Subject: Re: [PATCH v3 net-next 5/8] net: mvneta: add basic XDP support

From: Lorenzo Bianconi <[email-masked]>
Date: Mon, 14 Oct 2019 15:27:04 +0200

> On Mon, 14 Oct 2019 12:49:52 +0200
> Lorenzo Bianconi <[email-masked]> wrote:
> 
> > Add basic XDP support to mvneta driver for devices that rely on software
> > buffer management. Currently supported verdicts are:
> > - XDP_DROP
> > - XDP_PASS
> > - XDP_REDIRECT
> > - XDP_ABORTED
> > 
> > - iptables drop:
> > $iptables -t raw -I PREROUTING -p udp --dport 9 -j DROP
> > $nstat -n && sleep 1 && nstat
> > IpInReceives		151169		0.0
> > IpExtInOctets		6953544		0.0
> > IpExtInNoECTPkts	151165		0.0
> > 
> > - XDP_DROP via xdp1
> > $./samples/bpf/xdp1 3
> > proto 0:	421419 pkt/s
> > proto 0:	421444 pkt/s
> > proto 0:	421393 pkt/s
> > proto 0:	421440 pkt/s
> > proto 0:	421184 pkt/s
> > 
> > Tested-by: Matteo Croce <[email-masked]>
> > Signed-off-by: Lorenzo Bianconi <[email-masked]>
> > ---
> >  drivers/net/ethernet/marvell/mvneta.c | 147 ++++++++++++++++++++++++--
> >  1 file changed, 138 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
> > index 1722dffe265d..b47a44cf9610 100644
> > --- a/drivers/net/ethernet/marvell/mvneta.c
> > +++ b/drivers/net/ethernet/marvell/mvneta.c
> > @@ -38,6 +38,7 @@
> >  #include <net/ipv6.h>
> >  #include <net/tso.h>
> >  #include <net/page_pool.h>
> > +#include <linux/bpf_trace.h>
> >  
> >  /* Registers */
> >  #define MVNETA_RXQ_CONFIG_REG(q)                (0x1400 + ((q) << 2))
> > @@ -323,8 +324,10 @@
> >  	      ETH_HLEN + ETH_FCS_LEN,			     \
> >  	      cache_line_size())
> >  
> > +#define MVNETA_SKB_HEADROOM	(max(XDP_PACKET_HEADROOM, NET_SKB_PAD) + \
> > +				 NET_IP_ALIGN)
> >  #define MVNETA_SKB_PAD	(SKB_DATA_ALIGN(sizeof(struct skb_shared_info) + \
> > -			 NET_SKB_PAD))
> > +			 MVNETA_SKB_HEADROOM))
> >  #define MVNETA_SKB_SIZE(len)	(SKB_DATA_ALIGN(len) + MVNETA_SKB_PAD)
> >  #define MVNETA_MAX_RX_BUF_SIZE	(PAGE_SIZE - MVNETA_SKB_PAD)
> >  
> > @@ -352,6 +355,11 @@ struct mvneta_statistic {
> >  #define T_REG_64	64
> >  #define T_SW		1
> >  
> > +#define MVNETA_XDP_PASS		BIT(0)
> > +#define MVNETA_XDP_CONSUMED	BIT(1)
> 
> I find it confusing that you call it "consumed" (MVNETA_XDP_CONSUMED),
> because if I follow the code these are all drop-cases that are due to
> errors.
> 
> Can we call it MVNETA_XDP_DROPPED?

Hi Jesper,

thx for the review. Sure I will rename it in v4.

