vhost: fix vhost_dev_enable_notifiers() error case

in vhost_dev_enable_notifiers(), if virtio_bus_set_host_notifier(true)
fails, we call vhost_dev_disable_notifiers() that executes
virtio_bus_set_host_notifier(false) on all queues, even on queues that
have failed to be initialized.

This triggers a core dump in memory_region_del_eventfd():

 virtio_bus_set_host_notifier: unable to init event notifier: Too many open files (-24)
 vhost VQ 1 notifier binding failed: 24
 .../softmmu/memory.c:2611: memory_region_del_eventfd: Assertion `i != mr->ioeventfd_nb' failed.

Fix the problem by providing to vhost_dev_disable_notifiers() the
number of queues to disable.

Fixes: 8771589 ("vhost: simplify vhost_dev_enable_notifiers")
Cc: longpeng2@huawei.com
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Message-Id: <20230602162735.3670785-1-lvivier@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

hw/virtio/vhost.c

@@ -1530,6 +1530,40 @@ void vhost_dev_cleanup(struct vhost_dev *hdev)
     memset(hdev, 0, sizeof(struct vhost_dev));
 }
 
+static void vhost_dev_disable_notifiers_nvqs(struct vhost_dev *hdev,
+                                             VirtIODevice *vdev,
+                                             unsigned int nvqs)
+{
+    BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(vdev)));
+    int i, r;
+
+    /*
+     * Batch all the host notifiers in a single transaction to avoid
+     * quadratic time complexity in address_space_update_ioeventfds().
+     */
+    memory_region_transaction_begin();
+
+    for (i = 0; i < nvqs; ++i) {
+        r = virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), hdev->vq_index + i,
+                                         false);
+        if (r < 0) {
+            error_report("vhost VQ %d notifier cleanup failed: %d", i, -r);
+        }
+        assert(r >= 0);
+    }
+
+    /*
+     * The transaction expects the ioeventfds to be open when it
+     * commits. Do it now, before the cleanup loop.
+     */
+    memory_region_transaction_commit();
+
+    for (i = 0; i < nvqs; ++i) {
+        virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), hdev->vq_index + i);
+    }
+    virtio_device_release_ioeventfd(vdev);
+}
+
 /* Stop processing guest IO notifications in qemu.
  * Start processing them in vhost in kernel.
  */
@@ -1559,7 +1593,7 @@ int vhost_dev_enable_notifiers(struct vhost_dev *hdev, VirtIODevice *vdev)
         if (r < 0) {
             error_report("vhost VQ %d notifier binding failed: %d", i, -r);
             memory_region_transaction_commit();
-            vhost_dev_disable_notifiers(hdev, vdev);
+            vhost_dev_disable_notifiers_nvqs(hdev, vdev, i);
             return r;
         }
     }
@@ -1576,34 +1610,7 @@ int vhost_dev_enable_notifiers(struct vhost_dev *hdev, VirtIODevice *vdev)
  */
 void vhost_dev_disable_notifiers(struct vhost_dev *hdev, VirtIODevice *vdev)
 {
-    BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(vdev)));
-    int i, r;
-
-    /*
-     * Batch all the host notifiers in a single transaction to avoid
-     * quadratic time complexity in address_space_update_ioeventfds().
-     */
-    memory_region_transaction_begin();
-
-    for (i = 0; i < hdev->nvqs; ++i) {
-        r = virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), hdev->vq_index + i,
-                                         false);
-        if (r < 0) {
-            error_report("vhost VQ %d notifier cleanup failed: %d", i, -r);
-        }
-        assert (r >= 0);
-    }
-
-    /*
-     * The transaction expects the ioeventfds to be open when it
-     * commits. Do it now, before the cleanup loop.
-     */
-    memory_region_transaction_commit();
-
-    for (i = 0; i < hdev->nvqs; ++i) {
-        virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), hdev->vq_index + i);
-    }
-    virtio_device_release_ioeventfd(vdev);
+    vhost_dev_disable_notifiers_nvqs(hdev, vdev, hdev->nvqs);
 }
 
 /* Test and clear event pending status.