"Naveen N Rao (AMD)" <[email protected]> writes: > Add support for enabling debug-swap VMSA SEV feature in SEV-ES and > SEV-SNP guests through a new "debug-swap" boolean property on SEV guest > objects. Though the boolean property is available for plain SEV guests, > check_sev_features() has a check that rejects attempts to enable any SEV > feature for a plain SEV guest.
Why does it make sense to add the property to objects where it's not supported? > Though this SEV feature is called "Debug virtualization" in the APM, KVM > calls this "debug swap" so use the same name for consistency. Thanks for explaining this. > Sample command-line: > -machine q35,confidential-guest-support=sev0 \ > -object sev-snp-guest,id=sev0,cbitpos=51,reduced-phys-bits=1,debug-swap=on > > Restrict debug-swap to SEV-SNP guests at this time due to a > compatibility issue with SEV-ES pflash devices. What are these issues? > Signed-off-by: Naveen N Rao (AMD) <[email protected]> > --- > target/i386/sev.h | 1 + > target/i386/sev.c | 26 ++++++++++++++++++++++++++ > qapi/qom.json | 7 ++++++- > 3 files changed, 33 insertions(+), 1 deletion(-) > > diff --git a/target/i386/sev.h b/target/i386/sev.h > index b84ca3ce0b67..d19a39669747 100644 > --- a/target/i386/sev.h > +++ b/target/i386/sev.h > @@ -47,6 +47,7 @@ bool sev_snp_enabled(void); > #define SEV_SNP_POLICY_DBG 0x80000 > > #define SVM_SEV_FEAT_SNP_ACTIVE BIT(0) > +#define SVM_SEV_FEAT_DEBUG_SWAP BIT(5) > > typedef struct SevKernelLoaderContext { > char *setup_data; > diff --git a/target/i386/sev.c b/target/i386/sev.c > index 4553fe4d6e4a..4532b1b6a484 100644 > --- a/target/i386/sev.c > +++ b/target/i386/sev.c > @@ -328,6 +328,11 @@ sev_set_guest_state(SevCommonState *sev_common, SevState > new_state) > sev_common->state = new_state; > } > > +static bool is_sev_feature_set(SevCommonState *sev_common, uint64_t feature) > +{ > + return !!(sev_common->sev_features & feature); > +} > + > static void sev_set_feature(SevCommonState *sev_common, uint64_t feature, > bool set) > { > if (set) { > @@ -527,6 +532,12 @@ static int check_sev_features(SevCommonState > *sev_common, uint64_t sev_features, > __func__); > return -1; > } > + if (sev_features && sev_es_enabled() && !sev_snp_enabled()) { > + error_setg(errp, > + "%s: SEV features are not supported with SEV-ES at this > time", > + __func__); Once again, I'm confused about SEV. Remind me: what kinds of SEV guests exist? The commit message suggests "plain", "ES", "SNP". What do sev_es_enabled() and sev_snp_enabled() return for each of these? What are the "SEV features"? Can we expect users to know? I suspect they need to know to fix the problem! Are they exactly debug-swap? __func__ in an error message meant for users is an anti-pattern. Not an objection to this patch; it matches existing errors around here. > + return -1; > + } > if (sev_features && !sev_es_enabled()) { > error_setg(errp, > "%s: SEV features require either SEV-ES or SEV-SNP to be > enabled", > @@ -2800,6 +2811,16 @@ static int > cgs_set_guest_policy(ConfidentialGuestPolicyType policy_type, > return 0; > } > > +static bool sev_common_get_debug_swap(Object *obj, Error **errp) > +{ > + return is_sev_feature_set(SEV_COMMON(obj), SVM_SEV_FEAT_DEBUG_SWAP); > +} > + > +static void sev_common_set_debug_swap(Object *obj, bool value, Error **errp) > +{ > + sev_set_feature(SEV_COMMON(obj), SVM_SEV_FEAT_DEBUG_SWAP, value); > +} > + > static void > sev_common_class_init(ObjectClass *oc, const void *data) > { > @@ -2825,6 +2846,11 @@ sev_common_class_init(ObjectClass *oc, const void > *data) > sev_common_set_kernel_hashes); > object_class_property_set_description(oc, "kernel-hashes", > "add kernel hashes to guest firmware for measured Linux boot"); > + object_class_property_add_bool(oc, "debug-swap", > + sev_common_get_debug_swap, > + sev_common_set_debug_swap); > + object_class_property_set_description(oc, "debug-swap", > + "enable virtualization of debug registers"); > } > > static void > diff --git a/qapi/qom.json b/qapi/qom.json > index dd45ac1087c3..e2bb716b603e 100644 > --- a/qapi/qom.json > +++ b/qapi/qom.json > @@ -1017,6 +1017,10 @@ > # designated guest firmware page for measured boot with -kernel > # (default: false) (since 6.2) > # > +# @debug-swap: enable virtualization of debug registers, > +# only supported on SEV-ES and SEV-SNP guests > +# (default: false) (since 11.1) > +# > # Features: > # > # @confidential-guest-reset: If present, the hypervisor supports > @@ -1028,7 +1032,8 @@ > 'data': { '*sev-device': 'str', > '*cbitpos': 'uint32', > 'reduced-phys-bits': 'uint32', > - '*kernel-hashes': 'bool' }, > + '*kernel-hashes': 'bool', > + '*debug-swap': 'bool' }, > 'features': ['confidential-guest-reset']} > > ## This is SevCommonProperties, the common base type of SevGuestProperties (configuration for sev-guest QOM objects) and SevSnpGuestProperties (sev-snp-guest objects). So, all SEV objects have property @debug-swap. I figure the check you add to check_sev_features() rejects it for certain SEV objects. I don't quite understand for which ones.
