Merge branch 'xdp-grow-tail'

Jesper Dangaard Brouer says:

====================
V4:
- Fixup checkpatch.pl issues
- Collected more ACKs

V3:
- Fix issue on virtio_net patch spotted by Jason Wang
- Adjust name for variable in mlx5 patch
- Collected more ACKs

V2:
- Fix bug in mlx5 for XDP_PASS case
- Collected nitpicks and ACKs from mailing list

V1:
- Fix bug in dpaa2

XDP have evolved to support several frame sizes, but xdp_buff was not
updated with this information. This have caused the side-effect that
XDP frame data hard end is unknown. This have limited the BPF-helper
bpf_xdp_adjust_tail to only shrink the packet. This patchset address
this and add packet tail extend/grow.

The purpose of the patchset is ALSO to reserve a memory area that can be
used for storing extra information, specifically for extending XDP with
multi-buffer support. One proposal is to use same layout as
skb_shared_info, which is why this area is currently 320 bytes.

When converting xdp_frame to SKB (veth and cpumap), the full tailroom
area can now be used and SKB truesize is now correct. For most
drivers this result in a much larger tailroom in SKB "head" data
area. The network stack can now take advantage of this when doing SKB
coalescing. Thus, a good driver test is to use xdp_redirect_cpu from
samples/bpf/ and do some TCP stream testing.

Use-cases for tail grow/extend:
(1) IPsec / XFRM needs a tail extend[1][2].
(2) DNS-cache responses in XDP.
(3) HAProxy ALOHA would need it to convert to XDP.
(4) Add tail info e.g. timestamp and collect via tcpdump

[1] http://vger.kernel.org/netconf2019_files/xfrm_xdp.pdf
[2] http://vger.kernel.org/netconf2019.html

Examples on howto access the tail area of an XDP packet is shown in the
XDP-tutorial example[3].

[3] https://github.com/xdp-project/xdp-tutorial/blob/master/experiment01-tailgrow/
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 12 insertions, 4 deletions

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index 29dbdd4c29f6..30ba7d38941d 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -470,25 +470,34 @@ out:
 int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
 			  union bpf_attr __user *uattr)
 {
+	u32 tailroom = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+	u32 headroom = XDP_PACKET_HEADROOM;
 	u32 size = kattr->test.data_size_in;
 	u32 repeat = kattr->test.repeat;
 	struct netdev_rx_queue *rxqueue;
 	struct xdp_buff xdp = {};
 	u32 retval, duration;
+	u32 max_data_sz;
 	void *data;
 	int ret;
 
 	if (kattr->test.ctx_in || kattr->test.ctx_out)
 		return -EINVAL;
 
-	data = bpf_test_init(kattr, size, XDP_PACKET_HEADROOM + NET_IP_ALIGN, 0);
+	/* XDP have extra tailroom as (most) drivers use full page */
+	max_data_sz = 4096 - headroom - tailroom;
+	if (size > max_data_sz)
+		return -EINVAL;
+
+	data = bpf_test_init(kattr, max_data_sz, headroom, tailroom);
 	if (IS_ERR(data))
 		return PTR_ERR(data);
 
 	xdp.data_hard_start = data;
-	xdp.data = data + XDP_PACKET_HEADROOM + NET_IP_ALIGN;
+	xdp.data = data + headroom;
 	xdp.data_meta = xdp.data;
 	xdp.data_end = xdp.data + size;
+	xdp.frame_sz = headroom + max_data_sz + tailroom;
 
 	rxqueue = __netif_get_rx_queue(current->nsproxy->net_ns->loopback_dev, 0);
 	xdp.rxq = &rxqueue->xdp_rxq;
@@ -496,8 +505,7 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
 	ret = bpf_test_run(prog, &xdp, repeat, &retval, &duration, true);
 	if (ret)
 		goto out;
-	if (xdp.data != data + XDP_PACKET_HEADROOM + NET_IP_ALIGN ||
-	    xdp.data_end != xdp.data + size)
+	if (xdp.data != data + headroom || xdp.data_end != xdp.data + size)
 		size = xdp.data_end - xdp.data;
 	ret = bpf_test_finish(kattr, uattr, xdp.data, size, retval, duration);
 out: