Fix virtio migration when the device is down If the guest did not initalize the pfn, don't use it

index 69fe810..1367af1 100644
@@ -192,10 +192,15 @@ void virtio_dev_save(QEMUFile *f, VirtIODevice *vdev)
     for(i = 0; i < VIRTIO_PCI_QUEUE_MAX; i++) {
         if (!vdev->vq[i].vring.num)
             continue;
+
         qemu_put_be32s(f, &vdev->vq[i].pfn);
         qemu_put_be16s(f, &vdev->vq[i].last_avail_idx);
         qemu_put_be32s(f, &vdev->vq[i].index);
 
+        /* The guest does not have the driver active */
+        if (!vdev->vq[i].pfn)
+            continue;
+
         /* Save the descriptor ring instead of constantly mark them dirty */
         qemu_put_buffer(f, (uint8_t*)vdev->vq[i].vring.desc, vdev->vq[i].vring.num * sizeof(VRingDesc));
         qemu_put_buffer(f, (uint8_t*)vdev->vq[i].vring.avail, TARGET_PAGE_SIZE);

@@ -220,9 +225,14 @@ int virtio_dev_load(QEMUFile *f, VirtIODevice *vdev, int version_id)
      for(i = 0; i < VIRTIO_PCI_QUEUE_MAX; i++) {
          if (!vdev->vq[i].vring.num)
              continue;
+
          qemu_get_be32s(f, &vdev->vq[i].pfn);
          qemu_get_be16s(f, &vdev->vq[i].last_avail_idx);
          qemu_get_be32s(f, &vdev->vq[i].index);
+         /* The guest does not have the driver active */
+         if (!vdev->vq[i].pfn)
+             continue;
+
          virtqueue_init(&vdev->vq[i], phys_ram_base +
                                       (vdev->vq[i].pfn << TARGET_PAGE_BITS));
          qemu_get_buffer(f, (uint8_t*)vdev->vq[i].vring.desc, vdev->vq[i].vring.num * sizeof(VRingDesc));