x86: kvm: introduce periodic global clock updates

commit 0061d53 introduced a mechanism to execute a global clock
update for a vm. We can apply this periodically in order to propagate
host NTP corrections. Also, if all vcpus of a vm are pinned, then
without an additional trigger, no guest NTP corrections can propagate
either, as the current trigger is only vcpu cpu migration.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -599,6 +599,7 @@ struct kvm_arch {
 	u64 master_kernel_ns;
 	cycle_t master_cycle_now;
 	struct delayed_work kvmclock_update_work;
+	struct delayed_work kvmclock_sync_work;
 
 	struct kvm_xen_hvm_config xen_hvm_config;
 

arch/x86/kvm/x86.c

@@ -1660,6 +1660,20 @@ static void kvm_gen_kvmclock_update(struct kvm_vcpu *v)
 					KVMCLOCK_UPDATE_DELAY);
 }
 
+#define KVMCLOCK_SYNC_PERIOD (300 * HZ)
+
+static void kvmclock_sync_fn(struct work_struct *work)
+{
+	struct delayed_work *dwork = to_delayed_work(work);
+	struct kvm_arch *ka = container_of(dwork, struct kvm_arch,
+					   kvmclock_sync_work);
+	struct kvm *kvm = container_of(ka, struct kvm, arch);
+
+	schedule_delayed_work(&kvm->arch.kvmclock_update_work, 0);
+	schedule_delayed_work(&kvm->arch.kvmclock_sync_work,
+					KVMCLOCK_SYNC_PERIOD);
+}
+
 static bool msr_mtrr_valid(unsigned msr)
 {
 	switch (msr) {
@@ -6736,6 +6750,7 @@ int kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
 {
 	int r;
 	struct msr_data msr;
+	struct kvm *kvm = vcpu->kvm;
 
 	r = vcpu_load(vcpu);
 	if (r)
@@ -6746,6 +6761,9 @@ int kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
 	kvm_write_tsc(vcpu, &msr);
 	vcpu_put(vcpu);
 
+	schedule_delayed_work(&kvm->arch.kvmclock_sync_work,
+					KVMCLOCK_SYNC_PERIOD);
+
 	return r;
 }
 
@@ -7039,6 +7057,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 	pvclock_update_vm_gtod_copy(kvm);
 
 	INIT_DELAYED_WORK(&kvm->arch.kvmclock_update_work, kvmclock_update_fn);
+	INIT_DELAYED_WORK(&kvm->arch.kvmclock_sync_work, kvmclock_sync_fn);
 
 	return 0;
 }
@@ -7077,6 +7096,7 @@ static void kvm_free_vcpus(struct kvm *kvm)
 
 void kvm_arch_sync_events(struct kvm *kvm)
 {
+	cancel_delayed_work_sync(&kvm->arch.kvmclock_sync_work);
 	cancel_delayed_work_sync(&kvm->arch.kvmclock_update_work);
 	kvm_free_all_assigned_devices(kvm);
 	kvm_free_pit(kvm);