[PATCH v3 net-next 2/2] xdp: add multi-buff support for xdp running in generic mode

[Lorenzo Bianconi <lorenzo@kernel.org>]

Similar to native xdp, do not always linearize the skb in
netif_receive_generic_xdp routine but create a non-linear xdp_buff to be
processed by the eBPF program. This allow to add  multi-buffer support
for xdp running in generic mode.

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 net/core/dev.c | 151 +++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 126 insertions(+), 25 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 4df68d7f04a2..ed827b443d48 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4853,6 +4853,12 @@ u32 bpf_prog_run_generic_xdp(struct sk_buff *skb, struct xdp_buff *xdp,
 	xdp_init_buff(xdp, frame_sz, &rxqueue->xdp_rxq);
 	xdp_prepare_buff(xdp, hard_start, skb_headroom(skb) - mac_len,
 			 skb_headlen(skb) + mac_len, true);
+	if (skb_is_nonlinear(skb)) {
+		skb_shinfo(skb)->xdp_frags_size = skb->data_len;
+		xdp_buff_set_frags_flag(xdp);
+	} else {
+		xdp_buff_clear_frags_flag(xdp);
+	}
 
 	orig_data_end = xdp->data_end;
 	orig_data = xdp->data;
@@ -4882,6 +4888,14 @@ u32 bpf_prog_run_generic_xdp(struct sk_buff *skb, struct xdp_buff *xdp,
 		skb->len += off; /* positive on grow, negative on shrink */
 	}
 
+	/* XDP frag metadata (e.g. nr_frags) are updated in eBPF helpers
+	 * (e.g. bpf_xdp_adjust_tail), we need to update data_len here.
+	 */
+	if (xdp_buff_has_frags(xdp))
+		skb->data_len = skb_shinfo(skb)->xdp_frags_size;
+	else
+		skb->data_len = 0;
+
 	/* check if XDP changed eth hdr such SKB needs update */
 	eth = (struct ethhdr *)xdp->data;
 	if ((orig_eth_type != eth->h_proto) ||
@@ -4915,54 +4929,141 @@ u32 bpf_prog_run_generic_xdp(struct sk_buff *skb, struct xdp_buff *xdp,
 	return act;
 }
 
-static u32 netif_receive_generic_xdp(struct sk_buff **pskb,
-				     struct xdp_buff *xdp,
-				     struct bpf_prog *xdp_prog)
+static int netif_skb_check_for_generic_xdp(struct sk_buff **pskb,
+					   struct bpf_prog *prog)
 {
 	struct sk_buff *skb = *pskb;
-	u32 act = XDP_DROP;
-
-	/* Reinjected packets coming from act_mirred or similar should
-	 * not get XDP generic processing.
-	 */
-	if (skb_is_redirected(skb))
-		return XDP_PASS;
+	int err;
 
-	/* XDP packets must be linear and must have sufficient headroom
-	 * of XDP_PACKET_HEADROOM bytes. This is the guarantee that also
-	 * native XDP provides, thus we need to do it here as well.
+	/* XDP does not support fraglist so we need to linearize
+	 * the skb.
 	 */
-	if (skb_cloned(skb) || skb_is_nonlinear(skb) ||
-	    skb_headroom(skb) < XDP_PACKET_HEADROOM) {
+	if (skb_has_frag_list(skb) || !prog->aux->xdp_has_frags) {
 		int hroom = XDP_PACKET_HEADROOM - skb_headroom(skb);
 		int troom = skb->tail + skb->data_len - skb->end;
 
 		/* In case we have to go down the path and also linearize,
 		 * then lets do the pskb_expand_head() work just once here.
 		 */
-		if (pskb_expand_head(skb,
-				     hroom > 0 ? ALIGN(hroom, NET_SKB_PAD) : 0,
-				     troom > 0 ? troom + 128 : 0, GFP_ATOMIC))
-			goto do_drop;
-		if (skb_linearize(skb))
-			goto do_drop;
+		err = pskb_expand_head(skb,
+				       hroom > 0 ? ALIGN(hroom, NET_SKB_PAD) : 0,
+				       troom > 0 ? troom + 128 : 0, GFP_ATOMIC);
+		if (err)
+			return err;
+
+		err = skb_linearize(skb);
+		if (err)
+			return err;
+
+		return 0;
 	}
 
