[PATCH v4 5/5] KVM: SVM: Enable Secure TSC for SNP guests

Nikunj A Dadhania
2025-03-10T06:45:55Z

From: Ketan Chaturvedi <Ketan.Chaturvedi@amd.com>

Add support for Secure TSC, allowing userspace to configure the Secure TSC
feature for SNP guests. Use the SNP specification's desired TSC frequency
parameter during the SNP_LAUNCH_START command to set the mean TSC
frequency in KHz for Secure TSC enabled guests. If the frequency is not
specified by the VMM, default to tsc_khz.

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>
---
arch/x86/include/uapi/asm/kvm.h | 3 ++-
arch/x86/kvm/svm/sev.c | 19 +++++++++++++++++++
2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 460306b35a4b..075af0dcee25 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -839,7 +839,8 @@ struct kvm_sev_snp_launch_start {
__u64 policy;
__u8 gosvw[16];
__u16 flags;
- __u8 pad0[6];
+ __u8 pad0[2];
+ __u32 desired_tsc_khz;
__u64 pad1[4];
};

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 50263b473f95..b61d6bd75b37 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2205,6 +2205,20 @@ static int snp_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)

start.gctx_paddr = __psp_pa(sev->snp_context);
start.policy = params.policy;
+
+ if (snp_secure_tsc_enabled(kvm)) {
+ u32 user_tsc_khz = params.desired_tsc_khz;
+
+ /* Use tsc_khz if the VMM has not provided the TSC frequency */
+ if (!user_tsc_khz)
+ user_tsc_khz = tsc_khz;
+
+ start.desired_tsc_khz = user_tsc_khz;
+
+ /* Set the arch default TSC for the VM*/
+ kvm->arch.default_tsc_khz = user_tsc_khz;
+ }
+
memcpy(start.gosvw, params.gosvw, sizeof(params.gosvw));
rc = __sev_issue_cmd(argp->sev_fd, SEV_CMD_SNP_LAUNCH_START, &start, &argp->error);
if (rc) {
@@ -2927,6 +2941,8 @@ void __init sev_set_cpu_caps(void)
if (sev_snp_enabled) {
kvm_cpu_cap_set(X86_FEATURE_SEV_SNP);
kvm_caps.supported_vm_types |= BIT(KVM_X86_SNP_VM);
+
+ kvm_cpu_cap_check_and_set(X86_FEATURE_SNP_SECURE_TSC);
}
}

@@ -3059,6 +3075,9 @@ void __init sev_hardware_setup(void)
sev_supported_vmsa_features = 0;
if (sev_es_debug_swap_enabled)
sev_supported_vmsa_features |= SVM_SEV_FEAT_DEBUG_SWAP;
+
+ if (sev_snp_enabled && cpu_feature_enabled(X86_FEATURE_SNP_SECURE_TSC))
+ sev_supported_vmsa_features |= SVM_SEV_FEAT_SECURE_TSC;
}

void sev_hardware_unsetup(void)
--
2.43.0