1 files changed, 15 insertions, 5 deletions

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index e811d4d1c824..904494b924c1 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -104,12 +104,8 @@ static u64 kvm_sched_clock_read(void)
 
 static inline void kvm_sched_clock_init(bool stable)
 {
-        if (!stable) {
-                pv_ops.time.sched_clock = kvm_clock_read;
+        if (!stable)
                 clear_sched_clock_stable();
-                return;
-        }
-
         kvm_sched_clock_offset = kvm_clock_read();
         pv_ops.time.sched_clock = kvm_sched_clock_read;
 
@@ -355,6 +351,20 @@ void __init kvmclock_init(void)
         machine_ops.crash_shutdown  = kvm_crash_shutdown;
 #endif
         kvm_get_preset_lpj();
+
+        /*
+         * X86_FEATURE_NONSTOP_TSC is TSC runs at constant rate
+         * with P/T states and does not stop in deep C-states.
+         *
+         * Invariant TSC exposed by host means kvmclock is not necessary:
+         * can use TSC as clocksource.
+         *
+         */
+        if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
+            boot_cpu_has(X86_FEATURE_NONSTOP_TSC) &&
+            !check_tsc_unstable())
+                kvm_clock.rating = 299;
+
         clocksource_register_hz(&kvm_clock, NSEC_PER_SEC);
         pv_info.name = "KVM";
 }