[w] &= host_feat;
> >> >> +        if (cpu->pv_dedicated && (w == FEAT_KVM)) {
> >> >> +            env->features[w] |= CPUID_PV_DEDICATED;
> >> >> +        }
> >> >
> >> > Why do this trick here instead of just adding "pv-dedicated" to
> >> > feature_word_info[FEAT_KVM].feat_names?
> >>
> >> I think because it can be added independent of KVM_GET_SUPPORTED_CPUID.
> >
> > If QEMU knows it can be enabled if outside GET_SUPPORTED_CPUID,
> > kvm_arch_get_supported_cpuid() can return it as supported.
> 
> The guest fails to detect the new cpuid this time.

This should fix it:

diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index a0aad808bd..44ee524188 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -804,6 +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);

> 
> 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..a0aad80 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 */
> 
> 
> Regards,
> Wanpeng Li

-- 
Eduardo