-	act = bpf_prog_run_generic_xdp(skb, xdp, xdp_prog);
+	/* XDP packets must have sufficient headroom of XDP_PACKET_HEADROOM
+	 * bytes. This is the guarantee that also native XDP provides,
+	 * thus we need to do it here as well.
+	 */
+	if (skb_cloned(skb) || skb_shinfo(skb)->nr_frags ||
+	    skb_headroom(skb) < XDP_PACKET_HEADROOM) {
+		u32 mac_len = skb->data - skb_mac_header(skb);
+		u32 size, truesize, len, max_head_size, off;
+		struct sk_buff *nskb;
+		int i, head_off;
+		void *data;
+
+		__skb_push(skb, mac_len);
+		max_head_size = SKB_WITH_OVERHEAD(PAGE_SIZE -
+						  XDP_PACKET_HEADROOM);
+		if (skb->len > max_head_size + MAX_SKB_FRAGS * PAGE_SIZE)
+			return -ENOMEM;
+
+		size = min_t(u32, skb->len, max_head_size);
+		truesize = SKB_HEAD_ALIGN(size) + XDP_PACKET_HEADROOM;
+		data = napi_alloc_frag(truesize);
+		if (!data)
+			return -ENOMEM;
+
+		nskb = napi_build_skb(data, truesize);
+		if (!nskb) {
+			skb_free_frag(data);
+			return -ENOMEM;
+		}
+
+		skb_reserve(nskb, XDP_PACKET_HEADROOM);
+		skb_copy_header(nskb, skb);
+
+		err = skb_copy_bits(skb, 0, nskb->data, size);
+		if (err) {
+			consume_skb(nskb);
+			return err;
+		}
+		skb_put(nskb, size);
+
+		head_off = skb_headroom(nskb) - skb_headroom(skb);
+		skb_headers_offset_update(nskb, head_off);
+
+		off = size;
+		len = skb->len - off;
+		for (i = 0; i < MAX_SKB_FRAGS && off < skb->len; i++) {
+			struct page *page;
+
+			size = min_t(u32, len, PAGE_SIZE);
+			data = napi_alloc_frag(size);
+			if (!data) {
+				consume_skb(nskb);
+				return -ENOMEM;
+			}
+
+			page = virt_to_head_page(data);
+			skb_add_rx_frag(nskb, i, page,
+					data - page_address(page), size, size);
+			err = skb_copy_bits(skb, off, data, size);
+			if (err) {
+				consume_skb(nskb);
+				return err;
+			}
+
+			len -= size;
+			off += size;
+		}
+
+		consume_skb(skb);
+		*pskb = nskb;
+		__skb_pull(nskb, mac_len);
+	}
+
+	return 0;
+}
+
+static u32 netif_receive_generic_xdp(struct sk_buff **pskb,
+				     struct xdp_buff *xdp,
+				     struct bpf_prog *xdp_prog)
+{
+	u32 act = XDP_DROP;
+
+	/* Reinjected packets coming from act_mirred or similar should
+	 * not get XDP generic processing.
+	 */
+	if (skb_is_redirected(*pskb))
+		return XDP_PASS;
+
+	if (netif_skb_check_for_generic_xdp(pskb, xdp_prog))
+		goto do_drop;
+
+	act = bpf_prog_run_generic_xdp(*pskb, xdp, xdp_prog);
 	switch (act) {
 	case XDP_REDIRECT:
 	case XDP_TX:
 	case XDP_PASS:
 		break;
 	default:
-		bpf_warn_invalid_xdp_action(skb->dev, xdp_prog, act);
+		bpf_warn_invalid_xdp_action((*pskb)->dev, xdp_prog, act);
 		fallthrough;
 	case XDP_ABORTED:
-		trace_xdp_exception(skb->dev, xdp_prog, act);
+		trace_xdp_exception((*pskb)->dev, xdp_prog, act);
 		fallthrough;
 	case XDP_DROP:
 	do_drop:
-		kfree_skb(skb);
+		kfree_skb(*pskb);
 		break;
 	}
 
-- 
2.43.0