On 9/18/25 05:27, Naveen N Rao (AMD) wrote:
> 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.
A sample command line like in the previous patches would be consistent.
>
> Co-developed-by: Ketan Chaturvedi <ketan.chaturv...@amd.com>
> Signed-off-by: Ketan Chaturvedi <ketan.chaturv...@amd.com>
> Co-developed-by: Nikunj A Dadhania <nik...@amd.com>
> Signed-off-by: Nikunj A Dadhania <nik...@amd.com>
> Signed-off-by: Naveen N Rao (AMD) <nav...@kernel.org>
It would be nice to have a follow-up patch that cleans up
check_sev_features() so that there aren't a bunch of checks with "if
(sev_snp_enabled() ...". Having all the SNP related checks under one "if"
block might be cleaner as more SNP only features get added. Just a thought.
> ---
> target/i386/sev.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
> qapi/qom.json | 6 +++++-
> 2 files changed, 50 insertions(+), 1 deletion(-)
>
> diff --git a/target/i386/sev.c b/target/i386/sev.c
> index 679bedb63c3a..ef54265f4e46 100644
> --- a/target/i386/sev.c
> +++ b/target/i386/sev.c
> @@ -178,6 +178,7 @@ 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;
> @@ -536,6 +537,13 @@ 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;
> }
>
> @@ -1085,6 +1093,18 @@ sev_snp_launch_start(SevCommonState *sev_common)
> return 1;
> }
>
> + if (is_sev_feature_set(sev_common, SVM_SEV_FEAT_SECURE_TSC)) {
> + 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;
> + }
It looks like KVM_CAP_VM_TSC_CONTROL is required for Secure TSC. Should
this cap check be part of check_sev_features() then, rather than waiting
until launch start?
And does KVM_SET_TSC_KHZ have to be called if "tsc-frequency" wasn't set?
Thanks,
Tom
> + }
> +
> rc = sev_ioctl(sev_common->sev_fd, KVM_SEV_SNP_LAUNCH_START,
> start, &fw_error);
> if (rc < 0) {
> @@ -3127,6 +3147,28 @@ 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)
> {
> @@ -3165,6 +3207,9 @@ 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
> diff --git a/qapi/qom.json b/qapi/qom.json
> index 52c23e85e349..c01ae70dd43d 100644
> --- a/qapi/qom.json
> +++ b/qapi/qom.json
> @@ -1103,6 +1103,9 @@
> # @secure-tsc: enable Secure TSC
> # (default: false) (since 10.2)
> #
> +# @tsc-frequency: set secure TSC frequency. Only valid if Secure TSC
> +# is enabled (default: zero) (since 10.2)
> +#
> # Since: 9.1
> ##
> { 'struct': 'SevSnpGuestProperties',
> @@ -1115,7 +1118,8 @@
> '*author-key-enabled': 'bool',
> '*host-data': 'str',
> '*vcek-disabled': 'bool',
> - '*secure-tsc': 'bool' } }
> + '*secure-tsc': 'bool',
> + '*tsc-frequency': 'uint32' } }
>
> ##
> # @TdxGuestProperties:
