Re: [PATCH 2/2] KVM: SEV: Configure "ALLOWED_SEV_FEATURES" VMCB Field

["Nikunj A. Dadhania" <nikunj@amd.com>]

On 8/2/2024 7:27 AM, Kim Phillips wrote:
> From: Kishon Vijay Abraham I <kvijayab@amd.com>
> 
> AMD EPYC 5th generation processors have introduced a feature that allows
> the hypervisor to control the SEV_FEATURES that are set for or by a
> guest [1]. The ALLOWED_SEV_FEATURES feature can be used by the hypervisor
> to enforce that SEV-ES and SEV-SNP guests cannot enable features that the
> hypervisor does not want to be enabled.
> 
> When ALLOWED_SEV_FEATURES is enabled, a VMRUN will fail if any
> non-reserved bits are 1 in SEV_FEATURES but are 0 in
> ALLOWED_SEV_FEATURES.
> 
> [1] Section 15.36.20 "Allowed SEV Features", AMD64 Architecture
>     Programmer's Manual, Pub. 24593 Rev. 3.42 - March 2024:
>     https://bugzilla.kernel.org/attachment.cgi?id=306250
> 
> Signed-off-by: Kishon Vijay Abraham I <kvijayab@amd.com>
> Signed-off-by: Kim Phillips <kim.phillips@amd.com>

Looks good to me.

Reviewed-by: Nikunj A. Dadhania <nikunj@amd.com>

> ---
>  arch/x86/include/asm/svm.h | 6 +++++-
>  arch/x86/kvm/svm/sev.c     | 5 +++++
>  2 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
> index f0dea3750ca9..59516ad2028b 100644
> --- a/arch/x86/include/asm/svm.h
> +++ b/arch/x86/include/asm/svm.h
> @@ -158,7 +158,9 @@ struct __attribute__ ((__packed__)) vmcb_control_area {
>  	u64 avic_physical_id;	/* Offset 0xf8 */
>  	u8 reserved_7[8];
>  	u64 vmsa_pa;		/* Used for an SEV-ES guest */
> -	u8 reserved_8[720];
> +	u8 reserved_8[40];
> +	u64 allowed_sev_features;	/* Offset 0x138 */
> +	u8 reserved_9[672];
>  	/*
>  	 * Offset 0x3e0, 32 bytes reserved
>  	 * for use by hypervisor/software.
> @@ -294,6 +296,8 @@ static_assert((X2AVIC_MAX_PHYSICAL_ID & AVIC_PHYSICAL_MAX_INDEX_MASK) == X2AVIC_
>  	(SVM_SEV_FEAT_RESTRICTED_INJECTION |	\
>  	 SVM_SEV_FEAT_ALTERNATE_INJECTION)
>  
> +#define VMCB_ALLOWED_SEV_FEATURES_VALID		BIT_ULL(63)
> +
>  struct vmcb_seg {
>  	u16 selector;
>  	u16 attrib;
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index a16c873b3232..d12b4d615b32 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -899,6 +899,7 @@ static int sev_es_sync_vmsa(struct vcpu_svm *svm)
>  static int __sev_launch_update_vmsa(struct kvm *kvm, struct kvm_vcpu *vcpu,
>  				    int *error)
>  {
> +	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
>  	struct sev_data_launch_update_vmsa vmsa;
>  	struct vcpu_svm *svm = to_svm(vcpu);
>  	int ret;
> @@ -908,6 +909,10 @@ static int __sev_launch_update_vmsa(struct kvm *kvm, struct kvm_vcpu *vcpu,
>  		return -EINVAL;
>  	}
>  
> +	if (cpu_feature_enabled(X86_FEATURE_ALLOWED_SEV_FEATURES))
> +		svm->vmcb->control.allowed_sev_features = VMCB_ALLOWED_SEV_FEATURES_VALID |
> +							  sev->vmsa_features;
> +
>  	/* Perform some pre-encryption checks against the VMSA */
>  	ret = sev_es_sync_vmsa(svm);
>  	if (ret)