[KVM timekeeping 33/35] Indicate reliable TSC in kvmclock

[Zachary Amsden]

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@xxxxxxxxxx>
---
 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 86f182a..a7fa24e 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						\
@@ -900,6 +901,13 @@ static void kvm_get_time_scale(uint32_t scaled_khz, uint32_t base_khz,
 static DEFINE_PER_CPU(unsigned long, cpu_tsc_khz);
 unsigned long max_tsc_khz;
 
+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(struct kvm *kvm, u64 nsec)
 {
 	return pvclock_scale_delta(nsec, kvm->arch.virtual_tsc_mult,
@@ -1151,7 +1159,7 @@ static int kvm_guest_time_update(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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