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Subject[patch 8/7] x86/kvmclock: Avoid TSC recalibration

If the host gives us a TSC rate, assume it is good and don't try and
recalibrate things against virtual timer hardware.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -140,7 +140,16 @@ static inline void kvm_sched_clock_init(
*/
static unsigned long kvm_get_tsc_khz(void)
{
- return pvclock_tsc_khz(this_cpu_pvti());
+ unsigned long tsc_khz = pvclock_tsc_khz(this_cpu_pvti());
+
+ /*
+ * TSC frequency is reported by the host; calibration against (virtual)
+ * HPET/PM-timer in a guest is dodgy and pointless since the host already
+ * did it for us where required.
+ */
+ setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
+
+ return tsc_khz;
}

static void kvm_get_preset_lpj(void)
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