diff options
| -rw-r--r-- | arch/x86/include/asm/kvm_host.h | 1 | ||||
| -rw-r--r-- | arch/x86/kvm/x86.c | 93 |
2 files changed, 89 insertions, 5 deletions
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index dd439f13df8..4fbeb84b181 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -423,6 +423,7 @@ struct kvm_vcpu_arch { u64 last_tsc_nsec; u64 last_tsc_write; u64 last_host_tsc; + u64 tsc_offset_adjustment; bool tsc_catchup; bool tsc_always_catchup; s8 virtual_tsc_shift; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 3b931302fa5..4e9bd23d522 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2252,6 +2252,14 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) } kvm_x86_ops->vcpu_load(vcpu, cpu); + + /* Apply any externally detected TSC adjustments (due to suspend) */ + if (unlikely(vcpu->arch.tsc_offset_adjustment)) { + adjust_tsc_offset_host(vcpu, vcpu->arch.tsc_offset_adjustment); + vcpu->arch.tsc_offset_adjustment = 0; + set_bit(KVM_REQ_CLOCK_UPDATE, &vcpu->requests); + } + if (unlikely(vcpu->cpu != cpu) || check_tsc_unstable()) { s64 tsc_delta = !vcpu->arch.last_host_tsc ? 0 : native_read_tsc() - vcpu->arch.last_host_tsc; @@ -5964,13 +5972,88 @@ int kvm_arch_hardware_enable(void *garbage) struct kvm *kvm; 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(); - list_for_each_entry(kvm, &vm_list, vm_list) - kvm_for_each_vcpu(i, vcpu, kvm) - if (vcpu->cpu == smp_processor_id()) - kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu); - return kvm_x86_ops->hardware_enable(garbage); + ret = kvm_x86_ops->hardware_enable(garbage); + if (ret != 0) + return ret; + + local_tsc = native_read_tsc(); + stable = !check_tsc_unstable(); + list_for_each_entry(kvm, &vm_list, vm_list) { + kvm_for_each_vcpu(i, vcpu, kvm) { + if (!stable && vcpu->cpu == smp_processor_id()) + set_bit(KVM_REQ_CLOCK_UPDATE, &vcpu->requests); + 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 unnreliable 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; + 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; + } + + /* + * 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; } void kvm_arch_hardware_disable(void *garbage) |