diff options
Diffstat (limited to 'arch/x86/kvm/x86.c')
| -rw-r--r-- | arch/x86/kvm/x86.c | 41 |
1 files changed, 1 insertions, 40 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 0fd2bd78fccf..842abd33e9b5 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1487,7 +1487,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) unsigned long flags, this_tsc_khz; struct kvm_vcpu_arch *vcpu = &v->arch; struct kvm_arch *ka = &v->kvm->arch; - s64 kernel_ns, max_kernel_ns; + s64 kernel_ns; u64 tsc_timestamp, host_tsc; struct pvclock_vcpu_time_info guest_hv_clock; u8 pvclock_flags; @@ -1546,37 +1546,6 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) if (!vcpu->pv_time_enabled) return 0; - /* - * Time as measured by the TSC may go backwards when resetting the base - * tsc_timestamp. The reason for this is that the TSC resolution is - * higher than the resolution of the other clock scales. Thus, many - * possible measurments of the TSC correspond to one measurement of any - * other clock, and so a spread of values is possible. This is not a - * problem for the computation of the nanosecond clock; with TSC rates - * around 1GHZ, there can only be a few cycles which correspond to one - * nanosecond value, and any path through this code will inevitably - * take longer than that. However, with the kernel_ns value itself, - * the precision may be much lower, down to HZ granularity. If the - * first sampling of TSC against kernel_ns ends in the low part of the - * range, and the second in the high end of the range, we can get: - * - * (TSC - offset_low) * S + kns_old > (TSC - offset_high) * S + kns_new - * - * As the sampling errors potentially range in the thousands of cycles, - * it is possible such a time value has already been observed by the - * guest. To protect against this, we must compute the system time as - * observed by the guest and ensure the new system time is greater. - */ - max_kernel_ns = 0; - if (vcpu->hv_clock.tsc_timestamp) { - max_kernel_ns = vcpu->last_guest_tsc - - vcpu->hv_clock.tsc_timestamp; - max_kernel_ns = pvclock_scale_delta(max_kernel_ns, - vcpu->hv_clock.tsc_to_system_mul, - vcpu->hv_clock.tsc_shift); - max_kernel_ns += vcpu->last_kernel_ns; - } - if (unlikely(vcpu->hw_tsc_khz != this_tsc_khz)) { kvm_get_time_scale(NSEC_PER_SEC / 1000, this_tsc_khz, &vcpu->hv_clock.tsc_shift, @@ -1584,14 +1553,6 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) vcpu->hw_tsc_khz = this_tsc_khz; } - /* with a master <monotonic time, tsc value> tuple, - * pvclock clock reads always increase at the (scaled) rate - * of guest TSC - no need to deal with sampling errors. - */ - if (!use_master_clock) { - if (max_kernel_ns > kernel_ns) - kernel_ns = max_kernel_ns; - } /* With all the info we got, fill in the values */ vcpu->hv_clock.tsc_timestamp = tsc_timestamp; vcpu->hv_clock.system_time = kernel_ns + v->kvm->arch.kvmclock_offset; |