On 2/7/25 17:34, Kim Phillips wrote: > 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]. ALLOWED_SEV_FEATURES 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. > > Some SEV_FEATURES - currently PmcVirtualization and SecureAvic > (see Appendix B, Table B-4) - require an opt-in via ALLOWED_SEV_FEATURES, > i.e. are off-by-default, whereas all other features are effectively > on-by-default, but still honor 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 > > Co-developed-by: Kishon Vijay Abraham I <kvijayab@xxxxxxx> > Signed-off-by: Kishon Vijay Abraham I <kvijayab@xxxxxxx> > Signed-off-by: Kim Phillips <kim.phillips@xxxxxxx> > --- > arch/x86/include/asm/svm.h | 5 ++++- > arch/x86/kvm/svm/sev.c | 17 +++++++++++++++++ > 2 files changed, 21 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h > index e2fac21471f5..6d94a727cc1a 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. > @@ -289,6 +291,7 @@ static_assert((X2AVIC_MAX_PHYSICAL_ID & AVIC_PHYSICAL_MAX_INDEX_MASK) == X2AVIC_ > #define SVM_SEV_FEAT_RESTRICTED_INJECTION BIT(3) > #define SVM_SEV_FEAT_ALTERNATE_INJECTION BIT(4) > #define SVM_SEV_FEAT_DEBUG_SWAP BIT(5) > +#define SVM_SEV_FEAT_ALLOWED_SEV_FEATURES BIT_ULL(63) Hmmm... I believe it is safe to define this bit value, as the Allowed SEV features VMCB field shows bits 61:0 being used for the allowed features mask and we know that the SEV_FEATURES field is used in the SEV Features MSR left-shifted 2 bits, so we only expect bits 61:0 to be used and bits 62 and 63 will always be reserved. But, given that I think we need two functions: - get_allowed_sev_features() keeping it as you have it below, where it returns the sev->vmsa_features bitmap if SVM_SEV_FEAT_ALLOWED_SEV_FEATURES is set or 0 if SVM_SEV_FEAT_ALLOWED_SEV_FEATURES is not set. - get_vmsa_sev_features() which removes the SVM_SEV_FEAT_ALLOWED_SEV_FEATURES bit, since it is not defined in the VMSA SEV_FEATURES definition. > > #define SVM_SEV_FEAT_INT_INJ_MODES \ > (SVM_SEV_FEAT_RESTRICTED_INJECTION | \ > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c > index a2a794c32050..a9e16792cac0 100644 > --- a/arch/x86/kvm/svm/sev.c > +++ b/arch/x86/kvm/svm/sev.c > @@ -894,9 +894,19 @@ static int sev_es_sync_vmsa(struct vcpu_svm *svm) > return 0; > } > > +static u64 allowed_sev_features(struct kvm_sev_info *sev) > +{ > + if (cpu_feature_enabled(X86_FEATURE_ALLOWED_SEV_FEATURES) && Not sure if the cpu_feature_enabled() check is necessary, as init should have failed if SVM_SEV_FEAT_ALLOWED_SEV_FEATURES wasn't set in sev_supported_vmsa_features. Thanks, Tom > + (sev->vmsa_features & SVM_SEV_FEAT_ALLOWED_SEV_FEATURES)) > + return sev->vmsa_features; > + > + return 0; > +} > + > 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; > @@ -906,6 +916,8 @@ static int __sev_launch_update_vmsa(struct kvm *kvm, struct kvm_vcpu *vcpu, > return -EINVAL; > } > > + svm->vmcb->control.allowed_sev_features = allowed_sev_features(sev); > + > /* Perform some pre-encryption checks against the VMSA */ > ret = sev_es_sync_vmsa(svm); > if (ret) > @@ -2447,6 +2459,8 @@ static int snp_launch_update_vmsa(struct kvm *kvm, struct kvm_sev_cmd *argp) > struct vcpu_svm *svm = to_svm(vcpu); > u64 pfn = __pa(svm->sev_es.vmsa) >> PAGE_SHIFT; > > + svm->vmcb->control.allowed_sev_features = allowed_sev_features(sev); > + > ret = sev_es_sync_vmsa(svm); > if (ret) > return ret; > @@ -3069,6 +3083,9 @@ void __init sev_hardware_setup(void) > sev_supported_vmsa_features = 0; > if (sev_es_debug_swap_enabled) > sev_supported_vmsa_features |= SVM_SEV_FEAT_DEBUG_SWAP; > + > + if (sev_es_enabled && cpu_feature_enabled(X86_FEATURE_ALLOWED_SEV_FEATURES)) > + sev_supported_vmsa_features |= SVM_SEV_FEAT_ALLOWED_SEV_FEATURES; > } > > void sev_hardware_unsetup(void)
