RE: [PATCH net-next v3 2/7] dpaa_eth: add basic XDP support

[Camelia Alexandra Groza <camelia.groza@nxp.com>]

> -----Original Message-----
> From: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
> Sent: Friday, November 20, 2020 02:19
> To: Camelia Alexandra Groza <camelia.groza@nxp.com>
> Cc: kuba@kernel.org; brouer@redhat.com; saeed@kernel.org;
> davem@davemloft.net; Madalin Bucur (OSS)
> <madalin.bucur@oss.nxp.com>; Ioana Ciornei <ioana.ciornei@nxp.com>;
> netdev@vger.kernel.org
> Subject: Re: [PATCH net-next v3 2/7] dpaa_eth: add basic XDP support
> 
> On Thu, Nov 19, 2020 at 06:29:31PM +0200, Camelia Groza wrote:
> > Implement the XDP_DROP and XDP_PASS actions.
> >
> > Avoid draining and reconfiguring the buffer pool at each XDP
> > setup/teardown by increasing the frame headroom and reserving
> > XDP_PACKET_HEADROOM bytes from the start. Since we always reserve
> an
> > entire page per buffer, this change only impacts Jumbo frame scenarios
> > where the maximum linear frame size is reduced by 256 bytes. Multi
> > buffer Scatter/Gather frames are now used instead in these scenarios.
> >
> > Allow XDP programs to access the entire buffer.
> >
> > The data in the received frame's headroom can be overwritten by the XDP
> > program. Extract the relevant fields from the headroom while they are
> > still available, before running the XDP program.
> >
> > Since the headroom might be resized before the frame is passed up to the
> > stack, remove the check for a fixed headroom value when building an skb.
> >
> > Allow the meta data to be updated and pass the information up the stack.
> >
> > Scatter/Gather frames are dropped when XDP is enabled.
> >
> > Acked-by: Madalin Bucur <madalin.bucur@oss.nxp.com>
> > Signed-off-by: Camelia Groza <camelia.groza@nxp.com>
> > ---
> > Changes in v2:
> > - warn only once if extracting the timestamp from a received frame fails
> >
> > Changes in v3:
> > - drop received S/G frames when XDP is enabled
> >
> >  drivers/net/ethernet/freescale/dpaa/dpaa_eth.c | 158
> ++++++++++++++++++++++---
> >  drivers/net/ethernet/freescale/dpaa/dpaa_eth.h |   2 +
> >  2 files changed, 144 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> > index 88533a2..102023c 100644
> > --- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> > +++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> > @@ -53,6 +53,8 @@
> >  #include <linux/dma-mapping.h>
> >  #include <linux/sort.h>
> >  #include <linux/phy_fixed.h>
> > +#include <linux/bpf.h>
> > +#include <linux/bpf_trace.h>
> >  #include <soc/fsl/bman.h>
> >  #include <soc/fsl/qman.h>
> >  #include "fman.h"
> > @@ -177,7 +179,7 @@
> >  #define DPAA_HWA_SIZE (DPAA_PARSE_RESULTS_SIZE +
> DPAA_TIME_STAMP_SIZE \
> >  		       + DPAA_HASH_RESULTS_SIZE)
> >  #define DPAA_RX_PRIV_DATA_DEFAULT_SIZE
> (DPAA_TX_PRIV_DATA_SIZE + \
> > -					dpaa_rx_extra_headroom)
> > +					XDP_PACKET_HEADROOM -
> DPAA_HWA_SIZE)
> >  #ifdef CONFIG_DPAA_ERRATUM_A050385
> >  #define DPAA_RX_PRIV_DATA_A050385_SIZE (DPAA_A050385_ALIGN -
> DPAA_HWA_SIZE)
> >  #define DPAA_RX_PRIV_DATA_SIZE (fman_has_errata_a050385() ? \
> > @@ -1733,7 +1735,6 @@ static struct sk_buff *contig_fd_to_skb(const
> struct dpaa_priv *priv,
> >  			SKB_DATA_ALIGN(sizeof(struct skb_shared_info)));
> >  	if (WARN_ONCE(!skb, "Build skb failure on Rx\n"))
> >  		goto free_buffer;
> > -	WARN_ON(fd_off != priv->rx_headroom);
> >  	skb_reserve(skb, fd_off);
> >  	skb_put(skb, qm_fd_get_length(fd));
> >
> > @@ -2349,12 +2350,62 @@ static enum qman_cb_dqrr_result
> rx_error_dqrr(struct qman_portal *portal,
> >  	return qman_cb_dqrr_consume;
> >  }
> >
> > +static u32 dpaa_run_xdp(struct dpaa_priv *priv, struct qm_fd *fd, void
> *vaddr,
> > +			unsigned int *xdp_meta_len)
> > +{
> > +	ssize_t fd_off = qm_fd_get_offset(fd);
> > +	struct bpf_prog *xdp_prog;
> > +	struct xdp_buff xdp;
> > +	u32 xdp_act;
> > +
> > +	rcu_read_lock();
> > +
> > +	xdp_prog = READ_ONCE(priv->xdp_prog);
> > +	if (!xdp_prog) {
> > +		rcu_read_unlock();
> > +		return XDP_PASS;
> > +	}
> > +
> > +	xdp.data = vaddr + fd_off;
> 
> I feel like a little drawing of xdp_buff layout would help me with
> understanding what is going on over here :)

