Re: [PATCH v6 15/19] i386: expand Hyper-V features during CPU feature expansion time

[Eduardo Habkost]

On Thu, Apr 22, 2021 at 06:11:26PM +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).
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  target/i386/cpu.c          |  4 ++++
>  target/i386/kvm/kvm-stub.c |  5 +++++
>  target/i386/kvm/kvm.c      | 15 ++++++++++++---
>  target/i386/kvm/kvm_i386.h |  1 +
>  4 files changed, 22 insertions(+), 3 deletions(-)
> 
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index d72b8760e7a3..18b57f3d8b9c 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -6514,6 +6514,10 @@ static void x86_cpu_expand_features(X86CPU *cpu, Error 
> **errp)
>      if (env->cpuid_xlevel2 == UINT32_MAX) {
>          env->cpuid_xlevel2 = env->cpuid_min_xlevel2;
>      }
> +
> +    if (kvm_enabled()) {
> +        kvm_hyperv_expand_features(cpu, errp);
> +    }
>  }
>  
>  /*
> diff --git a/target/i386/kvm/kvm-stub.c b/target/i386/kvm/kvm-stub.c
> index 92f49121b8fa..7f175faa3abd 100644
> --- a/target/i386/kvm/kvm-stub.c
> +++ b/target/i386/kvm/kvm-stub.c
> @@ -39,3 +39,8 @@ bool kvm_hv_vpindex_settable(void)
>  {
>      return false;
>  }
> +
> +void kvm_hyperv_expand_features(X86CPU *cpu, Error **errp)
> +{
> +    return;

Maybe we should make it abort()?  This function should never be
called if KVM is disabled.

> +}
> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> index a42263b24fca..d5551c4ab5cf 100644
> --- a/target/i386/kvm/kvm.c
> +++ b/target/i386/kvm/kvm.c
> @@ -1216,13 +1216,22 @@ static uint32_t hv_build_cpuid_leaf(CPUState *cs, 
> uint32_t func, int reg)
>   * of 'hv_passthrough' mode and fills the environment with all supported
>   * Hyper-V features.
>   */
> -static void hyperv_expand_features(CPUState *cs, Error **errp)
> +void kvm_hyperv_expand_features(X86CPU *cpu, Error **errp)
>  {
> -    X86CPU *cpu = X86_CPU(cs);
> +    CPUState *cs = CPU(cpu);
>  
>      if (!hyperv_enabled(cpu))
>          return;
>  
> +    /*
> +     * When kvm_hyperv_expand_features is called at CPU feature expansion
> +     * time per-CPU kvm_state is not available yet so we can only proceed
> +     * when KVM_CAP_SYS_HYPERV_CPUID is supported.
> +     */
> +    if (!cs->kvm_state &&
> +        !kvm_check_extension(kvm_state, KVM_CAP_SYS_HYPERV_CPUID))
> +        return;
> +
>      if (cpu->hyperv_passthrough) {
>          cpu->hyperv_vendor_id[0] =
>              hv_cpuid_get_host(cs, HV_CPUID_VENDOR_AND_MAX_FUNCTIONS, R_EBX);
> @@ -1556,7 +1565,7 @@ int kvm_arch_init_vcpu(CPUState *cs)
>      env->apic_bus_freq = KVM_APIC_BUS_FREQUENCY;
>  
>      /* Paravirtualization CPUIDs */
> -    hyperv_expand_features(cs, &local_err);
> +    kvm_hyperv_expand_features(cpu, &local_err);

Do we still need to call the function again here?

If the first expansion isn't expanding everything, I'm afraid
this second call will hide bugs in query-cpu-model-expansion.


>      if (local_err) {
>          error_report_err(local_err);
>          return -ENOSYS;
> diff --git a/target/i386/kvm/kvm_i386.h b/target/i386/kvm/kvm_i386.h
> index dc725083891c..f1176491051d 100644
> --- a/target/i386/kvm/kvm_i386.h
> +++ b/target/i386/kvm/kvm_i386.h
> @@ -47,6 +47,7 @@ bool kvm_has_x2apic_api(void);
>  bool kvm_has_waitpkg(void);
>  
>  bool kvm_hv_vpindex_settable(void);
> +void kvm_hyperv_expand_features(X86CPU *cpu, Error **errp);
>  
>  uint64_t kvm_swizzle_msi_ext_dest_id(uint64_t address);
>  
> -- 
> 2.30.2
> 

-- 
Eduardo