Re: [PATCH v3 13/15] KVM: nSVM: Use KVM-governed feature framework to track "vGIF enabled"

[Yuan Yao]

On Tue, Aug 15, 2023 at 01:36:51PM -0700, Sean Christopherson wrote:
> Track "virtual GIF exposed to L1" via a governed feature flag instead of
> using a dedicated bit/flag in vcpu_svm.
>
> Note, checking KVM's capabilities instead of the "vgif" param means that
> the code isn't strictly equivalent, as vgif_enabled could have been set
> if nested=false where as that the governed feature cannot.  But that's a
> glorified nop as the feature/flag is consumed only by paths that are

gated by nSVM being enabled.

>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>  arch/x86/kvm/governed_features.h | 1 +
>  arch/x86/kvm/svm/nested.c        | 3 ++-
>  arch/x86/kvm/svm/svm.c           | 3 +--
>  arch/x86/kvm/svm/svm.h           | 5 +++--
>  4 files changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/governed_features.h b/arch/x86/kvm/governed_features.h
> index 9afd34f30599..368696c2e96b 100644
> --- a/arch/x86/kvm/governed_features.h
> +++ b/arch/x86/kvm/governed_features.h
> @@ -14,6 +14,7 @@ KVM_GOVERNED_X86_FEATURE(V_VMSAVE_VMLOAD)
>  KVM_GOVERNED_X86_FEATURE(LBRV)
>  KVM_GOVERNED_X86_FEATURE(PAUSEFILTER)
>  KVM_GOVERNED_X86_FEATURE(PFTHRESHOLD)
> +KVM_GOVERNED_X86_FEATURE(VGIF)
>
>  #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 ac03b2bc5b2c..dd496c9e5f91 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -660,7 +660,8 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm,
>  	 * exit_int_info, exit_int_info_err, next_rip, insn_len, insn_bytes.
>  	 */
>
> -	if (svm->vgif_enabled && (svm->nested.ctl.int_ctl & V_GIF_ENABLE_MASK))
> +	if (guest_can_use(vcpu, X86_FEATURE_VGIF) &&
> +	    (svm->nested.ctl.int_ctl & V_GIF_ENABLE_MASK))
>  		int_ctl_vmcb12_bits |= (V_GIF_MASK | V_GIF_ENABLE_MASK);
>  	else
>  		int_ctl_vmcb01_bits |= (V_GIF_MASK | V_GIF_ENABLE_MASK);
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 9bfff65e8b7a..9eac0ad3403e 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -4302,8 +4302,7 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
>
>  	kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_PAUSEFILTER);
>  	kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_PFTHRESHOLD);
> -
> -	svm->vgif_enabled = vgif && guest_cpuid_has(vcpu, X86_FEATURE_VGIF);
> +	kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_VGIF);
>
>  	svm->vnmi_enabled = vnmi && guest_cpuid_has(vcpu, X86_FEATURE_VNMI);
>
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index d57a096e070a..eaddaac6bf18 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -22,6 +22,7 @@
>  #include <asm/svm.h>
>  #include <asm/sev-common.h>
>
> +#include "cpuid.h"
>  #include "kvm_cache_regs.h"
>
>  #define __sme_page_pa(x) __sme_set(page_to_pfn(x) << PAGE_SHIFT)
> @@ -259,7 +260,6 @@ struct vcpu_svm {
>  	bool soft_int_injected;
>
>  	/* optional nested SVM features that are enabled for this guest  */
> -	bool vgif_enabled                 : 1;
>  	bool vnmi_enabled                 : 1;
>
>  	u32 ldr_reg;
> @@ -443,7 +443,8 @@ static inline bool svm_is_intercept(struct vcpu_svm *svm, int bit)
>
>  static inline bool nested_vgif_enabled(struct vcpu_svm *svm)
>  {
> -	return svm->vgif_enabled && (svm->nested.ctl.int_ctl & V_GIF_ENABLE_MASK);
> +	return guest_can_use(&svm->vcpu, X86_FEATURE_VGIF) &&
> +	       (svm->nested.ctl.int_ctl & V_GIF_ENABLE_MASK);
>  }
>
>  static inline struct vmcb *get_vgif_vmcb(struct vcpu_svm *svm)
> --
> 2.41.0.694.ge786442a9b-goog
>