netdev - [bpf-next PATCH] xdp: accept that XDP headroom isn't always equal XDP_PACKET

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Date:   Tue, 03 Mar 2020 12:46:58 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     bpf@...r.kernel.org
Cc:     Jesper Dangaard Brouer <brouer@...hat.com>, gamemann@...clan.com,
        lrizzo@...gle.com, netdev@...r.kernel.org,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Toke Høiland-Jørgensen <toke@...e.dk>
Subject: [bpf-next PATCH] xdp: accept that XDP headroom isn't always equal
 XDP_PACKET_HEADROOM

The Intel based drivers (ixgbe + i40e) have implemented XDP with
headroom 192 bytes and not the recommended 256 bytes defined by
XDP_PACKET_HEADROOM.  For generic-XDP, accept that this headroom
is also a valid size.

Still for generic-XDP if headroom is less, still expand headroom to
XDP_PACKET_HEADROOM as this is the default in most XDP drivers.

Tested on ixgbe with xdp_rxq_info --skb-mode and --action XDP_DROP:
- Before: 4,816,430 pps
- After : 7,749,678 pps
(Note that ixgbe in native mode XDP_DROP 14,704,539 pps)

Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
---
 include/uapi/linux/bpf.h |    1 +
 net/core/dev.c           |    4 ++--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 906e9f2752db..14dc4f9fb3c8 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3312,6 +3312,7 @@ struct bpf_xdp_sock {
 };
 
 #define XDP_PACKET_HEADROOM 256
+#define XDP_PACKET_HEADROOM_MIN 192
 
 /* User return codes for XDP prog type.
  * A valid XDP program must return one of these defined values. All other
diff --git a/net/core/dev.c b/net/core/dev.c
index 4770dde3448d..9c941cd38b13 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4518,11 +4518,11 @@ static u32 netif_receive_generic_xdp(struct sk_buff *skb,
 		return XDP_PASS;
 
 	/* XDP packets must be linear and must have sufficient headroom
-	 * of XDP_PACKET_HEADROOM bytes. This is the guarantee that also
+	 * of XDP_PACKET_HEADROOM_MIN bytes. This is the guarantee that also
 	 * native XDP provides, thus we need to do it here as well.
 	 */
 	if (skb_cloned(skb) || skb_is_nonlinear(skb) ||
-	    skb_headroom(skb) < XDP_PACKET_HEADROOM) {
+	    skb_headroom(skb) < XDP_PACKET_HEADROOM_MIN) {
 		int hroom = XDP_PACKET_HEADROOM - skb_headroom(skb);
 		int troom = skb->tail + skb->data_len - skb->end;