diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9396b3f2c5943581c5d9ac7e72f2f9f64cd7ffa7..4bcb120cc76adcff7c453117e73c6338276496bb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -893,6 +893,16 @@ static void kvm_set_time_scale(uint32_t tsc_khz, struct pvclock_vcpu_time_info *
 		 hv_clock->tsc_to_system_mul);
 }
 
+static inline u64 get_kernel_ns(void)
+{
+	struct timespec ts;
+
+	WARN_ON(preemptible());
+	ktime_get_ts(&ts);
+	monotonic_to_bootbased(&ts);
+	return timespec_to_ns(&ts);
+}
+
 static DEFINE_PER_CPU(unsigned long, cpu_tsc_khz);
 
 static inline int kvm_tsc_changes_freq(void)
@@ -904,18 +914,24 @@ static inline int kvm_tsc_changes_freq(void)
 	return ret;
 }
 
+static inline u64 nsec_to_cycles(u64 nsec)
+{
+	WARN_ON(preemptible());
+	if (kvm_tsc_changes_freq())
+		printk_once(KERN_WARNING
+		 "kvm: unreliable cycle conversion on adjustable rate TSC\n");
+	return (nsec * __get_cpu_var(cpu_tsc_khz)) / USEC_PER_SEC;
+}
+
 void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data)
 {
 	struct kvm *kvm = vcpu->kvm;
 	u64 offset, ns, elapsed;
 	unsigned long flags;
-	struct timespec ts;
 
 	spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
 	offset = data - native_read_tsc();
-	ktime_get_ts(&ts);
-	monotonic_to_bootbased(&ts);
-	ns = timespec_to_ns(&ts);
+	ns = get_kernel_ns();
 	elapsed = ns - kvm->arch.last_tsc_nsec;
 
 	/*
@@ -931,10 +947,9 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data)
 			offset = kvm->arch.last_tsc_offset;
 			pr_debug("kvm: matched tsc offset for %llu\n", data);
 		} else {
-			u64 tsc_delta = elapsed * __get_cpu_var(cpu_tsc_khz);
-			tsc_delta = tsc_delta / USEC_PER_SEC;
-			offset += tsc_delta;
-			pr_debug("kvm: adjusted tsc offset by %llu\n", tsc_delta);
+			u64 delta = nsec_to_cycles(elapsed);
+			offset += delta;
+			pr_debug("kvm: adjusted tsc offset by %llu\n", delta);
 		}
 		ns = kvm->arch.last_tsc_nsec;
 	}
@@ -951,11 +966,11 @@ EXPORT_SYMBOL_GPL(kvm_write_tsc);
 
 static int kvm_write_guest_time(struct kvm_vcpu *v)
 {
-	struct timespec ts;
 	unsigned long flags;
 	struct kvm_vcpu_arch *vcpu = &v->arch;
 	void *shared_kaddr;
 	unsigned long this_tsc_khz;
+	s64 kernel_ns;
 
 	if ((!vcpu->time_page))
 		return 0;
@@ -963,8 +978,7 @@ static int kvm_write_guest_time(struct kvm_vcpu *v)
 	/* Keep irq disabled to prevent changes to the clock */
 	local_irq_save(flags);
 	kvm_get_msr(v, MSR_IA32_TSC, &vcpu->hv_clock.tsc_timestamp);
-	ktime_get_ts(&ts);
-	monotonic_to_bootbased(&ts);
+	kernel_ns = get_kernel_ns();
 	this_tsc_khz = __get_cpu_var(cpu_tsc_khz);
 	local_irq_restore(flags);
 
@@ -979,9 +993,7 @@ static int kvm_write_guest_time(struct kvm_vcpu *v)
 	}
 
 	/* With all the info we got, fill in the values */
-	vcpu->hv_clock.system_time = ts.tv_nsec +
-				     (NSEC_PER_SEC * (u64)ts.tv_sec) + v->kvm->arch.kvmclock_offset;
-
+	vcpu->hv_clock.system_time = kernel_ns + v->kvm->arch.kvmclock_offset;
 	vcpu->hv_clock.flags = 0;
 
 	/*
@@ -3263,7 +3275,6 @@ long kvm_arch_vm_ioctl(struct file *filp,
 		break;
 	}
 	case KVM_SET_CLOCK: {
-		struct timespec now;
 		struct kvm_clock_data user_ns;
 		u64 now_ns;
 		s64 delta;
@@ -3277,19 +3288,16 @@ long kvm_arch_vm_ioctl(struct file *filp,
 			goto out;
 
 		r = 0;
-		ktime_get_ts(&now);
-		now_ns = timespec_to_ns(&now);
+		now_ns = get_kernel_ns();
 		delta = user_ns.clock - now_ns;
 		kvm->arch.kvmclock_offset = delta;
 		break;
 	}
 	case KVM_GET_CLOCK: {
-		struct timespec now;
 		struct kvm_clock_data user_ns;
 		u64 now_ns;
 
-		ktime_get_ts(&now);
-		now_ns = timespec_to_ns(&now);
+		now_ns = get_kernel_ns();
 		user_ns.clock = kvm->arch.kvmclock_offset + now_ns;
 		user_ns.flags = 0;