Re: [PATCH RFC 22/22] i386: expand Hyper-V features early

[Eduardo Habkost <ehabkost@redhat.com>]

On Fri, Sep 04, 2020 at 04:54:31PM +0200, Vitaly Kuznetsov wrote:
> To make Hyper-V features appear in e.g. QMP query-cpu-model-expansion we
> need to expand and set the corresponding CPUID leaves early. Modify
> x86_cpu_get_supported_feature_word() to call newly intoduced Hyper-V
> specific kvm_hv_get_supported_cpuid() instead of
> kvm_arch_get_supported_cpuid(). We can't use kvm_arch_get_supported_cpuid()
> as Hyper-V specific CPUID leaves intersect with KVM's.
> 
> Note, early expansion will only happen when KVM supports system wide
> KVM_GET_SUPPORTED_HV_CPUID ioctl (KVM_CAP_SYS_HYPERV_CPUID).

Will this implicitly enable hyperv CPUID passthrough when using
"-cpu host"?  Do we want it to?

> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  target/i386/cpu.c      | 15 +++++++++------
>  target/i386/kvm.c      | 15 +++++++++++++++
>  target/i386/kvm_i386.h |  7 +++++++
>  3 files changed, 31 insertions(+), 6 deletions(-)
> 
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 479c4bbbf459..d3c4ecb3535c 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -5147,7 +5147,7 @@ CpuDefinitionInfoList *qmp_query_cpu_definitions(Error **errp)
>      return cpu_list;
>  }
>  
> -static uint64_t x86_cpu_get_supported_feature_word(FeatureWord w,
> +static uint64_t x86_cpu_get_supported_feature_word(X86CPU *cpu, FeatureWord w,
>                                                     bool migratable_only)
>  {
>      FeatureWordInfo *wi = &feature_word_info[w];
> @@ -5156,9 +5156,12 @@ static uint64_t x86_cpu_get_supported_feature_word(FeatureWord w,
>      if (kvm_enabled()) {
>          switch (wi->type) {
>          case CPUID_FEATURE_WORD:
> -            r = kvm_arch_get_supported_cpuid(kvm_state, wi->cpuid.eax,
> -                                                        wi->cpuid.ecx,
> -                                                        wi->cpuid.reg);
> +            if (hyperv_feature_word(w))
> +                r = kvm_hv_get_supported_cpuid(cpu, w);
> +            else
> +                r = kvm_arch_get_supported_cpuid(kvm_state, wi->cpuid.eax,
> +                                                 wi->cpuid.ecx,
> +                                                 wi->cpuid.reg);
>              break;
>          case MSR_FEATURE_WORD:
>              r = kvm_arch_get_supported_msr_feature(kvm_state,
> @@ -6485,7 +6488,7 @@ static void x86_cpu_expand_features(X86CPU *cpu, Error **errp)
>               * by the user.
>               */
>              env->features[w] |=
> -                x86_cpu_get_supported_feature_word(w, cpu->migratable) &
> +                x86_cpu_get_supported_feature_word(cpu, w, cpu->migratable) &
>                  ~env->user_features[w] &
>                  ~feature_word_info[w].no_autoenable_flags;
>          }
> @@ -6589,7 +6592,7 @@ static void x86_cpu_filter_features(X86CPU *cpu, bool verbose)
>  
>      for (w = 0; w < FEATURE_WORDS; w++) {
>          uint64_t host_feat =
> -            x86_cpu_get_supported_feature_word(w, false);
> +            x86_cpu_get_supported_feature_word(cpu, w, false);
>          uint64_t requested_features = env->features[w];
>          uint64_t unavailable_features = requested_features & ~host_feat;
>          mark_unavailable_features(cpu, w, unavailable_features, prefix);
> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> index 961241528a5c..764b96fbbb7d 100644
> --- a/target/i386/kvm.c
> +++ b/target/i386/kvm.c
> @@ -1449,6 +1449,21 @@ static int hyperv_fill_cpuids(CPUState *cs,
>      return cpuid_i;
>  }
>  
> +uint32_t kvm_hv_get_supported_cpuid(X86CPU *cpu, enum FeatureWord w)
> +{
> +    CPUState *cs = CPU(cpu);
> +    CPUX86State *env = &cpu->env;
> +    Error *local_err = NULL;
> +
> +    hyperv_expand_features(cs, &local_err);
> +
> +    if (local_err) {
> +            error_report_err(local_err);
> +    }
> +
> +    return env->features[w];
> +}
> +
>  static Error *hv_passthrough_mig_blocker;
>  static Error *hv_no_nonarch_cs_mig_blocker;
>  
> diff --git a/target/i386/kvm_i386.h b/target/i386/kvm_i386.h
> index 064b8798a26c..2e7da4f39668 100644
> --- a/target/i386/kvm_i386.h
> +++ b/target/i386/kvm_i386.h
> @@ -48,4 +48,11 @@ bool kvm_has_waitpkg(void);
>  
>  bool kvm_hv_vpindex_settable(void);
>  
> +static inline bool hyperv_feature_word(enum FeatureWord w)
> +{
> +    return w >= FEAT_HYPERV_EAX && w <= FEAT_HV_NESTED_EDX;
> +}
> +
> +uint32_t kvm_hv_get_supported_cpuid(X86CPU *cpu, enum FeatureWord w);
> +
>  #endif
> -- 
> 2.25.4
> 

-- 
Eduardo