linux-kernel - [PATCH v11 8/8] KVM: SVM: Enable Secure TSC for SNP guests

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Message-ID: <20250819234833.3080255-9-seanjc@google.com>
Date: Tue, 19 Aug 2025 16:48:33 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Thomas Lendacky <thomas.lendacky@....com>, Michael Roth <michael.roth@....com>, 
	Nikunj A Dadhania <nikunj@....com>, Borislav Petkov <bp@...en8.de>, 
	Vaishali Thakkar <vaishali.thakkar@...e.com>, Ketan Chaturvedi <Ketan.Chaturvedi@....com>, 
	Kai Huang <kai.huang@...el.com>
Subject: [PATCH v11 8/8] KVM: SVM: Enable Secure TSC for SNP guests

From: Nikunj A Dadhania <nikunj@....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.

Always use kvm->arch.arch.default_tsc_khz as the TSC frequency that is
passed to SNP guests in the SNP_LAUNCH_START command.  The default value
is the host TSC frequency.  The userspace can optionally change the TSC
frequency via the KVM_SET_TSC_KHZ ioctl before calling the
SNP_LAUNCH_START ioctl.

Introduce the read-only MSR GUEST_TSC_FREQ (0xc0010134) that returns
guest's effective frequency in MHZ when Secure TSC is enabled for SNP
guests. Disable interception of this MSR when Secure TSC is enabled. Note
that GUEST_TSC_FREQ MSR is accessible only to the guest and not from the
hypervisor context.

Co-developed-by: Ketan Chaturvedi <Ketan.Chaturvedi@....com>
Signed-off-by: Ketan Chaturvedi <Ketan.Chaturvedi@....com>
Reviewed-by: Kai Huang <kai.huang@...el.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
Signed-off-by: Nikunj A Dadhania <nikunj@....com>
[sean: contain Secure TSC to sev.c]
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/include/asm/svm.h |  1 +
 arch/x86/kvm/svm/sev.c     | 26 ++++++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
index ffc27f676243..17f6c3fedeee 100644
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -299,6 +299,7 @@ static_assert((X2AVIC_MAX_PHYSICAL_ID & AVIC_PHYSICAL_MAX_INDEX_MASK) == X2AVIC_
 #define SVM_SEV_FEAT_RESTRICTED_INJECTION		BIT(3)
 #define SVM_SEV_FEAT_ALTERNATE_INJECTION		BIT(4)
 #define SVM_SEV_FEAT_DEBUG_SWAP				BIT(5)
+#define SVM_SEV_FEAT_SECURE_TSC				BIT(9)
 
 #define VMCB_ALLOWED_SEV_FEATURES_VALID			BIT_ULL(63)
 
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 7d1d34e45310..fb45a96e0159 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -146,6 +146,14 @@ static bool sev_vcpu_has_debug_swap(struct vcpu_svm *svm)
 	return sev->vmsa_features & SVM_SEV_FEAT_DEBUG_SWAP;
 }
 
+static bool snp_is_secure_tsc_enabled(struct kvm *kvm)
+{
+	struct kvm_sev_info *sev = to_kvm_sev_info(kvm);
+
+	return (sev->vmsa_features & SVM_SEV_FEAT_SECURE_TSC) &&
+	       !WARN_ON_ONCE(!sev_snp_guest(kvm));
+}
+
 /* Must be called with the sev_bitmap_lock held */
 static bool __sev_recycle_asids(unsigned int min_asid, unsigned int max_asid)
 {
@@ -415,6 +423,9 @@ static int __sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp,
 	if (data->flags)
 		return -EINVAL;
 
+	if (!snp_active)
+		valid_vmsa_features &= ~SVM_SEV_FEAT_SECURE_TSC;
+
 	if (data->vmsa_features & ~valid_vmsa_features)
 		return -EINVAL;
 
@@ -2195,6 +2206,12 @@ 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_is_secure_tsc_enabled(kvm)) {
+		WARN_ON_ONCE(!kvm->arch.default_tsc_khz);
+		start.desired_tsc_khz = kvm->arch.default_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) {
@@ -3085,6 +3102,9 @@ 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 && tsc_khz && cpu_feature_enabled(X86_FEATURE_SNP_SECURE_TSC))
+		sev_supported_vmsa_features |= SVM_SEV_FEAT_SECURE_TSC;
 }
 
 void sev_hardware_unsetup(void)
@@ -4452,6 +4472,9 @@ void sev_es_recalc_msr_intercepts(struct kvm_vcpu *vcpu)
 					  !guest_cpu_cap_has(vcpu, X86_FEATURE_RDTSCP) &&
 					  !guest_cpu_cap_has(vcpu, X86_FEATURE_RDPID));
 
+	svm_set_intercept_for_msr(vcpu, MSR_AMD64_GUEST_TSC_FREQ, MSR_TYPE_R,
+				  !snp_is_secure_tsc_enabled(vcpu->kvm));
+
 	/*
 	 * For SEV-ES, accesses to MSR_IA32_XSS should not be intercepted if
 	 * the host/guest supports its use.
@@ -4591,6 +4614,9 @@ int sev_vcpu_create(struct kvm_vcpu *vcpu)
 		return -ENOMEM;
 
 	svm->sev_es.vmsa = page_address(vmsa_page);
+
+	vcpu->arch.guest_tsc_protected = snp_is_secure_tsc_enabled(vcpu->kvm);
+
 	return 0;
 }
 
-- 
2.51.0.rc1.167.g924127e9c0-goog