On Tue, May 25, 2021 at 01:05:54PM -0500, Mike Christie wrote:

-void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work)
+static void vhost_work_queue_on(struct vhost_work *work,
+				struct vhost_worker *worker)
 {
-	if (!dev->worker)
-		return;
-
 	if (!test_and_set_bit(VHOST_WORK_QUEUED, &work->flags)) {
 		/* We can only add the work to the list after we're
 		 * sure it was not in the list.
 		 * test_and_set_bit() implies a memory barrier.
 		 */
-		llist_add(&work->node, &dev->worker->work_list);
-		wake_up_process(dev->worker->task);
+		llist_add(&work->node, &worker->work_list);
+		wake_up_process(worker->task);
 	}
 }
+
+void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work)

When should this function still be used? A doc comment contrasting it to
vhost_work_queue_on() would be helpful. I would expect callers to switch
to that instead of queuing work on dev->workers[0].

 /* A lockless hint for busy polling code to exit the loop */
 bool vhost_has_work(struct vhost_dev *dev)
 {
-	return dev->worker && !llist_empty(&dev->worker->work_list);
+	int i;
+
+	for (i = 0; i < dev->num_workers; i++) {
+		if (!llist_empty(&dev->workers[i]->work_list))
+			return true;
+	}
+
+	return false;
 }
 EXPORT_SYMBOL_GPL(vhost_has_work);

It's probably not necessary to poll all workers:

drivers/vhost/net.c calls vhost_has_work() to busy poll a specific
virtqueue. If the vq:worker mapping is 1:1 or N:1 then vhost_has_work()
should be extended to include the struct vhost_virtqueue so we can poll
just that vq worker's work_list.

 /* Caller must have device mutex */
 static int vhost_worker_try_create_def(struct vhost_dev *dev)
 {
-	if (!dev->use_worker || dev->worker)
+	struct vhost_worker *worker;
+
+	if (!dev->use_worker || dev->workers)
 		return 0;
 
-	return vhost_worker_create(dev);
+	dev->workers = kcalloc(1, sizeof(struct vhost_worker *), GFP_KERNEL);

GFP_KERNEL_ACCOUNT so that vhost memory associated with a process (the
one that invoked the ioctl) is accounted? This may get trickier if the
workers are shared between processes.

The same applies for struct vhost_worker in vhost_worker_create().