linux-kernel - Re: [PATCH 08/12] KVM: nSVM: Use KVM-governed feature framework to track "vVM{SAVE,LOAD} enabled"

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Message-ID: <20230221152349.ulcjtbnvziair7ff@linux.intel.com>
Date:   Tue, 21 Feb 2023 23:23:49 +0800
From:   Yu Zhang <yu.c.zhang@...ux.intel.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/12] KVM: nSVM: Use KVM-governed feature framework to
 track "vVM{SAVE,LOAD} enabled"

On Fri, Feb 17, 2023 at 03:10:18PM -0800, Sean Christopherson wrote:
> Track "virtual VMSAVE/VMLOAD 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@...gle.com>
> ---
>  arch/x86/kvm/governed_features.h | 1 +
>  arch/x86/kvm/svm/nested.c        | 2 +-
>  arch/x86/kvm/svm/svm.c           | 5 ++---
>  arch/x86/kvm/svm/svm.h           | 1 -
>  4 files changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/governed_features.h b/arch/x86/kvm/governed_features.h
> index 0335576a80a8..b66b9d550f33 100644
> --- a/arch/x86/kvm/governed_features.h
> +++ b/arch/x86/kvm/governed_features.h
> @@ -9,6 +9,7 @@ KVM_GOVERNED_X86_FEATURE(GBPAGES)
>  KVM_GOVERNED_X86_FEATURE(XSAVES)
>  KVM_GOVERNED_X86_FEATURE(NRIPS)
>  KVM_GOVERNED_X86_FEATURE(TSCRATEMSR)
> +KVM_GOVERNED_X86_FEATURE(V_VMSAVE_VMLOAD)
>  
>  #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 30e00c4e07c7..6a96058c0e48 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -107,7 +107,7 @@ static void nested_svm_uninit_mmu_context(struct kvm_vcpu *vcpu)
>  
>  static bool nested_vmcb_needs_vls_intercept(struct vcpu_svm *svm)
>  {
> -	if (!svm->v_vmload_vmsave_enabled)
> +	if (!guest_can_use(&svm->vcpu, X86_FEATURE_V_VMSAVE_VMLOAD))
>  		return true;
>  
>  	if (!nested_npt_enabled(svm))
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index dd4aead5462c..b3f0271c73b9 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -1162,8 +1162,6 @@ static inline void init_vmcb_after_set_cpuid(struct kvm_vcpu *vcpu)
>  
>  		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_EIP, 0, 0);
>  		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_ESP, 0, 0);
> -
> -		svm->v_vmload_vmsave_enabled = false;
>  	} else {
>  		/*
>  		 * If hardware supports Virtual VMLOAD VMSAVE then enable it
> @@ -4153,7 +4151,8 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
>  
>  	svm->lbrv_enabled = lbrv && guest_cpuid_has(vcpu, X86_FEATURE_LBRV);
>  
> -	svm->v_vmload_vmsave_enabled = vls && guest_cpuid_has(vcpu, X86_FEATURE_V_VMSAVE_VMLOAD);
> +	if (vls && !guest_cpuid_is_intel(vcpu))
> +		kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_V_VMSAVE_VMLOAD);

Sorry, why guest_cpuid_is_intel(vcpu)? Is it becasue that a AMD host with virtual
VMSAVE/VMLOAD capability will always expose this feature for all AMD guests? 

If yes, how about adding some comments? Thanks!

B.R.
Yu