Regards,
Lorenzo

> 
> I also checked, your XDP_TX patch[8/8], that all the return paths for
> MVNETA_XDP_CONSUMED also leads to drop of the xdp_buff.
> 
> 
> > +#define MVNETA_XDP_TX		BIT(2)
> > +#define MVNETA_XDP_REDIR	BIT(3)
> > +
> >  static const struct mvneta_statistic mvneta_statistics[] = {
> >  	{ 0x3000, T_REG_64, "good_octets_received", },
> >  	{ 0x3010, T_REG_32, "good_frames_received", },
> > @@ -431,6 +439,8 @@ struct mvneta_port {
> >  	u32 cause_rx_tx;
> >  	struct napi_struct napi;
> >  
> > +	struct bpf_prog *xdp_prog;
> > +
> >  	/* Core clock */
> >  	struct clk *clk;
> >  	/* AXI clock */
> > @@ -1950,11 +1960,51 @@ int mvneta_rx_refill_queue(struct mvneta_port *pp, struct mvneta_rx_queue *rxq)
> >  	return i;
> >  }
> >  
> > +static int
> > +mvneta_run_xdp(struct mvneta_port *pp, struct mvneta_rx_queue *rxq,
> > +	       struct bpf_prog *prog, struct xdp_buff *xdp)
> > +{
> > +	u32 ret, act = bpf_prog_run_xdp(prog, xdp);
> > +
> > +	switch (act) {
> > +	case XDP_PASS:
> > +		ret = MVNETA_XDP_PASS;
> > +		break;
> > +	case XDP_REDIRECT: {
> > +		int err;
> > +
> > +		err = xdp_do_redirect(pp->dev, xdp, prog);
> > +		if (err) {
> > +			ret = MVNETA_XDP_CONSUMED;
> > +			xdp_return_buff(xdp);
> 
> Dropped in case of errors.  As this is an error case, I don't mind that
> you use the slower xdp_return_buff().
> 
> 
> > +		} else {
> > +			ret = MVNETA_XDP_REDIR;
> > +		}
> > +		break;
> > +	}
> > +	default:
> > +		bpf_warn_invalid_xdp_action(act);
> > +		/* fall through */
> > +	case XDP_ABORTED:
> > +		trace_xdp_exception(pp->dev, prog, act);
> > +		/* fall through */
> > +	case XDP_DROP:
> > +		page_pool_recycle_direct(rxq->page_pool,
> > +					 virt_to_head_page(xdp->data));
> > +		ret = MVNETA_XDP_CONSUMED;
> 
> Also drop case.
> 
> > +		break;
> > +	}
> > +
> > +	return ret;
> > +}
> > +
> >  static int
> >  mvneta_swbm_rx_frame(struct mvneta_port *pp,
> >  		     struct mvneta_rx_desc *rx_desc,
> >  		     struct mvneta_rx_queue *rxq,
> > -		     struct page *page)
> > +		     struct xdp_buff *xdp,
> > +		     struct bpf_prog *xdp_prog,
> > +		     struct page *page, u32 *xdp_ret)
> >  {
> >  	unsigned char *data = page_address(page);
> >  	int data_len = -MVNETA_MH_SIZE, len;
> > @@ -1974,7 +2024,26 @@ mvneta_swbm_rx_frame(struct mvneta_port *pp,
> >  				rx_desc->buf_phys_addr,
> >  				len, dma_dir);
> >  
> > -	rxq->skb = build_skb(data, PAGE_SIZE);
> > +	xdp->data_hard_start = data;
> > +	xdp->data = data + MVNETA_SKB_HEADROOM + MVNETA_MH_SIZE;
> > +	xdp->data_end = xdp->data + data_len;
> > +	xdp_set_data_meta_invalid(xdp);
> > +
> > +	if (xdp_prog) {
> > +		u32 ret;
> > +
> > +		ret = mvneta_run_xdp(pp, rxq, xdp_prog, xdp);
> > +		if (ret != MVNETA_XDP_PASS) {
> > +			mvneta_update_stats(pp, 1,
