[PATCH 05/11] KVM: x86: Disallow tsc manipulation for TDX

[Xiaoyao Li]

From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>

The TSC for TDX guest is fixed at TD creation time.

Introduce kvm_tsc_immutable() to tell if TSC is immutable or not.
If immutable, short circuit all paths that lead to one of the myriad TSC
adjustment flows.

Suggested-by: Kai Huang <kai.huang@xxxxxxxxxxxxxxx>
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
---
 arch/x86/kvm/x86.c | 34 ++++++++++++++++++++++++++--------
 arch/x86/kvm/x86.h |  5 +++++
 2 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2b21c5169f32..34dd93b29932 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2247,7 +2247,9 @@ static int set_tsc_khz(struct kvm_vcpu *vcpu, u32 user_tsc_khz, bool scale)
 	u64 ratio;
 
 	/* Guest TSC same frequency as host TSC? */
-	if (!scale) {
+	if (!scale || kvm_tsc_immutable(vcpu)) {
+		if (scale)
+			pr_warn_ratelimited("Guest TSC immutable, scaling not supported\n");
 		kvm_vcpu_write_tsc_multiplier(vcpu, kvm_default_tsc_scaling_ratio);
 		return 0;
 	}
@@ -2534,6 +2536,9 @@ static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 data)
 	bool matched = false;
 	bool synchronizing = false;
 
+	if (WARN_ON_ONCE(kvm_tsc_immutable(vcpu)))
+		return;
+
 	raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
 	offset = kvm_compute_l1_tsc_offset(vcpu, data);
 	ns = get_kvmclock_base_ns();
@@ -2960,6 +2965,10 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
 	u8 pvclock_flags;
 	bool use_master_clock;
 
+	/* Unable to update guest time if the TSC is immutable. */
+	if (kvm_tsc_immutable(v))
+		return 0;
+
 	kernel_ns = 0;
 	host_tsc = 0;
 
@@ -4332,7 +4341,7 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 		if (tsc_delta < 0)
 			mark_tsc_unstable("KVM discovered backwards TSC");
 
-		if (kvm_check_tsc_unstable()) {
+		if (kvm_check_tsc_unstable() && !kvm_tsc_immutable(vcpu)) {
 			u64 offset = kvm_compute_l1_tsc_offset(vcpu,
 						vcpu->arch.last_guest_tsc);
 			kvm_vcpu_write_tsc_offset(vcpu, offset);
@@ -4346,7 +4355,8 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 		 * On a host with synchronized TSC, there is no need to update
 		 * kvmclock on vcpu->cpu migration
 		 */
-		if (!vcpu->kvm->arch.use_master_clock || vcpu->cpu == -1)
+		if ((!vcpu->kvm->arch.use_master_clock || vcpu->cpu == -1) &&
+		    !kvm_tsc_immutable(vcpu))
 			kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu);
 		if (vcpu->cpu != cpu)
 			kvm_make_request(KVM_REQ_MIGRATE_TIMER, vcpu);
@@ -5274,10 +5284,11 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 		break;
 	}
 	case KVM_SET_TSC_KHZ: {
-		u32 user_tsc_khz;
+		u32 user_tsc_khz = (u32)arg;
 
 		r = -EINVAL;
-		user_tsc_khz = (u32)arg;
+		if (kvm_tsc_immutable(vcpu))
+			goto out;
 
 		if (kvm_has_tsc_control &&
 		    user_tsc_khz >= kvm_max_guest_tsc_khz)
@@ -10857,9 +10868,12 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
 
 	if (mutex_lock_killable(&vcpu->mutex))
 		return;
-	vcpu_load(vcpu);
-	kvm_synchronize_tsc(vcpu, 0);
-	vcpu_put(vcpu);
+
+	if (!kvm_tsc_immutable(vcpu)) {
+		vcpu_load(vcpu);
+		kvm_synchronize_tsc(vcpu, 0);
+		vcpu_put(vcpu);
+	}
 
 	/* poll control enabled by default */
 	vcpu->arch.msr_kvm_poll_control = 1;
@@ -11119,6 +11133,10 @@ int kvm_arch_hardware_enable(void)
 	if (backwards_tsc) {
 		u64 delta_cyc = max_tsc - local_tsc;
 		list_for_each_entry(kvm, &vm_list, vm_list) {
+			if (kvm_tsc_immutable(vcpu)) {
+				pr_warn_ratelimited("Backwards TSC observed and guest with immutable TSC active\n");
+				continue;
+			}
 			kvm->arch.backwards_tsc_observed = true;
 			kvm_for_each_vcpu(i, vcpu, kvm) {
 				vcpu->arch.tsc_offset_adjustment += delta_cyc;
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 69c60297bef2..0d8435b32bf5 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -446,6 +446,11 @@ static __always_inline bool kvm_guest_mce_disallowed(struct kvm *kvm)
 	return kvm->arch.vm_type == KVM_X86_TDX_VM;
 }
 
+static __always_inline bool kvm_tsc_immutable(struct kvm_vcpu *vcpu)
+{
+	return vcpu->kvm->arch.vm_type == KVM_X86_TDX_VM;
+}
+
 void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu);
 void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu);
 int kvm_spec_ctrl_test_value(u64 value);
-- 
2.27.0