2 files changed, 107 insertions, 3 deletions

diff --git a/hw/s390x/tod-kvm.c b/hw/s390x/tod-kvm.c
index df564ab89c..2456bf7b24 100644
--- a/hw/s390x/tod-kvm.c
+++ b/hw/s390x/tod-kvm.c
@@ -10,10 +10,11 @@
 
 #include "qemu/osdep.h"
 #include "qapi/error.h"
+#include "sysemu/sysemu.h"
 #include "hw/s390x/tod.h"
 #include "kvm_s390x.h"
 
-static void kvm_s390_tod_get(const S390TODState *td, S390TOD *tod, Error **errp)
+static void kvm_s390_get_tod_raw(S390TOD *tod, Error **errp)
 {
     int r;
 
@@ -27,7 +28,17 @@ static void kvm_s390_tod_get(const S390TODState *td, S390TOD *tod, Error **errp)
     }
 }
 
-static void kvm_s390_tod_set(S390TODState *td, const S390TOD *tod, Error **errp)
+static void kvm_s390_tod_get(const S390TODState *td, S390TOD *tod, Error **errp)
+{
+    if (td->stopped) {
+        *tod = td->base;
+        return;
+    }
+
+    kvm_s390_get_tod_raw(tod, errp);
+}
+
+static void kvm_s390_set_tod_raw(const S390TOD *tod, Error **errp)
 {
     int r;
 
@@ -41,18 +52,105 @@ static void kvm_s390_tod_set(S390TODState *td, const S390TOD *tod, Error **errp)
     }
 }
 
+static void kvm_s390_tod_set(S390TODState *td, const S390TOD *tod, Error **errp)
+{
+    Error *local_err = NULL;
+
+    /*
+     * Somebody (e.g. migration) set the TOD. We'll store it into KVM to
+     * properly detect errors now but take a look at the runstate to decide
+     * whether really to keep the tod running. E.g. during migration, this
+     * is the point where we want to stop the initially running TOD to fire
+     * it back up when actually starting the migrated guest.
+     */
+    kvm_s390_set_tod_raw(tod, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        return;
+    }
+
+    if (runstate_is_running()) {
+        td->stopped = false;
+    } else {
+        td->stopped = true;
+        td->base = *tod;
+    }
+}
+
+static void kvm_s390_tod_vm_state_change(void *opaque, int running,
+                                         RunState state)
+{
+    S390TODState *td = opaque;
+    Error *local_err = NULL;
+
+    if (running && td->stopped) {
+        /* Set the old TOD when running the VM - start the TOD clock. */
+        kvm_s390_set_tod_raw(&td->base, &local_err);
+        if (local_err) {
+            warn_report_err(local_err);
+        }
+        /* Treat errors like the TOD was running all the time. */
+        td->stopped = false;
+    } else if (!running && !td->stopped) {
+        /* Store the TOD when stopping the VM - stop the TOD clock. */
+        kvm_s390_get_tod_raw(&td->base, &local_err);
+        if (local_err) {
+            /* Keep the TOD running in case we could not back it up. */
+            warn_report_err(local_err);
+        } else {
+            td->stopped = true;
+        }
+    }
+}
+
+static void kvm_s390_tod_realize(DeviceState *dev, Error **errp)
+{
+    S390TODState *td = S390_TOD(dev);
+    S390TODClass *tdc = S390_TOD_GET_CLASS(td);
+    Error *local_err = NULL;
+
+    tdc->parent_realize(dev, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        return;
+    }
+
+    /*
+     * We need to know when the VM gets started/stopped to start/stop the TOD.
+     * As we can never have more than one TOD instance (and that will never be
+     * removed), registering here and never unregistering is good enough.
+     */
+    qemu_add_vm_change_state_handler(kvm_s390_tod_vm_state_change, td);
+}
+
 static void kvm_s390_tod_class_init(ObjectClass *oc, void *data)
 {
     S390TODClass *tdc = S390_TOD_CLASS(oc);
 
+    device_class_set_parent_realize(DEVICE_CLASS(oc), kvm_s390_tod_realize,
+                                    &tdc->parent_realize);
     tdc->get = kvm_s390_tod_get;
     tdc->set = kvm_s390_tod_set;
 }
 
+static void kvm_s390_tod_init(Object *obj)
+{
+    S390TODState *td = S390_TOD(obj);
+
+    /*
+     * The TOD is initially running (value stored in KVM). Avoid needless
+     * loading/storing of the TOD when starting a simple VM, so let it
+     * run although the (never started) VM is stopped. For migration, we
+     * will properly set the TOD later.
+     */
+    td->stopped = false;
+}
+
 static TypeInfo kvm_s390_tod_info = {
     .name = TYPE_KVM_S390_TOD,
     .parent = TYPE_S390_TOD,
     .instance_size = sizeof(S390TODState),
+    .instance_init = kvm_s390_tod_init,
     .class_init = kvm_s390_tod_class_init,
     .class_size = sizeof(S390TODClass),
 };
diff --git a/include/hw/s390x/tod.h b/include/hw/s390x/tod.h
index 413c0d7c02..cbd7552e7a 100644
--- a/include/hw/s390x/tod.h
+++ b/include/hw/s390x/tod.h
@@ -31,13 +31,19 @@ typedef struct S390TODState {
     /* private */
     DeviceState parent_obj;
 
-    /* unused by KVM implementation */
+    /*
+     * Used by TCG to remember the time base. Used by KVM to backup the TOD
+     * while the TOD is stopped.
+     */
     S390TOD base;
+    /* Used by KVM to remember if the TOD is stopped and base is valid. */
+    bool stopped;
 } S390TODState;
 
 typedef struct S390TODClass {
     /* private */
     DeviceClass parent_class;
+    void (*parent_realize)(DeviceState *dev, Error **errp);
 
     /* public */
     void (*get)(const S390TODState *td, S390TOD *tod, Error **errp);