A region at the start of the buffer is reserved for storing hardware annotations and room for the XDP_PACKET_HEADROOM, before the actual data starts. So vaddr points to the start of the buffer, while fd offset provides the offset of the data inside the buffer. I don't feel that we are filling the xdp_buff in a majorly different way from other drivers, so please mention what is unclear here and I can provide more details.

> > +	xdp.data_meta = xdp.data;
> > +	xdp.data_hard_start = xdp.data - XDP_PACKET_HEADROOM;
> > +	xdp.data_end = xdp.data + qm_fd_get_length(fd);
> > +	xdp.frame_sz = DPAA_BP_RAW_SIZE;
> 
> Maybe you could fill xdp_buff outside of this function so that later on
> you could set xdp.rxq once per napi?

I admit I haven't looked into exactly how much performance we would gain from this, but I don't think it would be enough to justify the code churn. We don't have a clean loop for processing the received frames like I see the Intel and ENA drivers have.

> > +
> > +	xdp_act = bpf_prog_run_xdp(xdp_prog, &xdp);
> > +
> > +	/* Update the length and the offset of the FD */
> > +	qm_fd_set_contig(fd, xdp.data - vaddr, xdp.data_end - xdp.data);
> > +
> > +	switch (xdp_act) {
> > +	case XDP_PASS:
> > +		*xdp_meta_len = xdp.data - xdp.data_meta;
> > +		break;
> > +	default:
> > +		bpf_warn_invalid_xdp_action(xdp_act);
> > +		fallthrough;
> > +	case XDP_ABORTED:
> > +		trace_xdp_exception(priv->net_dev, xdp_prog, xdp_act);
> > +		fallthrough;
> > +	case XDP_DROP:
> > +		/* Free the buffer */
> > +		free_pages((unsigned long)vaddr, 0);
> > +		break;
> > +	}
> > +
> > +	rcu_read_unlock();
> > +
> > +	return xdp_act;
> > +}
> > +
> >  static enum qman_cb_dqrr_result rx_default_dqrr(struct qman_portal
> *portal,
> >  						struct qman_fq *fq,
> >  						const struct qm_dqrr_entry
> *dq,
> >  						bool sched_napi)
> >  {
> > +	bool ts_valid = false, hash_valid = false;
> >  	struct skb_shared_hwtstamps *shhwtstamps;
> > +	unsigned int skb_len, xdp_meta_len = 0;
> >  	struct rtnl_link_stats64 *percpu_stats;
> >  	struct dpaa_percpu_priv *percpu_priv;
> >  	const struct qm_fd *fd = &dq->fd;
> > @@ -2362,12 +2413,14 @@ static enum qman_cb_dqrr_result
> rx_default_dqrr(struct qman_portal *portal,
> >  	enum qm_fd_format fd_format;
> >  	struct net_device *net_dev;
> >  	u32 fd_status, hash_offset;
> > +	struct qm_sg_entry *sgt;
> >  	struct dpaa_bp *dpaa_bp;
