netdev - [PATCH v5 bpf-next 3/3] veth: allow jumbo frames in xdp mode

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Date:   Fri, 11 Mar 2022 10:14:20 +0100
From:   Lorenzo Bianconi <lorenzo@...nel.org>
To:     bpf@...r.kernel.org, netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, ast@...nel.org,
        daniel@...earbox.net, brouer@...hat.com, toke@...hat.com,
        pabeni@...hat.com, echaudro@...hat.com,
        lorenzo.bianconi@...hat.com, toshiaki.makita1@...il.com,
        andrii@...nel.org
Subject: [PATCH v5 bpf-next 3/3] veth: allow jumbo frames in xdp mode

Allow increasing the MTU over page boundaries on veth devices
if the attached xdp program declares to support xdp fragments.

Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
---
 drivers/net/veth.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index bfae15ec902b..1b5714926d81 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -1528,9 +1528,14 @@ static int veth_xdp_set(struct net_device *dev, struct bpf_prog *prog,
 			goto err;
 		}
 
-		max_mtu = PAGE_SIZE - VETH_XDP_HEADROOM -
-			  peer->hard_header_len -
-			  SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+		max_mtu = SKB_WITH_OVERHEAD(PAGE_SIZE - VETH_XDP_HEADROOM) -
+			  peer->hard_header_len;
+		/* Allow increasing the max_mtu if the program supports
+		 * XDP fragments.
+		 */
+		if (prog->aux->xdp_has_frags)
+			max_mtu += PAGE_SIZE * MAX_SKB_FRAGS;
+
 		if (peer->mtu > max_mtu) {
 			NL_SET_ERR_MSG_MOD(extack, "Peer MTU is too large to set XDP");
 			err = -ERANGE;
-- 
2.35.1