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

[Wanpeng Li <kernellwp@gmail.com>]

2018-02-09 20:46 GMT+08:00 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);
>

Yeah, thanks, fold this in v2.

Regards,
Wanpeng Li

>>
>> 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