[v4,3/5] KVM: SVM: Add GUEST_TSC_FREQ MSR for Secure TSC enabled guests

Commit Message

Nikunj A Dadhania March 10, 2025, 6:45 a.m. UTC

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.

Signed-off-by: Nikunj A Dadhania <[e-mail]>
---
 arch/x86/include/asm/svm.h |  1 +
 arch/x86/kvm/svm/sev.c     |  3 +++
 arch/x86/kvm/svm/svm.c     |  1 +
 arch/x86/kvm/svm/svm.h     | 11 ++++++++++-
 4 files changed, 15 insertions(+), 1 deletion(-)

Patch

diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
index 9b7fa99ae951..6ab66b80e751 100644
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -290,6 +290,7 @@  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)
 
 struct vmcb_seg {
 	u16 selector;
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 0bc708ee2788..50263b473f95 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -4504,6 +4504,9 @@  static void sev_es_init_vmcb(struct vcpu_svm *svm)
 	/* Clear intercepts on selected MSRs */
 	set_msr_interception(vcpu, svm->msrpm, MSR_EFER, 1, 1);
 	set_msr_interception(vcpu, svm->msrpm, MSR_IA32_CR_PAT, 1, 1);
+
+	if (snp_secure_tsc_enabled(vcpu->kvm))
+		set_msr_interception(vcpu, svm->msrpm, MSR_AMD64_GUEST_TSC_FREQ, 1, 1);
 }
 
 void sev_init_vmcb(struct vcpu_svm *svm)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 8abeab91d329..e65721db1f81 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -143,6 +143,7 @@  static const struct svm_direct_access_msrs {
 	{ .index = X2APIC_MSR(APIC_TMICT),		.always = false },
 	{ .index = X2APIC_MSR(APIC_TMCCT),		.always = false },
 	{ .index = X2APIC_MSR(APIC_TDCR),		.always = false },
+	{ .index = MSR_AMD64_GUEST_TSC_FREQ,		.always = false },
 	{ .index = MSR_INVALID,				.always = false },
 };
 
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index d4490eaed55d..711e21b7a3d0 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -44,7 +44,7 @@  static inline struct page *__sme_pa_to_page(unsigned long pa)
 #define	IOPM_SIZE PAGE_SIZE * 3
 #define	MSRPM_SIZE PAGE_SIZE * 2
 
-#define MAX_DIRECT_ACCESS_MSRS	48
+#define MAX_DIRECT_ACCESS_MSRS	49
 #define MSRPM_OFFSETS	32
 extern u32 msrpm_offsets[MSRPM_OFFSETS] __read_mostly;
 extern bool npt_enabled;
@@ -377,10 +377,19 @@  static __always_inline bool sev_snp_guest(struct kvm *kvm)
 	return (sev->vmsa_features & SVM_SEV_FEAT_SNP_ACTIVE) &&
 	       !WARN_ON_ONCE(!sev_es_guest(kvm));
 }
+
+static inline bool snp_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));
+}
 #else
 #define sev_guest(kvm) false
 #define sev_es_guest(kvm) false
 #define sev_snp_guest(kvm) false
+#define snp_secure_tsc_enabled(kvm) false
 #endif
 
 static inline bool ghcb_gpa_is_registered(struct vcpu_svm *svm, u64 val)