netdev - Re: [PATCH net-next v2] xen-netfront: add basic XDP support

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Date:   Thu, 5 Mar 2020 15:35:27 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Denis Kirjanov <kda@...ux-powerpc.org>
Cc:     brouer@...hat.com, netdev@...r.kernel.org, jgross@...e.com,
        ilias.apalodimas@...aro.org
Subject: Re: [PATCH net-next v2] xen-netfront: add basic XDP support

On Mon,  2 Mar 2020 17:21:14 +0300
Denis Kirjanov <kda@...ux-powerpc.org> wrote:

> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index 482c6c8..db8a280 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
[...]
> @@ -778,6 +782,40 @@ static int xennet_get_extras(struct netfront_queue *queue,
>  	return err;
>  }
>  
> +u32 xennet_run_xdp(struct netfront_queue *queue, struct page *pdata,
> +		   struct xen_netif_rx_response *rx, struct bpf_prog *prog,
> +		   struct xdp_buff *xdp)
> +{
> +	u32 len = rx->status;
> +	u32 act = XDP_PASS;
> +
> +	xdp->data_hard_start = page_address(pdata);
> +	xdp->data = xdp->data_hard_start + XDP_PACKET_HEADROOM;
> +	xdp_set_data_meta_invalid(xdp);
> +	xdp->data_end = xdp->data + len;
> +	xdp->handle = 0;
> +
> +	act = bpf_prog_run_xdp(prog, xdp);
> +	switch (act) {
> +	case XDP_PASS:
> +	case XDP_TX:
> +	case XDP_DROP:
> +		break;
> +
> +	case XDP_ABORTED:
> +		trace_xdp_exception(queue->info->netdev, prog, act);
> +		break;
> +
> +	default:
> +		bpf_warn_invalid_xdp_action(act);
> +	}
> +
> +	if (act != XDP_PASS && act != XDP_TX)
> +		xdp->data_hard_start = NULL;
> +
> +	return act;
> +}
> +
>  static int xennet_get_responses(struct netfront_queue *queue,
>  				struct netfront_rx_info *rinfo, RING_IDX rp,
>  				struct sk_buff_head *list)
> @@ -792,6 +830,9 @@ static int xennet_get_responses(struct netfront_queue *queue,
>  	int slots = 1;
>  	int err = 0;
>  	unsigned long ret;
> +	struct bpf_prog *xdp_prog;
> +	struct xdp_buff xdp;
> +	u32 verdict;
>  
>  	if (rx->flags & XEN_NETRXF_extra_info) {
>  		err = xennet_get_extras(queue, extras, rp);
> @@ -827,6 +868,22 @@ static int xennet_get_responses(struct netfront_queue *queue,
>  
>  		gnttab_release_grant_reference(&queue->gref_rx_head, ref);
>  
> +		rcu_read_lock();
> +		xdp_prog = rcu_dereference(queue->xdp_prog);
> +		if (xdp_prog) {
> +			/* currently only a single page contains data */
> +			WARN_ON_ONCE(skb_shinfo(skb)->nr_frags != 1);
> +			verdict = xennet_run_xdp(queue,
> +				       skb_frag_page(&skb_shinfo(skb)->frags[0]),

This looks really weird, skb_shinfo(skb)->frags[0], you already have an
SKB and you are sending fragment-0 to the xennet_run_xdp() function.

XDP meant to run before an SKB is allocated...

> +				       rx, xdp_prog, &xdp);
> +
> +			if (verdict != XDP_PASS && verdict != XDP_TX) {
> +				err = -EINVAL;
> +				goto next;
> +			}
> +
> +		}
> +		rcu_read_unlock();
>  		__skb_queue_tail(list, skb);


-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer