Subject: Re: [RFC, PATCH 2/2, net-next] net: netsec: add XDP support

From: Ilias Apalodimas <[email-masked]>
Date: Fri, 28 Jun 2019 09:54:12 +0300

Hi Maciej Fijalkowski,

[...]
> > +	tx_ctrl.cksum_offload_flag = false;
> > +	tx_ctrl.tcp_seg_offload_flag = false;
> > +	tx_ctrl.tcp_seg_len = 0;
> 
> Aren't these three lines redundant? tx_ctrl is zero initialized.
> 
Yea i think i can remove those

> > +
> > +	tx_desc.dma_addr = dma_handle;
> > +	tx_desc.addr = xdpf->data;
> > +	tx_desc.len = xdpf->len;
> > +
> > +	netsec_set_tx_de(priv, tx_ring, &tx_ctrl, &tx_desc, xdpf);
> > +
> > +	return NETSEC_XDP_TX;
> > +}
> > +
> > +static u32 netsec_xdp_xmit_back(struct netsec_priv *priv, struct xdp_buff *xdp)
> > +{
> > +	struct netsec_desc_ring *tx_ring = &priv->desc_ring[NETSEC_RING_TX];
> > +	struct xdp_frame *xdpf = convert_to_xdp_frame(xdp);
> > +	u32 ret;
> > +
> > +	if (unlikely(!xdpf))
> > +		return NETSEC_XDP_CONSUMED;
> > +
> > +	spin_lock(&tx_ring->lock);
> > +	ret = netsec_xdp_queue_one(priv, xdpf, false);
> > +	spin_unlock(&tx_ring->lock);
> > +
> > +	return ret;
> > +}
> > +
> > +static u32 netsec_run_xdp(struct netsec_priv *priv, struct bpf_prog *prog,
> > +			  struct xdp_buff *xdp)
> > +{
> > +	u32 ret = NETSEC_XDP_PASS;
> > +	int err;
> > +	u32 act;
> > +
> > +	rcu_read_lock();
> > +	act = bpf_prog_run_xdp(prog, xdp);
> > +
> > +	switch (act) {
> > +	case XDP_PASS:
> > +		ret = NETSEC_XDP_PASS;
> > +		break;
> > +	case XDP_TX:
> > +		ret = netsec_xdp_xmit_back(priv, xdp);
> > +		if (ret != NETSEC_XDP_TX)
> > +			xdp_return_buff(xdp);
> > +		break;
> > +	case XDP_REDIRECT:
> > +		err = xdp_do_redirect(priv->ndev, xdp, prog);
> > +		if (!err) {
> > +			ret = NETSEC_XDP_REDIR;
> > +		} else {
> > +			ret = NETSEC_XDP_CONSUMED;
> > +			xdp_return_buff(xdp);
> > +		}
> > +		break;
> > +	default:
> > +		bpf_warn_invalid_xdp_action(act);
> > +		/* fall through */
> > +	case XDP_ABORTED:
> > +		trace_xdp_exception(priv->ndev, prog, act);
> > +		/* fall through -- handle aborts by dropping packet */
> > +	case XDP_DROP:
> > +		ret = NETSEC_XDP_CONSUMED;
> > +		xdp_return_buff(xdp);
> > +		break;
> > +	}
> > +
> > +	rcu_read_unlock();
> > +
> > +	return ret;
> > +}
> > +
> >  static int netsec_process_rx(struct netsec_priv *priv, int budget)
> >  {
> >  	struct netsec_desc_ring *dring = &priv->desc_ring[NETSEC_RING_RX];
> > +	struct bpf_prog *xdp_prog = READ_ONCE(priv->xdp_prog);
> 
> Reading BPF prog should be RCU protected. There might be a case where RCU
> callback that destroys BPF prog is executed during the bottom half handling and
> you have the PREEMPT_RCU=y in your kernel config. I've just rephrased Brenden's
> words here, so for further info, see:
> 
> https://lore.kernel.org/netdev/[email-masked]/
> 
> So either expand the RCU section or read prog pointer per each frame, under the
> lock, as it seems that currently we have these two schemes in drivers that
> support XDP.
> 
Thanks, i'll fix it

Cheers
/Ilias