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target/i386: SEV: Add support for setting TSC frequency for Secure TSC

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Add support for configuring the TSC frequency when Secure TSC is enabled
in SEV-SNP guests through a new "tsc-frequency" property on SEV-SNP
guest objects, similar to the vCPU-specific property used by regular
guests and TDX. A new property is needed since SEV-SNP guests require
the TSC frequency to be specified during early SNP_LAUNCH_START command
before any vCPUs are created.

The user-provided TSC frequency is set through KVM_SET_TSC_KHZ before
issuing KVM_SEV_SNP_LAUNCH_START.

Attempts to set TSC frequency on both the SEV_SNP object and the cpu
object result in an error from KVM (on the vCPU ioctl), so do not add
separate checks for the same.

Sample command-line:
  -machine q35,confidential-guest-support=sev0 \
  -object sev-snp-guest,id=sev0,cbitpos=51,reduced-phys-bits=1,secure-tsc=on,tsc-frequency=2500000000

Co-developed-by: Ketan Chaturvedi <Ketan.Chaturvedi@amd.com>
Signed-off-by: Ketan Chaturvedi <Ketan.Chaturvedi@amd.com>
Co-developed-by: Nikunj A Dadhania <nikunj@amd.com>
Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
Signed-off-by: Naveen N Rao (AMD) <naveen@kernel.org>
Link: https://lore.kernel.org/r/af688610978f213a456a7753e1d9fe7d3a51e80a.1779281646.git.naveen@kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Naveen N Rao (AMD) 2026-05-20 18:58:01 +05:30 • committed by Paolo Bonzini
parent a26f9b975d
commit f79c89c296
2 changed files with 51 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

6
qapi/qom.json
View file

@ -1116,6 +1116,9 @@
# @secure-tsc: enable Secure TSC
# (default: false) (since 11.1)
#
# @tsc-frequency: set secure TSC frequency. Only valid if Secure TSC
# is enabled (default: zero) (since 11.1)
#
# Since: 9.1
##
{ 'struct': 'SevSnpGuestProperties',
@ -1128,7 +1131,8 @@
'*author-key-enabled': 'bool',
'*host-data': 'str',
'*vcek-disabled': 'bool',
'*secure-tsc': 'bool' } }
'*secure-tsc': 'bool',
'*tsc-frequency': 'uint32' } }
##
# @TdxGuestProperties:

46
target/i386/sev.c
View file

@ -183,6 +183,7 @@ struct SevSnpGuestState {
char *id_auth_base64;
uint8_t *id_auth;
char *host_data;
uint32_t tsc_khz;
struct kvm_sev_snp_launch_start kvm_start_conf;
struct kvm_sev_snp_launch_finish kvm_finish_conf;
@ -547,6 +548,13 @@ static int check_sev_features(SevCommonState *sev_common, uint64_t sev_features,
__func__, sev_features, sev_common->supported_sev_features);
return -1;
}
if (sev_snp_enabled() && SEV_SNP_GUEST(sev_common)->tsc_khz &&
!(sev_features & SVM_SEV_FEAT_SECURE_TSC)) {
error_setg(errp,
"%s: TSC frequency can only be set if Secure TSC is enabled",
__func__);
return -1;
}
return 0;
}
@ -1095,6 +1103,19 @@ sev_snp_launch_start(SevCommonState *sev_common)
return 1;
}
if (is_sev_feature_set(sev_common, SVM_SEV_FEAT_SECURE_TSC) &&
sev_snp_guest->tsc_khz) {
rc = -EINVAL;
if (kvm_check_extension(kvm_state, KVM_CAP_VM_TSC_CONTROL)) {
rc = kvm_vm_ioctl(kvm_state, KVM_SET_TSC_KHZ, sev_snp_guest->tsc_khz);
}
if (rc < 0) {
error_report("%s: Unable to set Secure TSC frequency to %u kHz ret=%d",
__func__, sev_snp_guest->tsc_khz, rc);
return 1;
}
}
rc = sev_ioctl(sev_common->sev_fd, KVM_SEV_SNP_LAUNCH_START,
start, &fw_error);
if (rc < 0) {
@ -3222,6 +3243,28 @@ static void sev_snp_guest_set_secure_tsc(Object *obj, bool value, Error **errp)
sev_set_feature(SEV_COMMON(obj), SVM_SEV_FEAT_SECURE_TSC, value);
}
static void
sev_snp_guest_get_tsc_frequency(Object *obj, Visitor *v, const char *name,
void *opaque, Error **errp)
{
uint32_t value = SEV_SNP_GUEST(obj)->tsc_khz * 1000;
visit_type_uint32(v, name, &value, errp);
}
static void
sev_snp_guest_set_tsc_frequency(Object *obj, Visitor *v, const char *name,
void *opaque, Error **errp)
{
uint32_t value;
if (!visit_type_uint32(v, name, &value, errp)) {
return;
}
SEV_SNP_GUEST(obj)->tsc_khz = value / 1000;
}
static void
sev_snp_guest_class_init(ObjectClass *oc, const void *data)
{
@ -3260,6 +3303,9 @@ sev_snp_guest_class_init(ObjectClass *oc, const void *data)
object_class_property_add_bool(oc, "secure-tsc",
sev_snp_guest_get_secure_tsc,
sev_snp_guest_set_secure_tsc);
object_class_property_add(oc, "tsc-frequency", "uint32",
sev_snp_guest_get_tsc_frequency,
sev_snp_guest_set_tsc_frequency, NULL, NULL);
}
static void