Re: [PATCH v3 08/15] KVM: nSVM: Use KVM-governed feature framework to track "NRIPS enabled"

[Yuan Yao]

On Tue, Aug 15, 2023 at 01:36:46PM -0700, Sean Christopherson wrote:
> Track "NRIPS exposed to L1" via a governed feature flag instead of using
> a dedicated bit/flag in vcpu_svm.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

Reviewed-by: Yuan Yao <yuan.yao@xxxxxxxxx>

> ---
>  arch/x86/kvm/governed_features.h | 1 +
>  arch/x86/kvm/svm/nested.c        | 6 +++---
>  arch/x86/kvm/svm/svm.c           | 4 +---
>  arch/x86/kvm/svm/svm.h           | 1 -
>  4 files changed, 5 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/governed_features.h b/arch/x86/kvm/governed_features.h
> index 22446614bf49..722b66af412c 100644
> --- a/arch/x86/kvm/governed_features.h
> +++ b/arch/x86/kvm/governed_features.h
> @@ -8,6 +8,7 @@ BUILD_BUG()
>  KVM_GOVERNED_X86_FEATURE(GBPAGES)
>  KVM_GOVERNED_X86_FEATURE(XSAVES)
>  KVM_GOVERNED_X86_FEATURE(VMX)
> +KVM_GOVERNED_X86_FEATURE(NRIPS)
>
>  #undef KVM_GOVERNED_X86_FEATURE
>  #undef KVM_GOVERNED_FEATURE
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 3342cc4a5189..9092f3f8dccf 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -716,7 +716,7 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm,
>  	 * what a nrips=0 CPU would do (L1 is responsible for advancing RIP
>  	 * prior to injecting the event).
>  	 */
> -	if (svm->nrips_enabled)
> +	if (guest_can_use(vcpu, X86_FEATURE_NRIPS))
>  		vmcb02->control.next_rip    = svm->nested.ctl.next_rip;
>  	else if (boot_cpu_has(X86_FEATURE_NRIPS))
>  		vmcb02->control.next_rip    = vmcb12_rip;
> @@ -726,7 +726,7 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm,
>  		svm->soft_int_injected = true;
>  		svm->soft_int_csbase = vmcb12_csbase;
>  		svm->soft_int_old_rip = vmcb12_rip;
> -		if (svm->nrips_enabled)
> +		if (guest_can_use(vcpu, X86_FEATURE_NRIPS))
>  			svm->soft_int_next_rip = svm->nested.ctl.next_rip;
>  		else
>  			svm->soft_int_next_rip = vmcb12_rip;
> @@ -1026,7 +1026,7 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
>  	if (vmcb12->control.exit_code != SVM_EXIT_ERR)
>  		nested_save_pending_event_to_vmcb12(svm, vmcb12);
>
> -	if (svm->nrips_enabled)
> +	if (guest_can_use(vcpu, X86_FEATURE_NRIPS))
>  		vmcb12->control.next_rip  = vmcb02->control.next_rip;
>
>  	vmcb12->control.int_ctl           = svm->nested.ctl.int_ctl;
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index d67f6e23dcd2..c8b97cb3138c 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -4288,9 +4288,7 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
>  	    guest_cpuid_has(vcpu, X86_FEATURE_XSAVE))
>  		kvm_governed_feature_set(vcpu, X86_FEATURE_XSAVES);
>
> -	/* Update nrips enabled cache */
> -	svm->nrips_enabled = kvm_cpu_cap_has(X86_FEATURE_NRIPS) &&
> -			     guest_cpuid_has(vcpu, X86_FEATURE_NRIPS);
> +	kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_NRIPS);
>
>  	svm->tsc_scaling_enabled = tsc_scaling && guest_cpuid_has(vcpu, X86_FEATURE_TSCRATEMSR);
>  	svm->lbrv_enabled = lbrv && guest_cpuid_has(vcpu, X86_FEATURE_LBRV);
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 5115b35a4d31..e147f2046ffa 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -259,7 +259,6 @@ struct vcpu_svm {
>  	bool soft_int_injected;
>
>  	/* optional nested SVM features that are enabled for this guest  */
> -	bool nrips_enabled                : 1;
>  	bool tsc_scaling_enabled          : 1;
>  	bool v_vmload_vmsave_enabled      : 1;
>  	bool lbrv_enabled                 : 1;
> --
> 2.41.0.694.ge786442a9b-goog
>