Start a new TSC synchronization generation whenever the
IA32_TIME_STAMP_COUNTER MSR is written on a vCPU that has already
participated in the current TSC synchronization generation.
Previously, it was not possible to restore the IA32_TIME_STAMP_COUNTER
MSR to a value less than the TSC frequency. Since vCPU initialization
sets the IA32_TIME_STAMP_COUNTER MSR to zero, a subsequent
KVM_SET_MSRS ioctl that attempted to write a small value to the
IA32_TIME_STAMP_COUNTER MSR was viewed as an attempt at TSC
synchronization. Notably, this was the case even for single vCPU VMs,
which were always synchronized.
Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
Reviewed-by: Peter Shier <pshier@xxxxxxxxxx>
Reviewed-by: Oliver Upton <oupton@xxxxxxxxxx>
---
arch/x86/kvm/x86.c | 13 +++++--------
1 file changed, 5 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9e41b5135340..2555ea2cd91e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2015,7 +2015,6 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr)
u64 offset, ns, elapsed;
unsigned long flags;
bool matched;
- bool already_matched;
u64 data = msr->data;
bool synchronizing = false;
@@ -2032,7 +2031,8 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr)
* kvm_clock stable after CPU hotplug
*/
synchronizing = true;
- } else {
+ } else if (vcpu->arch.this_tsc_generation !=
+ kvm->arch.cur_tsc_generation) {
u64 tsc_exp = kvm->arch.last_tsc_write +
nsec_to_cycles(vcpu, elapsed);
u64 tsc_hz = vcpu->arch.virtual_tsc_khz * 1000LL;
@@ -2062,7 +2062,6 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr)
offset = kvm_compute_tsc_offset(vcpu, data);
}
matched = true;
- already_matched = (vcpu->arch.this_tsc_generation == kvm->arch.cur_tsc_generation);
} else {
/*
* We split periods of matched TSC writes into generations.
@@ -2102,12 +2101,10 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr)
raw_spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags);
spin_lock(&kvm->arch.pvclock_gtod_sync_lock);
- if (!matched) {
- kvm->arch.nr_vcpus_matched_tsc = 0;
- } else if (!already_matched) {
+ if (matched)
kvm->arch.nr_vcpus_matched_tsc++;
- }
-
+ else
+ kvm->arch.nr_vcpus_matched_tsc = 0;
kvm_track_tsc_matching(vcpu);
spin_unlock(&kvm->arch.pvclock_gtod_sync_lock);
}
--
2.27.0.290.gba653c62da-goog
