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From: Zachary Amsden on 12 Jul 2010 22:30
When no platform bugs have been detected, no TSC warps have been
detected, and the hardware guarantees to us TSC does not change
rate or stop with P-state or C-state changes, we can consider it reliable.

Signed-off-by: Zachary Amsden <zamsden(a)redhat.com>
---
arch/x86/kvm/x86.c | 10 +++++++++-
1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e73ddf6..b3cc186 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -55,6 +55,7 @@
#include <asm/mce.h>
#include <asm/i387.h>
#include <asm/xcr.h>
+#include <asm/pvclock-abi.h>

#define MAX_IO_MSRS 256
#define CR0_RESERVED_BITS \
@@ -902,6 +903,13 @@ static inline int kvm_tsc_changes_freq(void)
return ret;
}

+static inline int kvm_tsc_reliable(void)
+{
+ return (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
+ boot_cpu_has(X86_FEATURE_NONSTOP_TSC) &&
+ !check_tsc_unstable());
+}
+
static inline u64 nsec_to_cycles(u64 nsec)
{
WARN_ON(preemptible());
@@ -1025,7 +1033,7 @@ static int kvm_write_guest_time(struct kvm_vcpu *v)
vcpu->hv_clock.tsc_timestamp = tsc_timestamp;
vcpu->hv_clock.system_time = kernel_ns + v->kvm->arch.kvmclock_offset;
vcpu->last_kernel_ns = kernel_ns;
- vcpu->hv_clock.flags = 0;
+ vcpu->hv_clock.flags = kvm_tsc_reliable() ? PVCLOCK_TSC_STABLE_BIT : 0;

/*
* The interface expects us to write an even number signaling that the
--
1.7.1

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Prev: [PATCH 16/18] Use getnsboottime in KVM
Next: [PATCH 08/18] Add helper functions for time computation