netdev - Re: [net-next, PATCH 2/2, v1] net: socionext: add AF

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Date:   Mon, 10 Sep 2018 14:20:38 +0300
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
Cc:     netdev@...r.kernel.org, jaswinder.singh@...aro.org,
        ard.biesheuvel@...aro.org, masami.hiramatsu@...aro.org,
        arnd@...db.de, mykyta.iziumtsev@...aro.org, bjorn.topel@...el.com,
        magnus.karlsson@...el.com
Subject: Re: [net-next, PATCH 2/2, v1] net: socionext: add AF_XDP support

On Mon, Sep 10, 2018 at 07:56:49PM +0900, Toshiaki Makita wrote:
> On 2018/09/10 17:24, Ilias Apalodimas wrote:
> > Add basic AF_XDP support without zero-copy
> > 
> > Signed-off-by: Ilias Apalodimas <ilias.apalodimas@...aro.org>
> > ---
> ...
> > @@ -707,6 +731,26 @@ static int netsec_process_rx(struct netsec_priv *priv, int budget)
> >  		if (unlikely(!buf_addr))
> >  			break;
> >  
> > +		if (xdp_prog) {
> > +			xdp_result = netsec_run_xdp(desc, priv, xdp_prog,
> > +						    pkt_len);
> > +			if (xdp_result != NETSEC_XDP_PASS) {
> > +				xdp_flush |= xdp_result & NETSEC_XDP_REDIR;
> > +
> > +				dma_unmap_single_attrs(priv->dev,
> > +						       desc->dma_addr,
> > +						       desc->len, DMA_TO_DEVICE,
> > +						       DMA_ATTR_SKIP_CPU_SYNC);
> > +
> > +				desc->len = desc_len;
> > +				desc->dma_addr = dma_handle;
> > +				desc->addr = buf_addr;
> > +				netsec_rx_fill(priv, idx, 1);
> > +				nsetsec_adv_desc(&dring->tail);
> > +			}
> > +			continue;
> 
> Continue even on XDP_PASS? Is this really correct?
> 
> Also seems there is no handling of adjust_head/tail for XDP_PASS case.
No continue is wrong there, thanks for the catch. This should return the packet
to the network stack. I'll fix it on v2.

> 
> > +		}
> > +
> >  		skb = build_skb(desc->addr, desc->len);
> >  		if (unlikely(!skb)) {
> >  			dma_unmap_single(priv->dev, dma_handle, desc_len,
> > @@ -740,6 +784,9 @@ static int netsec_process_rx(struct netsec_priv *priv, int budget)
> >  		nsetsec_adv_desc(&dring->tail);
> >  	}
> >  
> > +	if (xdp_flush & NETSEC_XDP_REDIR)
> > +		xdp_do_flush_map();
> > +
> >  	return done;
> >  }
> ...
> > +static u32 netsec_run_xdp(struct netsec_desc *desc, struct netsec_priv *priv,
> > +			  struct bpf_prog *prog, u16 len)
> > +
> > +{
> > +	struct netsec_desc_ring *dring = &priv->desc_ring[NETSEC_RING_RX];
> > +	struct xdp_buff xdp;
> > +	u32 ret = NETSEC_XDP_PASS;
> > +	int err;
> > +	u32 act;
> > +
> > +	xdp.data_hard_start = desc->addr;
> > +	xdp.data = desc->addr;
> 
> There is no headroom. REDIRECT using devmap/cpumap will fail due to
> this. Generally we need XDP_PACKET_HEADROOM.
> 
Ok, i'll modify the patch to include XDP_PACKET_HEADROOM
> > +	xdp_set_data_meta_invalid(&xdp);
> > +	xdp.data_end = xdp.data + len;
> > +	xdp.rxq = &dring->xdp_rxq;
> > +
> > +	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_xmit_xdp(priv, &xdp, desc);
> > +		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;
> > +		break;
> > +	}
> > +
> > +	rcu_read_unlock();
> > +
> > +	return ret;
> > +}
> > +
> > +static int netsec_xdp_setup(struct netsec_priv *priv, struct bpf_prog *prog)
> > +{
> > +	struct net_device *dev = priv->ndev;
> > +	struct bpf_prog *old_prog;
> > +
> > +	/* For now just support only the usual MTU sized frames */
> > +	if (prog && dev->mtu > 1500) {
> > +		netdev_warn(dev, "Jumbo frames not yet supported with XDP\n");
> 
> Why not using extack?
> 
Wasn't aware that this should use the extack for errors. I just saw the same
check on an existing driver and thought that was the way to go
> > +		return -EOPNOTSUPP;
> > +	}
> > +

Thanks for having a look!

/Ilias