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Date: Tue, 3 Mar 2020 11:40:44 +0100
From: Jesper Dangaard Brouer <brouer@...hat.com>
To: David Ahern <dsahern@...nel.org>
Cc: netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
prashantbhole.linux@...il.com, jasowang@...hat.com,
toke@...hat.com, mst@...hat.com, toshiaki.makita1@...il.com,
daniel@...earbox.net, john.fastabend@...il.com, ast@...nel.org,
kafai@...com, songliubraving@...com, yhs@...com, andriin@...com,
dsahern@...il.com, David Ahern <dahern@...italocean.com>,
brouer@...hat.com
Subject: Re: [PATCH RFC v4 bpf-next 09/11] tun: Support xdp in the Tx path
for xdp_frames
On Wed, 26 Feb 2020 20:20:11 -0700
David Ahern <dsahern@...nel.org> wrote:
> From: David Ahern <dahern@...italocean.com>
>
> Add support to run Tx path program on packets arriving at a tun
> device via XDP redirect.
>
> XDP_TX return code means move the packet to the Tx path of the device.
> For a program run in the Tx / egress path, XDP_TX is essentially the
> same as "continue on" which is XDP_PASS.
>
> Conceptually, XDP_REDIRECT for this path can work the same as it
> does for the Rx path, but that return code is left for a follow
> on series.
>
> Signed-off-by: Prashant Bhole <prashantbhole.linux@...il.com>
> Signed-off-by: David Ahern <dahern@...italocean.com>
> ---
> drivers/net/tun.c | 49 +++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 47 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index dcae6521a39d..d3fc7e921c85 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1359,10 +1359,50 @@ static void __tun_xdp_flush_tfile(struct tun_file *tfile)
> tfile->socket.sk->sk_data_ready(tfile->socket.sk);
> }
>
> +static u32 tun_do_xdp_tx(struct tun_struct *tun, struct tun_file *tfile,
> + struct xdp_frame *frame, struct xdp_txq_info *txq)
> +{
> + struct bpf_prog *xdp_prog;
> + u32 act = XDP_PASS;
> +
> + xdp_prog = rcu_dereference(tun->xdp_egress_prog);
> + if (xdp_prog) {
> + struct xdp_buff xdp;
> +
> + xdp.data_hard_start = frame->data - frame->headroom;
This is correct, only because frame->headroom have been reduced with
sizeof(*xdp_frame), as we want to avoid that the BPF-prog have access
to xdp_frame memory. Remember that memory storing xdp_frame in located
in the top of the payload/page.
> + xdp.data = frame->data;
> + xdp.data_end = xdp.data + frame->len;
> + xdp_set_data_meta_invalid(&xdp);
> + xdp.txq = txq;
> +
> + act = bpf_prog_run_xdp(xdp_prog, &xdp);
The BPF-prog can change/adjust headroom and tailroom (tail only shrink,
but I'm working on extending this). Thus, you need to adjust the
xdp_frame accordingly afterwards.
(The main use-case is pushing on a header, right?)
> + switch (act) {
> + case XDP_TX: /* for Tx path, XDP_TX == XDP_PASS */
> + act = XDP_PASS;
> + break;
> + case XDP_PASS:
> + break;
> + case XDP_REDIRECT:
> + /* fall through */
> + default:
> + bpf_warn_invalid_xdp_action(act);
> + /* fall through */
> + case XDP_ABORTED:
> + trace_xdp_exception(tun->dev, xdp_prog, act);
> + /* fall through */
> + case XDP_DROP:
> + break;
> + }
> + }
> +
> + return act;
> +}
> +
> static int tun_xdp_xmit(struct net_device *dev, int n,
> struct xdp_frame **frames, u32 flags)
> {
> struct tun_struct *tun = netdev_priv(dev);
> + struct xdp_txq_info txq = { .dev = dev };
> struct tun_file *tfile;
> u32 numqueues;
> int drops = 0;
> @@ -1389,12 +1429,17 @@ static int tun_xdp_xmit(struct net_device *dev, int n,
> spin_lock(&tfile->tx_ring.producer_lock);
> for (i = 0; i < n; i++) {
> struct xdp_frame *xdp = frames[i];
> + void *frame;
> +
> + if (tun_do_xdp_tx(tun, tfile, xdp, &txq) != XDP_PASS)
> + goto drop;
> +
> /* Encode the XDP flag into lowest bit for consumer to differ
> * XDP buffer from sk_buff.
> */
> - void *frame = tun_xdp_to_ptr(xdp);
> -
> + frame = tun_xdp_to_ptr(xdp);
> if (__ptr_ring_produce(&tfile->tx_ring, frame)) {
> +drop:
> this_cpu_inc(tun->pcpu_stats->tx_dropped);
> xdp_return_frame_rx_napi(xdp);
> drops++;
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
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