[RFC PATCH 1/7] target/i386: SEV: Consolidate SEV feature validation to common init path

Naveen N Rao (AMD)
2025-09-11T11:58:01Z

Currently, check_sev_features() is called in multiple places when
processing IGVM files: both when processing the initial VMSA SEV
features from IGVM, as well as when validating the full contents of the
VMSA. Move this to a single point in sev_common_kvm_init() to simplify
the flow, as well as to re-use this function when VMSA SEV features are
being set without using IGVM files.

Since check_sev_features() relies on SVM_SEV_FEAT_SNP_ACTIVE being set
in VMSA SEV features depending on the guest type, set this flag by
default when creating SEV-SNP guests. When using IGVM files, this field
is anyway over-written so that validation in check_sev_features() is
still relevant.

Finally, add a check to ensure SEV features aren't also set through qemu
cli if using IGVM files.

Signed-off-by: Naveen N Rao (AMD) <naveen@kernel.org>
---
target/i386/sev.c | 30 +++++++++++++++++-------------
1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/target/i386/sev.c b/target/i386/sev.c
index 1057b8ab2c60..243e9493ba8d 100644
--- a/target/i386/sev.c
+++ b/target/i386/sev.c
@@ -586,9 +586,6 @@ static int check_vmsa_supported(SevCommonState *sev_common, hwaddr gpa,
vmsa_check.x87_fcw = 0;
vmsa_check.mxcsr = 0;

- if (check_sev_features(sev_common, vmsa_check.sev_features, errp) < 0) {
- return -1;
- }
vmsa_check.sev_features = 0;

if (!buffer_is_zero(&vmsa_check, sizeof(vmsa_check))) {
@@ -1892,20 +1889,29 @@ static int sev_common_kvm_init(ConfidentialGuestSupport *cgs, Error **errp)
* as SEV_STATE_UNINIT.
*/
if (x86machine->igvm) {
+ if (sev_common->sev_features & ~SVM_SEV_FEAT_SNP_ACTIVE) {
+ error_setg(errp, "%s: SEV features can't be specified when using IGVM files",
+ __func__);
+ return -1;
+ }
if (IGVM_CFG_GET_CLASS(x86machine->igvm)
->process(x86machine->igvm, machine->cgs, true, errp) ==
-1) {
return -1;
}
- /*
- * KVM maintains a bitmask of allowed sev_features. This does not
- * include SVM_SEV_FEAT_SNP_ACTIVE which is set accordingly by KVM
- * itself. Therefore we need to clear this flag.
- */
- args.vmsa_features = sev_common->sev_features &
- ~SVM_SEV_FEAT_SNP_ACTIVE;
}

+ if (check_sev_features(sev_common, sev_common->sev_features, errp) < 0) {
+ return -1;
+ }
+
+ /*
+ * KVM maintains a bitmask of allowed sev_features. This does not
+ * include SVM_SEV_FEAT_SNP_ACTIVE which is set accordingly by KVM
+ * itself. Therefore we need to clear this flag.
+ */
+ args.vmsa_features = sev_common->sev_features & ~SVM_SEV_FEAT_SNP_ACTIVE;
+
ret = sev_ioctl(sev_common->sev_fd, KVM_SEV_INIT2, &args, &fw_error);
break;
}
@@ -2518,9 +2524,6 @@ static int cgs_set_guest_state(hwaddr gpa, uint8_t *ptr, uint64_t len,
__func__);
return -1;
}
- if (check_sev_features(sev_common, sa->sev_features, errp) < 0) {
- return -1;
- }
sev_common->sev_features = sa->sev_features;
}
return 0;
@@ -3127,6 +3130,7 @@ sev_snp_guest_instance_init(Object *obj)

/* default init/start/finish params for kvm */
sev_snp_guest->kvm_start_conf.policy = DEFAULT_SEV_SNP_POLICY;
+ SEV_COMMON(sev_snp_guest)->sev_features |= SVM_SEV_FEAT_SNP_ACTIVE;
}

/* guest info specific to sev-snp */
--
2.50.1