Zachary Amsden wrote: > When CPUs with unstable TSCs enter deep C-state, TSC may stop > running. This causes us to require resynchronization. Since > we can't tell when this may potentially happen, we assume the > worst by forcing re-compensation for it at every point the VCPU > task is descheduled. > > Is there any method to do the compensation on host TSC when recovering from C-state? It should be simpler than do it on guest TSC. > Signed-off-by: Zachary Amsden <[email protected]> > --- > arch/x86/kvm/x86.c | 11 +++++++++++ > 1 files changed, 11 insertions(+), 0 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index c8289d0..618c435 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -1822,7 +1822,18 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) > { > kvm_x86_ops->vcpu_put(vcpu); > kvm_put_guest_fpu(vcpu); > + > vcpu->arch.last_host_tsc = native_read_tsc(); > + > + /* > + * When potentially leaving a CPU with unstable TSCs, we risk > + * that the CPU enters deep C-state. If it does, the TSC may > + * go out of sync but we will not recalibrate because the test > + * vcpu->cpu != cpu can not detect this condition. So set > + * vcpu->cpu = -1 to force the recalibration above. > + */ > + if (check_tsc_unstable()) > + vcpu->cpu = -1; > } > > static int is_efer_nx(void) >
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