Commit 9476654b authored by Paul Durrant's avatar Paul Durrant Committed by David S. Miller
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xen-netback: support dynamic unbind/bind 



By re-attaching RX, TX, and CTL rings during connect() rather than
assuming they are freshly allocated (i.e. assuming the counters are zero),
and avoiding forcing state to Closed in netback_remove() it is possible
for vif instances to be unbound and re-bound from and to (respectively) a
running guest.

Dynamic unbind/bind is a highly useful feature for a backend module as it
allows it to be unloaded and re-loaded (i.e. updated) without requiring
domUs to be halted.

This has been tested by running iperf as a server in the test VM and
then running a client against it in a continuous loop, whilst also
running:

while true;
  do echo vif-$DOMID-$VIF >unbind;
  echo down;
  rmmod xen-netback;
  echo unloaded;
  modprobe xen-netback;
  cd $(pwd);
  brctl addif xenbr0 vif$DOMID.$VIF;
  ip link set vif$DOMID.$VIF up;
  echo up;
  sleep 5;
  done

in dom0 from /sys/bus/xen-backend/drivers/vif to continuously unbind,
unload, re-load, re-bind and re-plumb the backend.

Clearly a performance drop was seen but no TCP connection resets were
observed during this test and moreover a parallel SSH connection into the
guest remained perfectly usable throughout.

Signed-off-by: default avatarPaul Durrant <pdurrant@amazon.com>
Reviewed-by: default avatarWei Liu <wei.liu@kernel.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 8d347992

drivers/net/xen-netback/interface.c

+9 −1
Original line number Diff line number Diff line
@@ -585,6 +585,7 @@ int xenvif_connect_ctrl(struct xenvif *vif, grant_ref_t ring_ref, 
	struct net_device *dev = vif->dev;

	void *addr;

	struct xen_netif_ctrl_sring *shared;

	RING_IDX rsp_prod, req_prod;

	int err;



	err = xenbus_map_ring_valloc(xenvif_to_xenbus_device(vif),
@@ -593,7 +594,14 @@ int xenvif_connect_ctrl(struct xenvif *vif, grant_ref_t ring_ref, 
		goto err;



	shared = (struct xen_netif_ctrl_sring *)addr;

	BACK_RING_INIT(&vif->ctrl, shared, XEN_PAGE_SIZE);

	rsp_prod = READ_ONCE(shared->rsp_prod);

	req_prod = READ_ONCE(shared->req_prod);



	BACK_RING_ATTACH(&vif->ctrl, shared, rsp_prod, XEN_PAGE_SIZE);



	err = -EIO;

	if (req_prod - rsp_prod > RING_SIZE(&vif->ctrl))

		goto err_unmap;



	err = bind_interdomain_evtchn_to_irq(vif->domid, evtchn);

	if (err < 0)

drivers/net/xen-netback/netback.c

+17 −3
Original line number Diff line number Diff line
@@ -1453,7 +1453,7 @@ int xenvif_map_frontend_data_rings(struct xenvif_queue *queue, 
	void *addr;

	struct xen_netif_tx_sring *txs;

	struct xen_netif_rx_sring *rxs;



	RING_IDX rsp_prod, req_prod;

	int err = -ENOMEM;



	err = xenbus_map_ring_valloc(xenvif_to_xenbus_device(queue->vif),
@@ -1462,7 +1462,14 @@ int xenvif_map_frontend_data_rings(struct xenvif_queue *queue, 
		goto err;



	txs = (struct xen_netif_tx_sring *)addr;

	BACK_RING_INIT(&queue->tx, txs, XEN_PAGE_SIZE);

	rsp_prod = READ_ONCE(txs->rsp_prod);

	req_prod = READ_ONCE(txs->req_prod);



	BACK_RING_ATTACH(&queue->tx, txs, rsp_prod, XEN_PAGE_SIZE);



	err = -EIO;

	if (req_prod - rsp_prod > RING_SIZE(&queue->tx))

		goto err;



	err = xenbus_map_ring_valloc(xenvif_to_xenbus_device(queue->vif),

				     &rx_ring_ref, 1, &addr);
@@ -1470,7 +1477,14 @@ int xenvif_map_frontend_data_rings(struct xenvif_queue *queue, 
		goto err;



	rxs = (struct xen_netif_rx_sring *)addr;

	BACK_RING_INIT(&queue->rx, rxs, XEN_PAGE_SIZE);

	rsp_prod = READ_ONCE(rxs->rsp_prod);

	req_prod = READ_ONCE(rxs->req_prod);



	BACK_RING_ATTACH(&queue->rx, rxs, rsp_prod, XEN_PAGE_SIZE);



	err = -EIO;

	if (req_prod - rsp_prod > RING_SIZE(&queue->rx))

		goto err;



	return 0;

drivers/net/xen-netback/xenbus.c

+2 −3
Original line number Diff line number Diff line
@@ -954,12 +954,10 @@ static int netback_remove(struct xenbus_device *dev) 
{

	struct backend_info *be = dev_get_drvdata(&dev->dev);



	set_backend_state(be, XenbusStateClosed);



	unregister_hotplug_status_watch(be);

	if (be->vif) {

		kobject_uevent(&dev->dev.kobj, KOBJ_OFFLINE);

		xen_unregister_watchers(be->vif);

		backend_disconnect(be);

		xenvif_free(be->vif);

		be->vif = NULL;

	}
@@ -1131,6 +1129,7 @@ static struct xenbus_driver netback_driver = { 
	.remove = netback_remove,

	.uevent = netback_uevent,

	.otherend_changed = frontend_changed,

	.allow_rebind = true,

};



int xenvif_xenbus_init(void)

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