Re: [PATCH v2 41/49] KVM: x86: Avoid double CPUID lookup when updating MWAIT at runtime

[Maxim Levitsky]

On Fri, 2024-05-17 at 10:39 -0700, Sean Christopherson wrote:
> Move the handling of X86_FEATURE_MWAIT during CPUID runtime updates to
> utilize the lookup done for other CPUID.0x1 features.
> 
> No functional change intended.
> 
> Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>  arch/x86/kvm/cpuid.c | 13 +++++--------
>  1 file changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 8ada1cac8fcb..258c5fce87fc 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -343,6 +343,11 @@ void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu)
>  
>  		cpuid_entry_change(best, X86_FEATURE_APIC,
>  			   vcpu->arch.apic_base & MSR_IA32_APICBASE_ENABLE);
> +
> +		if (!kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT))
> +			cpuid_entry_change(best, X86_FEATURE_MWAIT,
> +					   vcpu->arch.ia32_misc_enable_msr &
> +					   MSR_IA32_MISC_ENABLE_MWAIT);
>  	}
>  
>  	best = kvm_find_cpuid_entry_index(vcpu, 7, 0);
> @@ -358,14 +363,6 @@ void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu)
>  	if (best && (cpuid_entry_has(best, X86_FEATURE_XSAVES) ||
>  		     cpuid_entry_has(best, X86_FEATURE_XSAVEC)))
>  		best->ebx = xstate_required_size(vcpu->arch.xcr0, true);
> -
> -	if (!kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT)) {
> -		best = kvm_find_cpuid_entry(vcpu, 0x1);
> -		if (best)
> -			cpuid_entry_change(best, X86_FEATURE_MWAIT,
> -					   vcpu->arch.ia32_misc_enable_msr &
> -					   MSR_IA32_MISC_ENABLE_MWAIT);
> -	}
>  }
>  EXPORT_SYMBOL_GPL(kvm_update_cpuid_runtime);
>  

Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>

Best regards,
	Maxim Levitsky