virtio-serial: add enable_backend callback

We should guarantee that RAM will not be modified while VM has a stopped
state, otherwise it can lead to negative consequences during post-copy
migration. In RUN_STATE_FINISH_MIGRATE step, it's expected that RAM on
source side will not be modified as this could lead to non-consistent vm state
on the destination side. Also RAM access during postcopy-ram migration with
enabled release-ram capability can lead to sad consequences.

Let's add enable_backend() callback to avoid undesirable virtioqueue changes
in the guest memory.

Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
Message-Id: <20170919120733.22020-1-pbutsykin@virtuozzo.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/hw/char/virtio-serial-bus.c b/hw/char/virtio-serial-bus.c
index 17a1bb0..9470bd7 100644
--- a/hw/char/virtio-serial-bus.c
+++ b/hw/char/virtio-serial-bus.c
@@ -637,6 +637,13 @@ static void set_status(VirtIODevice *vdev, uint8_t status)
     if (!(status & VIRTIO_CONFIG_S_DRIVER_OK)) {
         guest_reset(vser);
     }
+
+    QTAILQ_FOREACH(port, &vser->ports, next) {
+        VirtIOSerialPortClass *vsc = VIRTIO_SERIAL_PORT_GET_CLASS(port);
+        if (vsc->enable_backend) {
+            vsc->enable_backend(port, vdev->vm_running);
+        }
+    }
 }
 
 static void vser_reset(VirtIODevice *vdev)