> >  	struct dpaa_priv *priv;
> > -	unsigned int skb_len;
> >  	struct sk_buff *skb;
> >  	int *count_ptr;
> > +	u32 xdp_act;
> >  	void *vaddr;
> > +	u32 hash;
> >  	u64 ns;
> >
> >  	fd_status = be32_to_cpu(fd->status);
> > @@ -2423,35 +2476,67 @@ static enum qman_cb_dqrr_result
> rx_default_dqrr(struct qman_portal *portal,
> >  	count_ptr = this_cpu_ptr(dpaa_bp->percpu_count);
> >  	(*count_ptr)--;
> >
> > -	if (likely(fd_format == qm_fd_contig))
> > +	/* Extract the timestamp stored in the headroom before running
> XDP */
> > +	if (priv->rx_tstamp) {
> > +		if (!fman_port_get_tstamp(priv->mac_dev->port[RX], vaddr,
> &ns))
> > +			ts_valid = true;
> > +		else
> > +			WARN_ONCE(1, "fman_port_get_tstamp failed!\n");
> > +	}
> > +
> > +	/* Extract the hash stored in the headroom before running XDP */
> > +	if (net_dev->features & NETIF_F_RXHASH && priv->keygen_in_use
> &&
> > +	    !fman_port_get_hash_result_offset(priv->mac_dev->port[RX],
> > +					      &hash_offset)) {
> > +		hash = be32_to_cpu(*(u32 *)(vaddr + hash_offset));
> > +		hash_valid = true;
> > +	}
> > +
> > +	if (likely(fd_format == qm_fd_contig)) {
> > +		xdp_act = dpaa_run_xdp(priv, (struct qm_fd *)fd, vaddr,
> > +				       &xdp_meta_len);
> > +		if (xdp_act != XDP_PASS) {
> > +			percpu_stats->rx_packets++;
> > +			percpu_stats->rx_bytes += qm_fd_get_length(fd);
> > +			return qman_cb_dqrr_consume;
> > +		}
> >  		skb = contig_fd_to_skb(priv, fd);
> > -	else
> > +	} else {
> > +		/* XDP doesn't support S/G frames. Return the fragments to
> the
> > +		 * buffer pool and release the SGT.
> > +		 */
> > +		if (READ_ONCE(priv->xdp_prog)) {
> > +			WARN_ONCE(1, "S/G frames not supported under
> XDP\n");
> > +			sgt = vaddr + qm_fd_get_offset(fd);
> > +			dpaa_release_sgt_members(sgt);
> > +			free_pages((unsigned long)vaddr, 0);
> > +			return qman_cb_dqrr_consume;
> > +		}
> >  		skb = sg_fd_to_skb(priv, fd);
> > +	}
> >  	if (!skb)
> >  		return qman_cb_dqrr_consume;
> >
> > -	if (priv->rx_tstamp) {
> > +	if (xdp_meta_len)
> > +		skb_metadata_set(skb, xdp_meta_len);
> 
> This is working on a single buffer, right? So there's no need to clear
> xdp_meta_len?

I don't think I understand what you mean. Are you saying I shouldn't be initializing xdp_meta_len to 0? This receive path is used when XDP is disabled as well, in which case we don't propagate the metadata.