> > +					    xdp->data_end - xdp->data,
> 
> Good, you took into account that data_len cannot be used, as BPF/XDP program could have changed data pointer, thus affecting the length.
> 
> > +					    false);
> > +			rx_desc->buf_phys_addr = 0;
> > +			*xdp_ret |= ret;
> > +			return ret;
> > +		}
> > +	}
> > +
> > +	rxq->skb = build_skb(xdp->data_hard_start, PAGE_SIZE);
> >  	if (unlikely(!rxq->skb)) {
> >  		netdev_err(dev,
> >  			   "Can't allocate skb on queue %d\n",
> > @@ -1985,8 +2054,9 @@ mvneta_swbm_rx_frame(struct mvneta_port *pp,
> >  	}
> >  	page_pool_release_page(rxq->page_pool, page);
> >  
> > -	skb_reserve(rxq->skb, MVNETA_MH_SIZE + NET_SKB_PAD);
> > -	skb_put(rxq->skb, data_len);
> > +	skb_reserve(rxq->skb,
> > +		    xdp->data - xdp->data_hard_start);
> > +	skb_put(rxq->skb, xdp->data_end - xdp->data);
> >  	mvneta_rx_csum(pp, rx_desc->status, rxq->skb);
> >  
> >  	rxq->left_size = rx_desc->data_size - len;
> > @@ -2020,7 +2090,7 @@ mvneta_swbm_add_rx_fragment(struct mvneta_port *pp,
> >  		/* refill descriptor with new buffer later */
> >  		skb_add_rx_frag(rxq->skb,
> >  				skb_shinfo(rxq->skb)->nr_frags,
> > -				page, NET_SKB_PAD, data_len,
> > +				page, MVNETA_SKB_HEADROOM, data_len,
> >  				PAGE_SIZE);
> >  	}
> >  	page_pool_release_page(rxq->page_pool, page);
> > @@ -2035,10 +2105,17 @@ static int mvneta_rx_swbm(struct napi_struct *napi,
> >  {
> >  	int rcvd_pkts = 0, rcvd_bytes = 0;
> >  	int rx_pending, refill, done = 0;
> > +	struct bpf_prog *xdp_prog;
> > +	struct xdp_buff xdp_buf;
> > +	u32 xdp_ret = 0;
> >  
> >  	/* Get number of received packets */
> >  	rx_pending = mvneta_rxq_busy_desc_num_get(pp, rxq);
> >  
> > +	rcu_read_lock();
> > +	xdp_prog = READ_ONCE(pp->xdp_prog);
> > +	xdp_buf.rxq = &rxq->xdp_rxq;
> 
> Ok, thanks for following my review comments from last.
> 
> >  	/* Fairness NAPI loop */
> >  	while (done < budget && done < rx_pending) {
> >  		struct mvneta_rx_desc *rx_desc = mvneta_rxq_next_desc_get(rxq);
> > @@ -2066,7 +2143,8 @@ static int mvneta_rx_swbm(struct napi_struct *napi,
> >  				continue;
> >  			}
> >  
> > -			err = mvneta_swbm_rx_frame(pp, rx_desc, rxq, page);
> > +			err = mvneta_swbm_rx_frame(pp, rx_desc, rxq, &xdp_buf,
> > +						   xdp_prog, page, &xdp_ret);
> >  			if (err)
> >  				continue;
> >  		} else {
> > @@ -2101,6 +2179,10 @@ static int mvneta_rx_swbm(struct napi_struct *napi,
> >  		/* clean uncomplete skb pointer in queue */
> >  		rxq->skb = NULL;
> >  	}
> > +	rcu_read_unlock();
> > +
> > +	if (xdp_ret & MVNETA_XDP_REDIR)
> > +		xdp_do_flush_map();
> >  
> >  	mvneta_update_stats(pp, rcvd_pkts, rcvd_bytes, false);
> >  
> [...]
> 
> 
> 
> -- 
> Best regards,
>   Jesper Dangaard Brouer
>   MSc.CS, Principal Kernel Engineer at Red Hat
>   LinkedIn: http://www.linkedin.com/in/brouer