+/*
+ * This callback is executed during stop_machine(). All CPUs are therefore
+ * temporarily stopped. In order not to change guest behavior, we have to
+ * disable preemption whenever we touch the epoch of kvm and the VCPUs,
+ * so a CPU won't be stopped while calculating with the epoch.
+ */
+static int kvm_clock_sync(struct notifier_block *notifier, unsigned long val,
+ void *v)
+{
+ struct kvm *kvm;
+ struct kvm_vcpu *vcpu;
+ int i;
+ unsigned long long *delta = v;
+
+ list_for_each_entry(kvm, &vm_list, vm_list) {
+ kvm->arch.epoch -= *delta;
+ kvm_for_each_vcpu(i, vcpu, kvm) {
+ vcpu->arch.sie_block->epoch -= *delta;
+ }
+ }
+ return NOTIFY_OK;
+}
+
+static struct notifier_block kvm_clock_notifier = {
+ .notifier_call = kvm_clock_sync,
+};
+