veth: Xdp using frame_sz in veth driver

The veth driver can run XDP in "native" mode in it's own NAPI
handler, and since commit 9fc8d518d9d5 ("veth: Handle xdp_frames in
xdp napi ring") packets can come in two forms either xdp_frame or
skb, calling respectively veth_xdp_rcv_one() or veth_xdp_rcv_skb().

For packets to arrive in xdp_frame format, they will have been
redirected from an XDP native driver. In case of XDP_PASS or no
XDP-prog attached, the veth driver will allocate and create an SKB.

The current code in veth_xdp_rcv_one() xdp_frame case, had to guess
the frame truesize of the incoming xdp_frame, when using
veth_build_skb(). With xdp_frame->frame_sz this is not longer
necessary.

Calculating the frame_sz in veth_xdp_rcv_skb() skb case, is done
similar to the XDP-generic handling code in net/core/dev.c.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Lorenzo Bianconi <lorenzo@kernel.org>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Acked-by: Toshiaki Makita <toshiaki.makita1@gmail.com>
Link: https://lore.kernel.org/bpf/158945338840.97035.935897116345700902.stgit@firesoul

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index d5691bb84448c4d35f80b26725dc98dfd374e2cb..b586d2fa555151a31473d405616ac6aea1af759c 100644 (file)
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -405,10 +405,6 @@ static struct sk_buff *veth_build_skb(void *head, int headroom, int len,
 {
        struct sk_buff *skb;
 
-       if (!buflen) {
-               buflen = SKB_DATA_ALIGN(headroom + len) +
-                        SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
-       }
        skb = build_skb(head, buflen);
        if (!skb)
                return NULL;
@@ -583,6 +579,7 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq,
                xdp.data = frame->data;
                xdp.data_end = frame->data + frame->len;
                xdp.data_meta = frame->data - frame->metasize;
+               xdp.frame_sz = frame->frame_sz;
                xdp.rxq = &rq->xdp_rxq;
 
                act = bpf_prog_run_xdp(xdp_prog, &xdp);
@@ -629,7 +626,7 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq,
        rcu_read_unlock();
 
        headroom = sizeof(struct xdp_frame) + frame->headroom - delta;
-       skb = veth_build_skb(hard_start, headroom, len, 0);
+       skb = veth_build_skb(hard_start, headroom, len, frame->frame_sz);
        if (!skb) {
                xdp_return_frame(frame);
                stats->rx_drops++;
@@ -695,9 +692,8 @@ static struct sk_buff *veth_xdp_rcv_skb(struct veth_rq *rq,
                        goto drop;
                }
 
-               nskb = veth_build_skb(head,
-                                     VETH_XDP_HEADROOM + mac_len, skb->len,
-                                     PAGE_SIZE);
+               nskb = veth_build_skb(head, VETH_XDP_HEADROOM + mac_len,
+                                     skb->len, PAGE_SIZE);
                if (!nskb) {
                        page_frag_free(head);
                        goto drop;
@@ -715,6 +711,11 @@ static struct sk_buff *veth_xdp_rcv_skb(struct veth_rq *rq,
        xdp.data_end = xdp.data + pktlen;
        xdp.data_meta = xdp.data;
        xdp.rxq = &rq->xdp_rxq;
+
+       /* SKB "head" area always have tailroom for skb_shared_info */
+       xdp.frame_sz = (void *)skb_end_pointer(skb) - xdp.data_hard_start;
+       xdp.frame_sz += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+
        orig_data = xdp.data;
        orig_data_end = xdp.data_end;
 
@@ -758,6 +759,7 @@ static struct sk_buff *veth_xdp_rcv_skb(struct veth_rq *rq,
        }
        rcu_read_unlock();
 
+       /* check if bpf_xdp_adjust_head was used */
        delta = orig_data - xdp.data;
        off = mac_len + delta;
        if (off > 0)
@@ -765,9 +767,11 @@ static struct sk_buff *veth_xdp_rcv_skb(struct veth_rq *rq,
        else if (off < 0)
                __skb_pull(skb, -off);
        skb->mac_header -= delta;
+
+       /* check if bpf_xdp_adjust_tail was used */
        off = xdp.data_end - orig_data_end;
        if (off != 0)
-               __skb_put(skb, off);
+               __skb_put(skb, off); /* positive on grow, negative on shrink */
        skb->protocol = eth_type_trans(skb, rq->dev);
 
        metalen = xdp.data - xdp.data_meta;