virtio: reset function

A reset function solves three problems:

1) It allows us to renegotiate features, eg. if we want to upgrade a
   guest driver without rebooting the guest.

2) It gives us a clean way of shutting down virtqueues: after a reset,
   we know that the buffers won't be used by the host, and

3) It helps the guest recover from messed-up drivers.

So we remove the ->shutdown hook, and the only way we now remove
feature bits is via reset.

We leave it to the driver to do the reset before it deletes queues:
the balloon driver, for example, needs to chat to the host in its
remove function.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

5 files changed, 31 insertions, 17 deletions

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 54a8017ad487..6143337527e7 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -264,12 +264,16 @@ static void virtblk_remove(struct virtio_device *vdev)
         struct virtio_blk *vblk = vdev->priv;
         int major = vblk->disk->major;
 
+        /* Nothing should be pending. */
         BUG_ON(!list_empty(&vblk->reqs));
+
+        /* Stop all the virtqueues. */
+        vdev->config->reset(vdev);
+
         blk_cleanup_queue(vblk->disk->queue);
         put_disk(vblk->disk);
         unregister_blkdev(major, "virtblk");
         mempool_destroy(vblk->pool);
-        /* There should be nothing in the queue now, so no need to shutdown */
         vdev->config->del_vq(vblk->vq);
         kfree(vblk);
 }
diff --git a/drivers/lguest/lguest_device.c b/drivers/lguest/lguest_device.c
index ced5b44cebce..84f85e23cca7 100644
--- a/drivers/lguest/lguest_device.c
+++ b/drivers/lguest/lguest_device.c
@@ -54,7 +54,7 @@ struct lguest_device {
  *
  * The configuration information for a device consists of one or more
  * virtqueues, a feature bitmaks, and some configuration bytes.  The
- * configuration bytes don't really matter to us: the Launcher set them up, and
+ * configuration bytes don't really matter to us: the Launcher sets them up, and
  * the driver will look at them during setup.
  *
  * A convenient routine to return the device's virtqueue config array:
@@ -139,9 +139,20 @@ static u8 lg_get_status(struct virtio_device *vdev)
 
 static void lg_set_status(struct virtio_device *vdev, u8 status)
 {
+        BUG_ON(!status);
         to_lgdev(vdev)->desc->status = status;
 }
 
+/* To reset the device, we (ab)use the NOTIFY hypercall, with the descriptor
+ * address of the device.  The Host will zero the status and all the
+ * features. */
+static void lg_reset(struct virtio_device *vdev)
+{
+        unsigned long offset = (void *)to_lgdev(vdev)->desc - lguest_devices;
+
+        hcall(LHCALL_NOTIFY, (max_pfn<<PAGE_SHIFT) + offset, 0, 0);
+}
+
 /*
  * Virtqueues
  *
@@ -279,6 +290,7 @@ static struct virtio_config_ops lguest_config_ops = {
         .set = lg_set,
         .get_status = lg_get_status,
         .set_status = lg_set_status,
+        .reset = lg_reset,
         .find_vq = lg_find_vq,
         .del_vq = lg_del_vq,
 };
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index ec43284ffd13..6e0a9fefe6cb 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -390,13 +390,14 @@ static void virtnet_remove(struct virtio_device *vdev)
         struct virtnet_info *vi = vdev->priv;
         struct sk_buff *skb;
 
+        /* Stop all the virtqueues. */
+        vdev->config->reset(vdev);
+
         /* Free our skbs in send and recv queues, if any. */
-        vi->rvq->vq_ops->shutdown(vi->rvq);
         while ((skb = __skb_dequeue(&vi->recv)) != NULL) {
                 kfree_skb(skb);
                 vi->num--;
         }
-        vi->svq->vq_ops->shutdown(vi->svq);
         while ((skb = __skb_dequeue(&vi->send)) != NULL)
                 kfree_skb(skb);
 
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 303cb6f90108..7dddb1860936 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -102,9 +102,13 @@ static int virtio_dev_remove(struct device *_d)
         struct virtio_driver *drv = container_of(dev->dev.driver,
                                                  struct virtio_driver, driver);
 
-        dev->config->set_status(dev, dev->config->get_status(dev)
-                                & ~VIRTIO_CONFIG_S_DRIVER);
         drv->remove(dev);
+
+        /* Driver should have reset device. */
+        BUG_ON(dev->config->get_status(dev));
+
+        /* Acknowledge the device's existence again. */
+        add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE);
         return 0;
 }
 
@@ -130,6 +134,10 @@ int register_virtio_device(struct virtio_device *dev)
         dev->dev.bus = &virtio_bus;
         sprintf(dev->dev.bus_id, "%u", dev->index);
 
+        /* We always start by resetting the device, in case a previous
+         * driver messed it up.  This also tests that code path a little. */
+        dev->config->reset(dev);
+
         /* Acknowledge that we've seen the device. */
         add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE);
 
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index dbe1d35db32a..9849babd6b37 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -173,16 +173,6 @@ static void detach_buf(struct vring_virtqueue *vq, unsigned int head)
         vq->num_free++;
 }
 
-/* FIXME: We need to tell other side about removal, to synchronize. */
-static void vring_shutdown(struct virtqueue *_vq)
-{
-        struct vring_virtqueue *vq = to_vvq(_vq);
-        unsigned int i;
-
-        for (i = 0; i < vq->vring.num; i++)
-                detach_buf(vq, i);
-}
-
 static inline bool more_used(const struct vring_virtqueue *vq)
 {
         return vq->last_used_idx != vq->vring.used->idx;
@@ -278,7 +268,6 @@ static struct virtqueue_ops vring_vq_ops = {
         .kick = vring_kick,
         .disable_cb = vring_disable_cb,
         .enable_cb = vring_enable_cb,
-        .shutdown = vring_shutdown,
 };
 
 struct virtqueue *vring_new_virtqueue(unsigned int num,