@@ -77,6 +77,16 @@ static int s390_virtio_hcall_notify(const uint64_t *args)
if (mem > ram_size) {
VirtIOS390Device *dev = s390_virtio_bus_find_vring(s390_bus, mem, &i);
if (dev) {
+ /*
+ * Older kernels will use the virtqueue before setting DRIVER_OK.
+ * In this case the feature bits are not yet up to date, meaning
+ * that several funny things can happen, e.g. the guest thinks
+ * EVENT_IDX is on and QEMU thinks it is off. Let's force a feature
+ * and status sync.
+ */
+ if (!(dev->vdev->status & VIRTIO_CONFIG_S_DRIVER_OK)) {
+ s390_virtio_device_update_status(dev);
+ }
virtio_queue_notify(dev->vdev, i);
} else {
r = -EINVAL;