1 files changed, 46 insertions, 1 deletions

diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index b341dd62aa4d..9a36051ceb76 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -57,6 +57,11 @@ struct virtio_shm_region {
  *		include a NULL entry for vqs unused by driver
  *	Returns 0 on success or error status
  * @del_vqs: free virtqueues found by find_vqs().
+ * @synchronize_cbs: synchronize with the virtqueue callbacks (optional)
+ *      The function guarantees that all memory operations on the
+ *      queue before it are visible to the vring_interrupt() that is
+ *      called after it.
+ *      vdev: the virtio_device
  * @get_features: get the array of feature bits for this device.
  *	vdev: the virtio_device
  *	Returns the first 64 feature bits (all we currently need).
@@ -89,6 +94,7 @@ struct virtio_config_ops {
 			const char * const names[], const bool *ctx,
 			struct irq_affinity *desc);
 	void (*del_vqs)(struct virtio_device *);
+	void (*synchronize_cbs)(struct virtio_device *);
 	u64 (*get_features)(struct virtio_device *vdev);
 	int (*finalize_features)(struct virtio_device *vdev);
 	const char *(*bus_name)(struct virtio_device *vdev);
@@ -218,6 +224,25 @@ int virtio_find_vqs_ctx(struct virtio_device *vdev, unsigned nvqs,
 }
 
 /**
+ * virtio_synchronize_cbs - synchronize with virtqueue callbacks
+ * @vdev: the device
+ */
+static inline
+void virtio_synchronize_cbs(struct virtio_device *dev)
+{
+	if (dev->config->synchronize_cbs) {
+		dev->config->synchronize_cbs(dev);
+	} else {
+		/*
+		 * A best effort fallback to synchronize with
+		 * interrupts, preemption and softirq disabled
+		 * regions. See comment above synchronize_rcu().
+		 */
+		synchronize_rcu();
+	}
+}
+
+/**
  * virtio_device_ready - enable vq use in probe function
  * @vdev: the device
  *
@@ -230,7 +255,27 @@ void virtio_device_ready(struct virtio_device *dev)
 {
 	unsigned status = dev->config->get_status(dev);
 
-	BUG_ON(status & VIRTIO_CONFIG_S_DRIVER_OK);
+	WARN_ON(status & VIRTIO_CONFIG_S_DRIVER_OK);
+
+	/*
+	 * The virtio_synchronize_cbs() makes sure vring_interrupt()
+	 * will see the driver specific setup if it sees vq->broken
+	 * as false (even if the notifications come before DRIVER_OK).
+	 */
+	virtio_synchronize_cbs(dev);
+	__virtio_unbreak_device(dev);
+	/*
+	 * The transport should ensure the visibility of vq->broken
+	 * before setting DRIVER_OK. See the comments for the transport
+	 * specific set_status() method.
+	 *
+	 * A well behaved device will only notify a virtqueue after
+	 * DRIVER_OK, this means the device should "see" the coherenct
+	 * memory write that set vq->broken as false which is done by
+	 * the driver when it sees DRIVER_OK, then the following
+	 * driver's vring_interrupt() will see vq->broken as false so
+	 * we won't lose any notification.
+	 */
 	dev->config->set_status(dev, status | VIRTIO_CONFIG_S_DRIVER_OK);
 }