[PATCH 4.17 278/324] kvmclock: fix TSC calibration for nested guests

Greg Kroah-Hartman
2018-08-23T09:03:32Z

From: Peng Hao <peng.hao2@zte.com.cn>

[ Upstream commit e10f7805032365cc11c739a97f226ebb48aee042 ]

Inside a nested guest, access to hardware can be slow enough that
tsc_read_refs always return ULLONG_MAX, causing tsc_refine_calibration_work
to be called periodically and the nested guest to spend a lot of time
reading the ACPI timer.

However, if the TSC frequency is available from the pvclock page,
we can just set X86_FEATURE_TSC_KNOWN_FREQ and avoid the recalibration.
'refine' operation.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
[Commit message rewritten. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kernel/kvmclock.c | 1 +
1 file changed, 1 insertion(+)

--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -138,6 +138,7 @@ static unsigned long kvm_get_tsc_khz(voi
src = &hv_clock[cpu].pvti;
tsc_khz = pvclock_tsc_khz(src);
put_cpu();
+ setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
return tsc_khz;
}