Re: [RFC PATCH 5/7] target/i386: SEV: Add support for enabling Secure TSC SEV feature

Tom Lendacky
2025-09-12T14:14:44Z

On 9/11/25 06:54, Naveen N Rao (AMD) wrote:
> Add support for enabling Secure TSC VMSA SEV feature in SEV-SNP guests
> through a new "secure-tsc" boolean property on SEV-SNP guest objects.
>
> Sample command-line:
> -machine q35,confidential-guest-support=sev0 \
> -object sev-snp-guest,id=sev0,cbitpos=51,reduced-phys-bits=1,secure-tsc=on
>

Since the next patch talks about setting a TSC value, it would be a good
idea to document the default TSC value that is used when you specify just
this parameter.

Thanks,
Tom

> 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>
> ---
> target/i386/sev.h | 1 +
> target/i386/sev.c | 13 +++++++++++++
> qapi/qom.json | 5 ++++-
> 3 files changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/target/i386/sev.h b/target/i386/sev.h
> index 8e09b2ce1976..87e73034ad15 100644
> --- a/target/i386/sev.h
> +++ b/target/i386/sev.h
> @@ -46,6 +46,7 @@ bool sev_snp_enabled(void);
>
> #define SVM_SEV_FEAT_SNP_ACTIVE BIT(0)
> #define SVM_SEV_FEAT_DEBUG_SWAP BIT(5)
> +#define SVM_SEV_FEAT_SECURE_TSC BIT(9)
>
> typedef struct SevKernelLoaderContext {
> char *setup_data;
> diff --git a/target/i386/sev.c b/target/i386/sev.c
> index 3063ad2d077a..8f88df19a408 100644
> --- a/target/i386/sev.c
> +++ b/target/i386/sev.c
> @@ -3117,6 +3117,16 @@ sev_snp_guest_set_host_data(Object *obj, const char *value, Error **errp)
> memcpy(finish->host_data, blob, len);
> }
>
> +static bool sev_snp_guest_get_secure_tsc(Object *obj, Error **errp)
> +{
> + return is_sev_feature_set(SEV_COMMON(obj), SVM_SEV_FEAT_SECURE_TSC);
> +}
> +
> +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_class_init(ObjectClass *oc, const void *data)
> {
> @@ -3152,6 +3162,9 @@ sev_snp_guest_class_init(ObjectClass *oc, const void *data)
> object_class_property_add_str(oc, "host-data",
> sev_snp_guest_get_host_data,
> sev_snp_guest_set_host_data);
> + object_class_property_add_bool(oc, "secure-tsc",
> + sev_snp_guest_get_secure_tsc,
> + sev_snp_guest_set_secure_tsc);
> }
>
> static void
> diff --git a/qapi/qom.json b/qapi/qom.json
> index 71cd8ad588b5..b05a475ef499 100644
> --- a/qapi/qom.json
> +++ b/qapi/qom.json
> @@ -1100,6 +1100,8 @@
> # firmware. Set this to true to disable the use of VCEK.
> # (default: false) (since: 9.1)
> #
> +# @secure-tsc: enable Secure TSC (default: false) (since 10.2)
> +#
> # Since: 9.1
> ##
> { 'struct': 'SevSnpGuestProperties',
> @@ -1111,7 +1113,8 @@
> '*id-auth': 'str',
> '*author-key-enabled': 'bool',
> '*host-data': 'str',
> - '*vcek-disabled': 'bool' } }
> + '*vcek-disabled': 'bool',
> + '*secure-tsc': 'bool' } }
>
> ##