[PATCH v2 2/6] virtio: Prevent creation of device using notification-data with ioeventfd

[Jonah Palmer <jonah.palmer@oracle.com>]

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>
---
 hw/virtio/virtio.c         | 22 ++++++++++++++++++++++
 include/hw/virtio/virtio.h |  2 ++
 2 files changed, 24 insertions(+)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index bcb9e09df0..d0a433b465 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -2971,6 +2971,20 @@ int virtio_set_features(VirtIODevice *vdev, uint64_t val)
     return ret;
 }
 
+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)
 {
@@ -3731,6 +3745,14 @@ 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);
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 53915947a7..e0325d84d0 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -346,6 +346,8 @@ void virtio_queue_reset(VirtIODevice *vdev, uint32_t queue_index);
 void virtio_queue_enable(VirtIODevice *vdev, uint32_t queue_index);
 void virtio_update_irq(VirtIODevice *vdev);
 int virtio_set_features(VirtIODevice *vdev, uint64_t val);
+void virtio_device_check_notification_compatibility(VirtIODevice *vdev,
+                                                    Error **errp);
 
 /* Base devices.  */
 typedef struct VirtIOBlkConf VirtIOBlkConf;
-- 
2.39.3