Date:   Thu, 5 Mar 2020 16:23:31 +0300
From:   Denis Kirjanov <kirjanov@...il.com>
To:     Ilias Apalodimas <ilias.apalodimas@...aro.org>
Cc:     Denis Kirjanov <kda@...ux-powerpc.org>, netdev@...r.kernel.org,
        jgross@...e.com
Subject: Re: [PATCH net-next v2] xen-netfront: add basic XDP support

On 3/5/20, Ilias Apalodimas <ilias.apalodimas@...aro.org> wrote:
> Hi Denis,
>
> There's a bunch of things still missing from my remarks on V1.
> XDP is not supposed to allocate and free pages constantly as that's one of
> the
> things that's making it fast.

Hi Ilias,

I've removed the copying to an allocated page so there is no page
allocation/free logic added.


>
> You are also missing proper support for XDP_REDIRECT, ndo_xdp_xmit. We
> usually
> require the whole functionality to merge the driver.

I wanted to minimize changes and send follow-up patches

>
>
> On Mon, Mar 02, 2020 at 05:21:14PM +0300, Denis Kirjanov wrote:
>>
> [...]
>> +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:
>
> Maybe i am missing something on the usage, but XDP_TX and XDROP are handled
> similarly?
> XDP_TX is supposed to sent the packet out of the interface it arrived.

Yep, you're right. I'll add it to the next version.

Thanks!

>
>> +		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]),
>> +				       rx, xdp_prog, &xdp);
>> +
>> +			if (verdict != XDP_PASS && verdict != XDP_TX) {
>> +				err = -EINVAL;
>> +				goto next;
>> +			}
>> +
>> +		}
>> +		rcu_read_unlock();
>>  		__skb_queue_tail(list, skb);
>>
>>  next:
>> @@ -1261,6 +1318,105 @@ static void xennet_poll_controller(struct
>> net_device *dev)
>>  }
>>  #endif
>>
>> +#define NETBACK_XDP_HEADROOM_DISABLE	0
>> +#define NETBACK_XDP_HEADROOM_ENABLE	1
>> +
>> +static int talk_to_netback_xdp(struct netfront_info *np, int xdp)
>> +{
>> +	struct xenbus_transaction xbt;
>> +	const char *message;
>> +	int err;
>> +
>> +again:
>> +	err = xenbus_transaction_start(&xbt);
>> +	if (err) {
>> +		xenbus_dev_fatal(np->xbdev, err, "starting transaction");
>> +		goto out;
>> +	}
>> +
>> +	err = xenbus_printf(xbt, np->xbdev->nodename, "feature-xdp", "%d",
>> xdp);
>> +	if (err) {
>> +		message = "writing feature-xdp";
>> +		goto abort_transaction;
>> +	}
>> +
>> +	err = xenbus_transaction_end(xbt, 0);
>> +	if (err) {
>> +		if (err == -EAGAIN)
>> +			goto again;
>> +	}
>> +
>> +	return 0;
>> +
>> +abort_transaction:
>> +	xenbus_dev_fatal(np->xbdev, err, "%s", message);
>> +	xenbus_transaction_end(xbt, 1);
>> +out:
>> +	return err;
>> +}
>> +
>> +static int xennet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
>> +			struct netlink_ext_ack *extack)
>> +{
>> +	struct netfront_info *np = netdev_priv(dev);
>> +	struct bpf_prog *old_prog;
>> +	unsigned int i, err;
>> +
>> +	old_prog = rtnl_dereference(np->queues[0].xdp_prog);
>> +	if (!old_prog && !prog)
>> +		return 0;
>> +
>> +	if (prog)
>> +		bpf_prog_add(prog, dev->real_num_tx_queues);
>> +
>> +	for (i = 0; i < dev->real_num_tx_queues; ++i)
>> +		rcu_assign_pointer(np->queues[i].xdp_prog, prog);
>> +
>> +	if (old_prog)
>> +		for (i = 0; i < dev->real_num_tx_queues; ++i)
>> +			bpf_prog_put(old_prog);
>> +
>> +	err = talk_to_netback_xdp(np, old_prog ? NETBACK_XDP_HEADROOM_DISABLE:
>> +				  NETBACK_XDP_HEADROOM_ENABLE);
>> +	if (err)
>> +		return err;
>> +
>> +	xenbus_switch_state(np->xbdev, XenbusStateReconfiguring);
>> +
>> +	return 0;
>> +}
>> +
>> +static u32 xennet_xdp_query(struct net_device *dev)
>> +{
>> +	struct netfront_info *np = netdev_priv(dev);
>> +	unsigned int num_queues = dev->real_num_tx_queues;
>> +	unsigned int i;
>> +	struct netfront_queue *queue;
>> +	const struct bpf_prog *xdp_prog;
>> +
>> +	for (i = 0; i < num_queues; ++i) {
>> +		queue = &np->queues[i];
>> +		xdp_prog = rtnl_dereference(queue->xdp_prog);
>> +		if (xdp_prog)
>> +			return xdp_prog->aux->id;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static int xennet_xdp(struct net_device *dev, struct netdev_bpf *xdp)
>> +{
>> +	switch (xdp->command) {
>> +	case XDP_SETUP_PROG:
>> +		return xennet_xdp_set(dev, xdp->prog, xdp->extack);
>> +	case XDP_QUERY_PROG:
>> +		xdp->prog_id = xennet_xdp_query(dev);
>> +		return 0;
>> +	default:
>> +		return -EINVAL;
>> +	}
>> +}
>> +
>>  static const struct net_device_ops xennet_netdev_ops = {
>>  	.ndo_open            = xennet_open,
>>  	.ndo_stop            = xennet_close,
>> @@ -1272,6 +1428,7 @@ static void xennet_poll_controller(struct net_device
>> *dev)
>>  	.ndo_fix_features    = xennet_fix_features,
>>  	.ndo_set_features    = xennet_set_features,
>>  	.ndo_select_queue    = xennet_select_queue,
>> +	.ndo_bpf            = xennet_xdp,
>>  #ifdef CONFIG_NET_POLL_CONTROLLER
>>  	.ndo_poll_controller = xennet_poll_controller,
>>  #endif
>> --
>> 1.8.3.1
>>
> Cheers
> /Ilias
>


-- 
Regards / Mit besten Grüßen,
Denis

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