[PATCH 4.4 29/52] xen/netfront: read response from backend only once

Greg Kroah-Hartman
2021-12-06T15:00:29Z

From: Juergen Gross <jgross@suse.com>

commit 8446066bf8c1f9f7b7412c43fbea0fb87464d75b upstream.

In order to avoid problems in case the backend is modifying a response
on the ring page while the frontend has already seen it, just read the
response into a local buffer in one go and then operate on that buffer
only.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/xen-netfront.c | 38 +++++++++++++++++++-------------------
1 file changed, 19 insertions(+), 19 deletions(-)

--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -387,13 +387,13 @@ static void xennet_tx_buf_gc(struct netf
rmb(); /* Ensure we see responses up to 'rp'. */

for (cons = queue->tx.rsp_cons; cons != prod; cons++) {
- struct xen_netif_tx_response *txrsp;
+ struct xen_netif_tx_response txrsp;

- txrsp = RING_GET_RESPONSE(&queue->tx, cons);
- if (txrsp->status == XEN_NETIF_RSP_NULL)
+ RING_COPY_RESPONSE(&queue->tx, cons, &txrsp);
+ if (txrsp.status == XEN_NETIF_RSP_NULL)
continue;

- id = txrsp->id;
+ id = txrsp.id;
skb = queue->tx_skbs[id].skb;
if (unlikely(gnttab_query_foreign_access(
queue->grant_tx_ref[id]) != 0)) {
@@ -736,7 +736,7 @@ static int xennet_get_extras(struct netf
RING_IDX rp)

{
- struct xen_netif_extra_info *extra;
+ struct xen_netif_extra_info extra;
struct device *dev = &queue->info->netdev->dev;
RING_IDX cons = queue->rx.rsp_cons;
int err = 0;
@@ -752,24 +752,22 @@ static int xennet_get_extras(struct netf
break;
}

- extra = (struct xen_netif_extra_info *)
- RING_GET_RESPONSE(&queue->rx, ++cons);
+ RING_COPY_RESPONSE(&queue->rx, ++cons, &extra);

- if (unlikely(!extra->type ||
- extra->type >= XEN_NETIF_EXTRA_TYPE_MAX)) {
+ if (unlikely(!extra.type ||
+ extra.type >= XEN_NETIF_EXTRA_TYPE_MAX)) {
if (net_ratelimit())
dev_warn(dev, "Invalid extra type: %d\n",
- extra->type);
+ extra.type);
err = -EINVAL;
} else {
- memcpy(&extras[extra->type - 1], extra,
- sizeof(*extra));
+ extras[extra.type - 1] = extra;
}

skb = xennet_get_rx_skb(queue, cons);
ref = xennet_get_rx_ref(queue, cons);
xennet_move_rx_slot(queue, skb, ref);
- } while (extra->flags & XEN_NETIF_EXTRA_FLAG_MORE);
+ } while (extra.flags & XEN_NETIF_EXTRA_FLAG_MORE);

queue->rx.rsp_cons = cons;
return err;
@@ -779,7 +777,7 @@ static int xennet_get_responses(struct n
struct netfront_rx_info *rinfo, RING_IDX rp,
struct sk_buff_head *list)
{
- struct xen_netif_rx_response *rx = &rinfo->rx;
+ struct xen_netif_rx_response *rx = &rinfo->rx, rx_local;
struct xen_netif_extra_info *extras = rinfo->extras;
struct device *dev = &queue->info->netdev->dev;
RING_IDX cons = queue->rx.rsp_cons;
@@ -837,7 +835,8 @@ next:
break;
}

- rx = RING_GET_RESPONSE(&queue->rx, cons + slots);
+ RING_COPY_RESPONSE(&queue->rx, cons + slots, &rx_local);
+ rx = &rx_local;
skb = xennet_get_rx_skb(queue, cons + slots);
ref = xennet_get_rx_ref(queue, cons + slots);
slots++;
@@ -892,10 +891,11 @@ static int xennet_fill_frags(struct netf
struct sk_buff *nskb;

while ((nskb = __skb_dequeue(list))) {
- struct xen_netif_rx_response *rx =
- RING_GET_RESPONSE(&queue->rx, ++cons);
+ struct xen_netif_rx_response rx;
skb_frag_t *nfrag = &skb_shinfo(nskb)->frags[0];

+ RING_COPY_RESPONSE(&queue->rx, ++cons, &rx);
+
if (skb_shinfo(skb)->nr_frags == MAX_SKB_FRAGS) {
unsigned int pull_to = NETFRONT_SKB_CB(skb)->pull_to;

@@ -910,7 +910,7 @@ static int xennet_fill_frags(struct netf

skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags,
skb_frag_page(nfrag),
- rx->offset, rx->status, PAGE_SIZE);
+ rx.offset, rx.status, PAGE_SIZE);

skb_shinfo(nskb)->nr_frags = 0;
kfree_skb(nskb);
@@ -1008,7 +1008,7 @@ static int xennet_poll(struct napi_struc
i = queue->rx.rsp_cons;
work_done = 0;
while ((i != rp) && (work_done < budget)) {
- memcpy(rx, RING_GET_RESPONSE(&queue->rx, i), sizeof(*rx));
+ RING_COPY_RESPONSE(&queue->rx, i, rx);
memset(extras, 0, sizeof(rinfo.extras));

err = xennet_get_responses(queue, &rinfo, rp, &tmpq);