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

Nikunj A Dadhania
2025-03-10T06:45:48Z

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 <nikunj@amd.com>
---
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(-)

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)
--
2.43.0