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xen-netback: support dynamic unbind/bind

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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: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: Wei Liu <wei.liu@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Paul Durrant
2019-12-23 09:59:23 +00:00
committed by David S. Miller
parent 8d34799298
commit 9476654bd5
3 changed files with 28 additions and 7 deletions
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20
drivers/net/xen-netback/netback.c
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@@ -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;