diff options
| -rw-r--r-- | arch/x86/kvm/x86.c | 75 |
1 files changed, 72 insertions, 3 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 6e32e87d6af6..00462bd63129 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -123,6 +123,8 @@ module_param(tsc_tolerance_ppm, uint, S_IRUGO | S_IWUSR); unsigned int __read_mostly lapic_timer_advance_ns = 0; module_param(lapic_timer_advance_ns, uint, S_IRUGO | S_IWUSR); +static bool __read_mostly backwards_tsc_observed = false; + #define KVM_NR_SHARED_MSRS 16 struct kvm_shared_msrs_global { @@ -1669,6 +1671,7 @@ static void pvclock_update_vm_gtod_copy(struct kvm *kvm) &ka->master_cycle_now); ka->use_master_clock = host_tsc_clocksource && vcpus_matched + && !backwards_tsc_observed && !ka->boot_vcpu_runs_old_kvmclock; if (ka->use_master_clock) @@ -7363,22 +7366,88 @@ int kvm_arch_hardware_enable(void) struct kvm_vcpu *vcpu; int i; int ret; + u64 local_tsc; + u64 max_tsc = 0; + bool stable, backwards_tsc = false; kvm_shared_msr_cpu_online(); ret = kvm_x86_ops->hardware_enable(); if (ret != 0) return ret; + local_tsc = rdtsc(); + stable = !check_tsc_unstable(); list_for_each_entry(kvm, &vm_list, vm_list) { kvm_for_each_vcpu(i, vcpu, kvm) { - if (vcpu->cpu == smp_processor_id()) { + if (!stable && vcpu->cpu == smp_processor_id()) kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu); - kvm_make_request(KVM_REQ_MASTERCLOCK_UPDATE, - vcpu); + if (stable && vcpu->arch.last_host_tsc > local_tsc) { + backwards_tsc = true; + if (vcpu->arch.last_host_tsc > max_tsc) + max_tsc = vcpu->arch.last_host_tsc; } } } + /* + * Sometimes, even reliable TSCs go backwards. This happens on + * platforms that reset TSC during suspend or hibernate actions, but + * maintain synchronization. We must compensate. Fortunately, we can + * detect that condition here, which happens early in CPU bringup, + * before any KVM threads can be running. Unfortunately, we can't + * bring the TSCs fully up to date with real time, as we aren't yet far + * enough into CPU bringup that we know how much real time has actually + * elapsed; our helper function, get_kernel_ns() will be using boot + * variables that haven't been updated yet. + * + * So we simply find the maximum observed TSC above, then record the + * adjustment to TSC in each VCPU. When the VCPU later gets loaded, + * the adjustment will be applied. Note that we accumulate + * adjustments, in case multiple suspend cycles happen before some VCPU + * gets a chance to run again. In the event that no KVM threads get a + * chance to run, we will miss the entire elapsed period, as we'll have + * reset last_host_tsc, so VCPUs will not have the TSC adjusted and may + * loose cycle time. This isn't too big a deal, since the loss will be + * uniform across all VCPUs (not to mention the scenario is extremely + * unlikely). It is possible that a second hibernate recovery happens + * much faster than a first, causing the observed TSC here to be + * smaller; this would require additional padding adjustment, which is + * why we set last_host_tsc to the local tsc observed here. + * + * N.B. - this code below runs only on platforms with reliable TSC, + * as that is the only way backwards_tsc is set above. Also note + * that this runs for ALL vcpus, which is not a bug; all VCPUs should + * have the same delta_cyc adjustment applied if backwards_tsc + * is detected. Note further, this adjustment is only done once, + * as we reset last_host_tsc on all VCPUs to stop this from being + * called multiple times (one for each physical CPU bringup). + * + * Platforms with unreliable TSCs don't have to deal with this, they + * will be compensated by the logic in vcpu_load, which sets the TSC to + * catchup mode. This will catchup all VCPUs to real time, but cannot + * guarantee that they stay in perfect synchronization. + */ + if (backwards_tsc) { + u64 delta_cyc = max_tsc - local_tsc; + backwards_tsc_observed = true; + list_for_each_entry(kvm, &vm_list, vm_list) { + kvm_for_each_vcpu(i, vcpu, kvm) { + vcpu->arch.tsc_offset_adjustment += delta_cyc; + vcpu->arch.last_host_tsc = local_tsc; + kvm_make_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu); + } + + /* + * We have to disable TSC offset matching.. if you were + * booting a VM while issuing an S4 host suspend.... + * you may have some problem. Solving this issue is + * left as an exercise to the reader. + */ + kvm->arch.last_tsc_nsec = 0; + kvm->arch.last_tsc_write = 0; + } + + } return 0; } |