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Date: Thu, 16 Apr 2020 16:02:28 +0200
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org
Cc: davem@...emloft.net, kuba@...nel.org,
prashantbhole.linux@...il.com, jasowang@...hat.com,
brouer@...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>
Subject: Re: [PATCH RFC-v5 bpf-next 09/12] dev: Support xdp in the Tx path for xdp_frames
David Ahern <dsahern@...nel.org> writes:
> From: David Ahern <dahern@...italocean.com>
>
> Add support to run Tx path program on xdp_frames by adding a hook to
> bq_xmit_all before xdp_frames are passed to ndo_xdp_xmit for the device.
>
> If an xdp_frame is dropped by the program, it is removed from the
> xdp_frames array with subsequent entries moved up.
>
> Signed-off-by: David Ahern <dahern@...italocean.com>
> ---
> include/linux/netdevice.h | 3 ++
> kernel/bpf/devmap.c | 19 ++++++++---
> net/core/dev.c | 70 +++++++++++++++++++++++++++++++++++++++
> 3 files changed, 87 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 39e1b42c042f..d75e31ac2751 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -3715,6 +3715,9 @@ static inline void dev_consume_skb_any(struct sk_buff *skb)
> void generic_xdp_tx(struct sk_buff *skb, struct bpf_prog *xdp_prog);
> int do_xdp_generic_rx(struct bpf_prog *xdp_prog, struct sk_buff *skb);
> u32 do_xdp_egress_skb(struct net_device *dev, struct sk_buff *skb);
> +unsigned int do_xdp_egress_frame(struct net_device *dev,
> + struct xdp_frame **frames,
> + unsigned int *pcount);
> int netif_rx(struct sk_buff *skb);
> int netif_rx_ni(struct sk_buff *skb);
> int netif_receive_skb(struct sk_buff *skb);
> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
> index 58bdca5d978a..bedecd07d898 100644
> --- a/kernel/bpf/devmap.c
> +++ b/kernel/bpf/devmap.c
> @@ -322,24 +322,33 @@ static int bq_xmit_all(struct xdp_dev_bulk_queue *bq, u32 flags)
> {
> struct net_device *dev = bq->dev;
> int sent = 0, drops = 0, err = 0;
> + unsigned int count = bq->count;
> int i;
>
> - if (unlikely(!bq->count))
> + if (unlikely(!count))
> return 0;
>
> - for (i = 0; i < bq->count; i++) {
> + for (i = 0; i < count; i++) {
> struct xdp_frame *xdpf = bq->q[i];
>
> prefetch(xdpf);
> }
>
> - sent = dev->netdev_ops->ndo_xdp_xmit(dev, bq->count, bq->q, flags);
> + if (static_branch_unlikely(&xdp_egress_needed_key)) {
> + count = do_xdp_egress_frame(dev, bq->q, &count);
nit: seems a bit odd to pass the point to count, then reassign it with
the return value?
> + drops += bq->count - count;
> + /* all frames consumed by the xdp program? */
> + if (!count)
> + goto out;
> + }
> +
> + sent = dev->netdev_ops->ndo_xdp_xmit(dev, count, bq->q, flags);
> if (sent < 0) {
> err = sent;
> sent = 0;
> goto error;
> }
> - drops = bq->count - sent;
> + drops += count - sent;
> out:
> bq->count = 0;
>
> @@ -351,7 +360,7 @@ static int bq_xmit_all(struct xdp_dev_bulk_queue *bq, u32 flags)
> /* If ndo_xdp_xmit fails with an errno, no frames have been
> * xmit'ed and it's our responsibility to them free all.
> */
> - for (i = 0; i < bq->count; i++) {
> + for (i = 0; i < count; i++) {
> struct xdp_frame *xdpf = bq->q[i];
>
> xdp_return_frame_rx_napi(xdpf);
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 1bbaeb8842ed..f23dc6043329 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -4720,6 +4720,76 @@ u32 do_xdp_egress_skb(struct net_device *dev, struct sk_buff *skb)
> }
> EXPORT_SYMBOL_GPL(do_xdp_egress_skb);
>
> +static u32 __xdp_egress_frame(struct net_device *dev,
> + struct bpf_prog *xdp_prog,
> + struct xdp_frame *xdp_frame,
> + struct xdp_txq_info *txq)
> +{
> + struct xdp_buff xdp;
> + u32 act;
> +
> + xdp.data_hard_start = xdp_frame->data - xdp_frame->headroom;
> + xdp.data = xdp_frame->data;
> + xdp.data_end = xdp.data + xdp_frame->len;
> + xdp_set_data_meta_invalid(&xdp);
Why invalidate the metadata? On the contrary we'd want metadata from the
RX side to survive, wouldn't we?
> + xdp.txq = txq;
> +
> + act = bpf_prog_run_xdp(xdp_prog, &xdp);
> + act = handle_xdp_egress_act(act, dev, xdp_prog);
> +
> + /* if not dropping frame, readjust pointers in case
> + * program made changes to the buffer
> + */
> + if (act != XDP_DROP) {
> + int headroom = xdp.data - xdp.data_hard_start;
> + int metasize = xdp.data - xdp.data_meta;
> +
> + metasize = metasize > 0 ? metasize : 0;
> + if (unlikely((headroom - metasize) < sizeof(*xdp_frame)))
> + return XDP_DROP;
> +
> + xdp_frame = xdp.data_hard_start;
> + xdp_frame->data = xdp.data;
> + xdp_frame->len = xdp.data_end - xdp.data;
> + xdp_frame->headroom = headroom - sizeof(*xdp_frame);
> + xdp_frame->metasize = metasize;
> + /* xdp_frame->mem is unchanged */
> + }
> +
> + return act;
> +}
> +
> +unsigned int do_xdp_egress_frame(struct net_device *dev,
> + struct xdp_frame **frames,
> + unsigned int *pcount)
> +{
> + struct bpf_prog *xdp_prog;
> + unsigned int count = *pcount;
> +
> + xdp_prog = rcu_dereference(dev->xdp_egress_prog);
> + if (xdp_prog) {
> + struct xdp_txq_info txq = { .dev = dev };
Do you have any thoughts on how to populate this for the redirect case?
I guess using Magnus' HWQ abstraction when that lands? Or did you have
something different in mind?
> + unsigned int i, j;
> + u32 act;
> +
> + for (i = 0, j = 0; i < count; i++) {
> + struct xdp_frame *frame = frames[i];
> +
> + act = __xdp_egress_frame(dev, xdp_prog, frame, &txq);
> + if (act == XDP_DROP) {
> + xdp_return_frame_rx_napi(frame);
> + continue;
> + }
> +
> + frames[j] = frame;
> + j++;
> + }
> + count = j;
> + }
> +
> + return count;
> +}
> +
> static int netif_rx_internal(struct sk_buff *skb)
> {
> int ret;
> --
> 2.21.1 (Apple Git-122.3)
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