> > +
> > +	/* Set the previously extracted timestamp */
> > +	if (ts_valid) {
> >  		shhwtstamps = skb_hwtstamps(skb);
> >  		memset(shhwtstamps, 0, sizeof(*shhwtstamps));
> > -
> > -		if (!fman_port_get_tstamp(priv->mac_dev->port[RX], vaddr,
> &ns))
> > -			shhwtstamps->hwtstamp = ns_to_ktime(ns);
> > -		else
> > -			dev_warn(net_dev->dev.parent,
> "fman_port_get_tstamp failed!\n");
> > +		shhwtstamps->hwtstamp = ns_to_ktime(ns);
> >  	}
> >
> >  	skb->protocol = eth_type_trans(skb, net_dev);
> >
> > -	if (net_dev->features & NETIF_F_RXHASH && priv->keygen_in_use
> &&
> > -	    !fman_port_get_hash_result_offset(priv->mac_dev->port[RX],
> > -					      &hash_offset)) {
> > +	/* Set the previously extracted hash */
> > +	if (hash_valid) {
> >  		enum pkt_hash_types type;
> >
> >  		/* if L4 exists, it was used in the hash generation */
> >  		type = be32_to_cpu(fd->status) & FM_FD_STAT_L4CV ?
> >  			PKT_HASH_TYPE_L4 : PKT_HASH_TYPE_L3;
> > -		skb_set_hash(skb, be32_to_cpu(*(u32 *)(vaddr +
> hash_offset)),
> > -			     type);
> > +		skb_set_hash(skb, hash, type);
> >  	}
> >
> >  	skb_len = skb->len;
> > @@ -2671,6 +2756,46 @@ static int dpaa_eth_stop(struct net_device
> *net_dev)
> >  	return err;
> >  }
> >
> > +static int dpaa_setup_xdp(struct net_device *net_dev, struct bpf_prog
> *prog)
> > +{
> > +	struct dpaa_priv *priv = netdev_priv(net_dev);
> > +	struct bpf_prog *old_prog;
> > +	bool up;
> > +	int err;
> > +
> > +	/* S/G fragments are not supported in XDP-mode */
> > +	if (prog && (priv->dpaa_bp->raw_size <
> > +	    net_dev->mtu + VLAN_ETH_HLEN + ETH_FCS_LEN))
> > +		return -EINVAL;
> 
> Don't you want to include extack message here?

This code is moved in the third patch and a dev_warn() is added. I should have added the warning from the start. I'll update it in the next version.

> > +
> > +	up = netif_running(net_dev);
> > +
> > +	if (up)
> > +		dpaa_eth_stop(net_dev);
> > +
> > +	old_prog = xchg(&priv->xdp_prog, prog);
> > +	if (old_prog)
> > +		bpf_prog_put(old_prog);
> > +
> > +	if (up) {
> > +		err = dpaa_open(net_dev);
> > +		if (err)
> > +			return err;
> 
> Out of curiosity, what should user do for that case? Would he be aware of
> the weird state of interface?

This is an improbable state to reach. An error message would be useful. I'll add it in the next version. Thanks.

> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static int dpaa_xdp(struct net_device *net_dev, struct netdev_bpf *xdp)
> > +{
> > +	switch (xdp->command) {
> > +	case XDP_SETUP_PROG:
> > +		return dpaa_setup_xdp(net_dev, xdp->prog);
> > +	default:
> > +		return -EINVAL;
> > +	}
> > +}
> > +
> >  static int dpaa_ts_ioctl(struct net_device *dev, struct ifreq *rq, int cmd)
> >  {
> >  	struct dpaa_priv *priv = netdev_priv(dev);
> > @@ -2737,6 +2862,7 @@ static int dpaa_ioctl(struct net_device *net_dev,
> struct ifreq *rq, int cmd)
> >  	.ndo_set_rx_mode = dpaa_set_rx_mode,
> >  	.ndo_do_ioctl = dpaa_ioctl,
> >  	.ndo_setup_tc = dpaa_setup_tc,
> > +	.ndo_bpf = dpaa_xdp,
> >  };
> >
> >  static int dpaa_napi_add(struct net_device *net_dev)
> > diff --git a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.h
> b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.h
> > index da30e5d..94e8613 100644
> > --- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.h
> > +++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.h
> > @@ -196,6 +196,8 @@ struct dpaa_priv {
> >
> >  	bool tx_tstamp; /* Tx timestamping enabled */
> >  	bool rx_tstamp; /* Rx timestamping enabled */
> > +
> > +	struct bpf_prog *xdp_prog;
> >  };
> >
> >  /* from dpaa_ethtool.c */
> > --
> > 1.9.1
> >