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

From: Maxim Levitsky
Date: Thu Jul 04 2024 - 22:22:42 EST


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