virtio-serial-bus: post_load send_event when vm is running

Alexander Larsson found irq injection to Windows guests stopped after a
migration.  The symptom was the mouse stopped working.

Reproduction steps are:
1. On src, start qemu with a virtio-serial port without any backend
2. On dest, start qemu with a virtio-serial port with a backend
3. Migrate.

Upon migration, the older code detected the change in backend connection
status, and sent a notification to the guest.  However, it's not
guaranteed that the apic is ready to inject irqs into the guest, and the
irq line remained high, resulting in any future interrupts going
unnoticed by the guest as well.

Add a new timer based on vm_clock for 1 ns in the future from post_load
to do the event send in case host_connected differs between migration
source and target.

RHBZ: 867366

Signed-off-by: Alon Levy <alevy@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com> # verbose commit log

hw/virtio-serial-bus.c

@@ -53,6 +53,15 @@ struct VirtIOSerial {
     uint32_t *ports_map;
 
     struct virtio_console_config config;
+
+    struct {
+        QEMUTimer *timer;
+        int nr_active_ports;
+        struct {
+            VirtIOSerialPort *port;
+            uint8_t host_connected;
+        } *connected;
+    } post_load;
 };
 
 static VirtIOSerialPort *find_port_by_id(VirtIOSerial *vser, uint32_t id)
@@ -626,6 +635,29 @@ static void virtio_serial_save(QEMUFile *f, void *opaque)
     }
 }
 
+static void virtio_serial_post_load_timer_cb(void *opaque)
+{
+    int i;
+    VirtIOSerial *s = opaque;
+    VirtIOSerialPort *port;
+    uint8_t host_connected;
+
+    for (i = 0 ; i < s->post_load.nr_active_ports; ++i) {
+        port = s->post_load.connected[i].port;
+        host_connected = s->post_load.connected[i].host_connected;
+        if (host_connected != port->host_connected) {
+            /*
+             * We have to let the guest know of the host connection
+             * status change
+             */
+            send_control_event(port, VIRTIO_CONSOLE_PORT_OPEN,
+                               port->host_connected);
+        }
+    }
+    g_free(s->post_load.connected);
+    s->post_load.connected = NULL;
+}
+
 static int virtio_serial_load(QEMUFile *f, void *opaque, int version_id)
 {
     VirtIOSerial *s = opaque;
@@ -673,10 +705,13 @@ static int virtio_serial_load(QEMUFile *f, void *opaque, int version_id)
 
     qemu_get_be32s(f, &nr_active_ports);
 
+    s->post_load.nr_active_ports = nr_active_ports;
+    s->post_load.connected =
+        g_malloc0(sizeof(*s->post_load.connected) * nr_active_ports);
+
     /* Items in struct VirtIOSerialPort */
     for (i = 0; i < nr_active_ports; i++) {
         uint32_t id;
-        bool host_connected;
 
         id = qemu_get_be32(f);
         port = find_port_by_id(s, id);
@@ -685,15 +720,8 @@ static int virtio_serial_load(QEMUFile *f, void *opaque, int version_id)
         }
 
         port->guest_connected = qemu_get_byte(f);
-        host_connected = qemu_get_byte(f);
+        s->post_load.connected[i].port = port;
-        if (host_connected != port->host_connected) {
+        s->post_load.connected[i].host_connected = qemu_get_byte(f);
-            /*
-             * We have to let the guest know of the host connection
-             * status change
-             */
-            send_control_event(port, VIRTIO_CONSOLE_PORT_OPEN,
-                               port->host_connected);
-        }
 
         if (version_id > 2) {
             uint32_t elem_popped;
@@ -718,6 +746,7 @@ static int virtio_serial_load(QEMUFile *f, void *opaque, int version_id)
             }
         }
     }
+    qemu_mod_timer(s->post_load.timer, 1);
     return 0;
 }
 
@@ -967,6 +996,9 @@ VirtIODevice *virtio_serial_init(DeviceState *dev, virtio_serial_conf *conf)
     register_savevm(dev, "virtio-console", -1, 3, virtio_serial_save,
                     virtio_serial_load, vser);
 
+    vser->post_load.timer = qemu_new_timer_ns(vm_clock,
+            virtio_serial_post_load_timer_cb, vser);
+
     return vdev;
 }
 
@@ -979,6 +1011,8 @@ void virtio_serial_exit(VirtIODevice *vdev)
     g_free(vser->ivqs);
     g_free(vser->ovqs);
     g_free(vser->ports_map);
+    g_free(vser->post_load.connected);
+    qemu_free_timer(vser->post_load.timer);
 
     virtio_cleanup(vdev);
 }