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 18:18:44 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>, 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 Mon, Jul 25, 2022, Paolo Bonzini wrote:
> 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.

I don't have a strong opinion on using a 2d array, but unless I'm missing something,
that's nowhere to be found in this patch.  IMO, having the enums without them
providing any unique value is silly and obfuscates the code.