Re: [RFC PATCH v3 06/27] KVM: SVM: Add helper to check if Secure AVIC is enabled for a guest

[Tom Lendacky <thomas.lendacky@amd.com>]

On 7/8/26 01:32, Naveen N Rao (AMD) wrote:
> Add a helper snp_is_secure_avic_enabled() along the lines of the similar
> helper for Secure TSC to check if Secure AVIC is enabled in the VMSA SEV
> Features for a SEV-SNP guest.
> 
> Note: Enabling Secure AVIC in the VMSA SEV Features puts the SEV-SNP
> guest in Secure AVIC "mode", and it is up to the guest to then "enable"
> Secure AVIC through the Secure AVIC Control MSR. While the use of
> "enabled" in the helper might sound like a misnomer, it reflects the
> fact that KVM has no visibility into whether the guest has actually
> enabled Secure AVIC or not. For all practical purposes, KVM assumes that
> the guest has Secure AVIC enabled. Since a Secure AVIC mode guest is
> extremely restricted, it is in the best interest of the guest to enable
> Secure AVIC at the earliest.

The last sentence probably isn't needed.

And typically the function isn't introduced until it is used. But if no
one has any objection:

Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>

> 
> Signed-off-by: Naveen N Rao (AMD) <naveen@kernel.org>
> ---
>  arch/x86/include/asm/svm.h | 1 +
>  arch/x86/kvm/svm/svm.h     | 2 ++
>  arch/x86/kvm/svm/sev.c     | 8 ++++++++
>  3 files changed, 11 insertions(+)
> 
> diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
> index 42ececa8963d..5857b942957b 100644
> --- a/arch/x86/include/asm/svm.h
> +++ b/arch/x86/include/asm/svm.h
> @@ -311,6 +311,7 @@ static_assert((X2AVIC_4K_MAX_PHYSICAL_ID & AVIC_PHYSICAL_MAX_INDEX_MASK) == X2AV
>  #define SVM_SEV_FEAT_ALTERNATE_INJECTION		BIT(4)
>  #define SVM_SEV_FEAT_DEBUG_SWAP				BIT(5)
>  #define SVM_SEV_FEAT_SECURE_TSC				BIT(9)
> +#define SVM_SEV_FEAT_SECURE_AVIC			BIT(16)
>  
>  #define VMCB_ALLOWED_SEV_FEATURES_VALID			BIT_ULL(63)
>  
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 616e45624f4c..1157d022bac1 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -1013,6 +1013,7 @@ void sev_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end);
>  int sev_gmem_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn, bool is_private);
>  struct vmcb_save_area *sev_decrypt_vmsa(struct kvm_vcpu *vcpu);
>  void sev_free_decrypted_vmsa(struct kvm_vcpu *vcpu, struct vmcb_save_area *vmsa);
> +bool snp_is_secure_avic_enabled(struct kvm *kvm);
>  #else
>  static inline struct page *snp_safe_alloc_page_node(int node, gfp_t gfp)
>  {
> @@ -1050,6 +1051,7 @@ static inline struct vmcb_save_area *sev_decrypt_vmsa(struct kvm_vcpu *vcpu)
>  	return NULL;
>  }
>  static inline void sev_free_decrypted_vmsa(struct kvm_vcpu *vcpu, struct vmcb_save_area *vmsa) {}
> +static inline bool snp_is_secure_avic_enabled(struct kvm *kvm) { return false; }
>  #endif
>  
>  /* vmenter.S */
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 74fb15551e83..686227a15328 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -211,6 +211,14 @@ static bool snp_is_secure_tsc_enabled(struct kvm *kvm)
>  	       !WARN_ON_ONCE(!sev_snp_guest(kvm));
>  }
>  
> +bool snp_is_secure_avic_enabled(struct kvm *kvm)
> +{
> +	struct kvm_sev_info *sev = to_kvm_sev_info(kvm);
> +
> +	return (sev->vmsa_features & SVM_SEV_FEAT_SECURE_AVIC) &&
> +	       !WARN_ON_ONCE(!sev_snp_guest(kvm));
> +}
> +
>  /* Must be called with the sev_bitmap_lock held */
>  static bool __sev_recycle_asids(unsigned int min_asid, unsigned int max_asid)
>  {