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Subject[PATCH net V2] virtio-net: re enable XDP_REDIRECT for mergeable buffer
Date
XDP_REDIRECT support for mergeable buffer was removed since commit
7324f5399b06 ("virtio_net: disable XDP_REDIRECT in receive_mergeable()
case"). This is because we don't reserve enough tailroom for struct
skb_shared_info which breaks XDP assumption. So this patch fixes this
by reserving enough tailroom and using fixed size of rx buffer.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
Changes from V1:
- do not add duplicated tracepoint when redirection fails
---
drivers/net/virtio_net.c | 54 +++++++++++++++++++++++++++++++++++++-----------
1 file changed, 42 insertions(+), 12 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 9bb9e56..426dcf7 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -504,6 +504,7 @@ static struct page *xdp_linearize_page(struct receive_queue *rq,
page_off += *len;

while (--*num_buf) {
+ int tailroom = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
unsigned int buflen;
void *buf;
int off;
@@ -518,7 +519,7 @@ static struct page *xdp_linearize_page(struct receive_queue *rq,
/* guard against a misconfigured or uncooperative backend that
* is sending packet larger than the MTU.
*/
- if ((page_off + buflen) > PAGE_SIZE) {
+ if ((page_off + buflen + tailroom) > PAGE_SIZE) {
put_page(p);
goto err_buf;
}
@@ -690,6 +691,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
unsigned int truesize;
unsigned int headroom = mergeable_ctx_to_headroom(ctx);
bool sent;
+ int err;

head_skb = NULL;

@@ -701,7 +703,12 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
void *data;
u32 act;

- /* This happens when rx buffer size is underestimated */
+ /* This happens when rx buffer size is underestimated
+ * or headroom is not enough because of the buffer
+ * was refilled before XDP is set. This should only
+ * happen for the first several packets, so we don't
+ * care much about its performance.
+ */
if (unlikely(num_buf > 1 ||
headroom < virtnet_get_headroom(vi))) {
/* linearize data for XDP */
@@ -736,9 +743,6 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,

act = bpf_prog_run_xdp(xdp_prog, &xdp);

- if (act != XDP_PASS)
- ewma_pkt_len_add(&rq->mrg_avg_pkt_len, len);
-
switch (act) {
case XDP_PASS:
/* recalculate offset to account for any header
@@ -770,6 +774,18 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
goto err_xdp;
rcu_read_unlock();
goto xdp_xmit;
+ case XDP_REDIRECT:
+ err = xdp_do_redirect(dev, &xdp, xdp_prog);
+ if (err) {
+ if (unlikely(xdp_page != page))
+ put_page(xdp_page);
+ goto err_xdp;
+ }
+ *xdp_xmit = true;
+ if (unlikely(xdp_page != page))
+ goto err_xdp;
+ rcu_read_unlock();
+ goto xdp_xmit;
default:
bpf_warn_invalid_xdp_action(act);
case XDP_ABORTED:
@@ -1013,13 +1029,18 @@ static int add_recvbuf_big(struct virtnet_info *vi, struct receive_queue *rq,
}

static unsigned int get_mergeable_buf_len(struct receive_queue *rq,
- struct ewma_pkt_len *avg_pkt_len)
+ struct ewma_pkt_len *avg_pkt_len,
+ unsigned int room)
{
const size_t hdr_len = sizeof(struct virtio_net_hdr_mrg_rxbuf);
unsigned int len;

- len = hdr_len + clamp_t(unsigned int, ewma_pkt_len_read(avg_pkt_len),
+ if (room)
+ return PAGE_SIZE - room;
+
+ len = hdr_len + clamp_t(unsigned int, ewma_pkt_len_read(avg_pkt_len),
rq->min_buf_len, PAGE_SIZE - hdr_len);
+
return ALIGN(len, L1_CACHE_BYTES);
}

@@ -1028,21 +1049,27 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
{
struct page_frag *alloc_frag = &rq->alloc_frag;
unsigned int headroom = virtnet_get_headroom(vi);
+ unsigned int tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
+ unsigned int room = SKB_DATA_ALIGN(headroom + tailroom);
char *buf;
void *ctx;
int err;
unsigned int len, hole;

- len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len);
- if (unlikely(!skb_page_frag_refill(len + headroom, alloc_frag, gfp)))
+ /* Extra tailroom is needed to satisfy XDP's assumption. This
+ * means rx frags coalescing won't work, but consider we've
+ * disabled GSO for XDP, it won't be a big issue.
+ */
+ len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room);
+ if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp)))
return -ENOMEM;

buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset;
buf += headroom; /* advance address leaving hole at front of pkt */
get_page(alloc_frag->page);
- alloc_frag->offset += len + headroom;
+ alloc_frag->offset += len + room;
hole = alloc_frag->size - alloc_frag->offset;
- if (hole < len + headroom) {
+ if (hole < len + room) {
/* To avoid internal fragmentation, if there is very likely not
* enough space for another buffer, add the remaining space to
* the current buffer.
@@ -2576,12 +2603,15 @@ static ssize_t mergeable_rx_buffer_size_show(struct netdev_rx_queue *queue,
{
struct virtnet_info *vi = netdev_priv(queue->dev);
unsigned int queue_index = get_netdev_rx_queue_index(queue);
+ unsigned int headroom = virtnet_get_headroom(vi);
+ unsigned int tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
struct ewma_pkt_len *avg;

BUG_ON(queue_index >= vi->max_queue_pairs);
avg = &vi->rq[queue_index].mrg_avg_pkt_len;
return sprintf(buf, "%u\n",
- get_mergeable_buf_len(&vi->rq[queue_index], avg));
+ get_mergeable_buf_len(&vi->rq[queue_index], avg,
+ SKB_DATA_ALIGN(headroom + tailroom)));
}

static struct rx_queue_attribute mergeable_rx_buffer_size_attribute =
--
2.7.4
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