virtio: Prevent creation of device using notification-data with ioeventfd

Prevent the realization of a virtio device that attempts to use the
VIRTIO_F_NOTIFICATION_DATA transport feature without disabling
ioeventfd.

Due to ioeventfd not being able to carry the extra data associated with
this feature, having both enabled is a functional mismatch and therefore
Qemu should not continue the device's realization process.

Although the device does not yet know if the feature will be
successfully negotiated, many devices using this feature wont actually
work without this extra data and would fail FEATURES_OK anyway.

If ioeventfd is able to work with the extra notification data in the
future, this compatibility check can be removed.

Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
Message-Id: <20240315165557.26942-3-jonah.palmer@oracle.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index f7c99e3a965e4c3ca18a577a3cf30602f5eb9a8d..28cd406e1684c870121bd9a00c8b7774a81c0f97 100644 (file)
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -2980,6 +2980,20 @@ int virtio_set_features(VirtIODevice *vdev, uint64_t val)
     return ret;
 }
 
+static void virtio_device_check_notification_compatibility(VirtIODevice *vdev,
+                                                           Error **errp)
+{
+    VirtioBusState *bus = VIRTIO_BUS(qdev_get_parent_bus(DEVICE(vdev)));
+    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(bus);
+    DeviceState *proxy = DEVICE(BUS(bus)->parent);
+
+    if (virtio_host_has_feature(vdev, VIRTIO_F_NOTIFICATION_DATA) &&
+        k->ioeventfd_enabled(proxy)) {
+        error_setg(errp,
+                   "notification_data=on without ioeventfd=off is not supported");
+    }
+}
+
 size_t virtio_get_config_size(const VirtIOConfigSizeParams *params,
                               uint64_t host_features)
 {
@@ -3740,6 +3754,14 @@ static void virtio_device_realize(DeviceState *dev, Error **errp)
         }
     }
 
+    /* Devices should not use both ioeventfd and notification data feature */
+    virtio_device_check_notification_compatibility(vdev, &err);
+    if (err != NULL) {
+        error_propagate(errp, err);
+        vdc->unrealize(dev);
+        return;
+    }
+
     virtio_bus_device_plugged(vdev, &err);
     if (err != NULL) {
         error_propagate(errp, err);