linux-kernel - Re: [PATCH v4 09/25] KVM: VMX: nVMX: Support TSC scaling and PERF_GLOBAL

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Date:   Mon, 25 Jul 2022 19:09:16 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org,
        Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 09/25] KVM: VMX: nVMX: Support TSC scaling and
 PERF_GLOBAL_CTRL with enlightened VMCS

On 7/21/22 23:58, Sean Christopherson wrote:
> 
> diff --git a/arch/x86/kvm/vmx/evmcs.c b/arch/x86/kvm/vmx/evmcs.c
> index b5cfbf7d487b..7b348a03e096 100644
> --- a/arch/x86/kvm/vmx/evmcs.c
> +++ b/arch/x86/kvm/vmx/evmcs.c
> @@ -355,11 +355,6 @@ uint16_t nested_get_evmcs_version(struct kvm_vcpu *vcpu)
>          return 0;
>   }
> 
> -enum evmcs_v1_revision {
> -       EVMCSv1_2016,
> -       EVMCSv1_2022,
> -};
> -
>   enum evmcs_unsupported_ctrl_type {
>          EVMCS_EXIT_CTLS,
>          EVMCS_ENTRY_CTLS,
> @@ -372,29 +367,29 @@ static u32 evmcs_get_unsupported_ctls(struct kvm_vcpu *vcpu,
>                                        enum evmcs_unsupported_ctrl_type ctrl_type)
>   {
>          struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
> -       enum evmcs_v1_revision evmcs_rev = EVMCSv1_2016;
> +       bool has_evmcs_2022_features;
> 
>          if (!hv_vcpu)
>                  return 0;
> 
> -       if (hv_vcpu->cpuid_cache.nested_ebx & HV_X64_NESTED_EVMCS1_2022_UPDATE)
> -               evmcs_rev = EVMCSv1_2022;
> +       has_evmcs_2022_features = hv_vcpu->cpuid_cache.nested_ebx &
> +                                 HV_X64_NESTED_EVMCS1_2022_UPDATE;
> 
>          switch (ctrl_type) {
>          case EVMCS_EXIT_CTLS:
> -               if (evmcs_rev == EVMCSv1_2016)
> +               if (!has_evmcs_2022_features)
>                          return EVMCS1_UNSUPPORTED_VMEXIT_CTRL |
>                                  VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL;
>                  else
>                          return EVMCS1_UNSUPPORTED_VMEXIT_CTRL;
>          case EVMCS_ENTRY_CTLS:
> -               if (evmcs_rev == EVMCSv1_2016)
> +               if (!has_evmcs_2022_features)
>                          return EVMCS1_UNSUPPORTED_VMENTRY_CTRL |
>                                  VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL;
>                  else
>                          return EVMCS1_UNSUPPORTED_VMENTRY_CTRL;
>          case EVMCS_2NDEXEC:
> -               if (evmcs_rev == EVMCSv1_2016)
> +               if (!has_evmcs_2022_features)
>                          return EVMCS1_UNSUPPORTED_2NDEXEC |
>                                  SECONDARY_EXEC_TSC_SCALING;
>                  else
> 

I kind of like the idea of having a two-dimensional array based on the 
enums instead of switch statements, so for now I'll keep Vitaly's enums.

Paolo