Zachary Amsden wrote: > SMP VMs on machines with unstable TSC have their TSC offset adjusted by the > local offset delta from last measurement. This does not take into account how > long it has been since the measurement, leading to drift. Minimize the drift > by accounting for any time difference the kernel has observed. > > Signed-off-by: Zachary Amsden <zams...@redhat.com> > --- > arch/x86/include/asm/kvm_host.h | 1 + > arch/x86/kvm/x86.c | 20 +++++++++++++++++++- > 2 files changed, 20 insertions(+), 1 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 94f6ce8..1afecd7 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -337,6 +337,7 @@ struct kvm_vcpu_arch { > unsigned int time_offset; > struct page *time_page; > u64 last_host_tsc; > + u64 last_host_ns; > > bool nmi_pending; > bool nmi_injected; > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 618c435..b1bdf05 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -1810,6 +1810,19 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) > /* Make sure TSC doesn't go backwards */ > s64 tsc_delta = !vcpu->arch.last_host_tsc ? 0 : > native_read_tsc() - vcpu->arch.last_host_tsc; > + > + /* Subtract elapsed cycle time from the delta computation */ > + if (check_tsc_unstable() && vcpu->arch.last_host_ns) { > + s64 delta; > + struct timespec ts; > + ktime_get_ts(&ts); > + monotonic_to_bootbased(&ts); > + delta = timespec_to_ns(&ts) - vcpu->arch.last_host_ns; > + delta = delta * per_cpu(cpu_tsc_khz, cpu); > This seems not work well on a cpu w/o CONSTANT_TSC. > + delta = delta / USEC_PER_SEC; > + tsc_delta -= delta; > + } > + > if (tsc_delta < 0 || check_tsc_unstable()) > kvm_x86_ops->adjust_tsc_offset(vcpu, -tsc_delta); > kvm_migrate_timers(vcpu); > @@ -1832,8 +1845,13 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) > * vcpu->cpu != cpu can not detect this condition. So set > * vcpu->cpu = -1 to force the recalibration above. > */ > - if (check_tsc_unstable()) > + if (check_tsc_unstable()) { > + struct timespec ts; > + ktime_get_ts(&ts); > + monotonic_to_bootbased(&ts); > + vcpu->arch.last_host_ns = timespec_to_ns(&ts); > vcpu->cpu = -1; > + } > } > > static int is_efer_nx(void) >
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