virtio-net: re enable XDP_REDIRECT for mergeable buffer

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>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 42 insertions, 12 deletions

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 9bb9e562b893..426dcf7dad4a 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 =