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Date:   Mon, 11 May 2020 20:27:35 +0300
From:   Denis Kirjanov <kda@...ux-powerpc.org>
To:     Jürgen Groß <jgross@...e.com>, paul@....org
Cc:     netdev@...r.kernel.org, brouer@...hat.com, wei.liu@...nel.org,
        ilias.apalodimas@...aro.org
Subject: Re: [PATCH net-next v9 1/2] xen networking: add basic XDP support for xen-netfront

On 5/11/20, Jürgen Groß <jgross@...e.com> wrote:
> On 11.05.20 12:22, Denis Kirjanov wrote:
>> The patch adds a basic XDP processing to xen-netfront driver.
>>
>> We ran an XDP program for an RX response received from netback
>> driver. Also we request xen-netback to adjust data offset for
>> bpf_xdp_adjust_head() header space for custom headers.
>>
>> synchronization between frontend and backend parts is done
>> by using xenbus state switching:
>> Reconfiguring -> Reconfigured- > Connected
>>
>> UDP packets drop rate using xdp program is around 310 kpps
>> using ./pktgen_sample04_many_flows.sh and 160 kpps without the patch.
>
> I'm still not seeing proper synchronization between frontend and
> backend when an XDP program is activated.
>
> Consider the following:
>
> 1. XDP program is not active, so RX responses have no XDP headroom
> 2. netback has pushed one (or more) RX responses to the ring page
> 3. XDP program is being activated -> Reconfiguring
> 4. netback acknowledges, will add XDP headroom for following RX
>     responses
> 5. netfront reads RX response (2.) without XDP headroom from ring page
> 6. boom!

One thing that could be easily done is to set the offset on  xen-netback side
in  xenvif_rx_data_slot().  Are you okay with that?

If P

> Juergen
>
>>
>> Signed-off-by: Denis Kirjanov <denis.kirjanov@...e.com>
>> ---
>>   drivers/net/Kconfig        |   1 +
>>   drivers/net/xen-netfront.c | 317
>> ++++++++++++++++++++++++++++++++++++++++++++-
>>   2 files changed, 312 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
>> index 25a8f93..45918ce 100644
>> --- a/drivers/net/Kconfig
>> +++ b/drivers/net/Kconfig
>> @@ -479,6 +479,7 @@ config XEN_NETDEV_FRONTEND
>>   	tristate "Xen network device frontend driver"
>>   	depends on XEN
>>   	select XEN_XENBUS_FRONTEND
>> +	select PAGE_POOL
>>   	default y
>>   	help
>>   	  This driver provides support for Xen paravirtual network
>> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
>> index 482c6c8..33544c7 100644
>> --- a/drivers/net/xen-netfront.c
>> +++ b/drivers/net/xen-netfront.c
>> @@ -44,6 +44,9 @@
>>   #include <linux/mm.h>
>>   #include <linux/slab.h>
>>   #include <net/ip.h>
>> +#include <linux/bpf.h>
>> +#include <net/page_pool.h>
>> +#include <linux/bpf_trace.h>
>>
>>   #include <xen/xen.h>
>>   #include <xen/xenbus.h>
>> @@ -102,6 +105,8 @@ struct netfront_queue {
>>   	char name[QUEUE_NAME_SIZE]; /* DEVNAME-qN */
>>   	struct netfront_info *info;
>>
>> +	struct bpf_prog __rcu *xdp_prog;
>> +
>>   	struct napi_struct napi;
>>
>>   	/* Split event channels support, tx_* == rx_* when using
>> @@ -144,6 +149,9 @@ struct netfront_queue {
>>   	struct sk_buff *rx_skbs[NET_RX_RING_SIZE];
>>   	grant_ref_t gref_rx_head;
>>   	grant_ref_t grant_rx_ref[NET_RX_RING_SIZE];
>> +
>> +	struct page_pool *page_pool;
>> +	struct xdp_rxq_info xdp_rxq;
>>   };
>>
>>   struct netfront_info {
>> @@ -159,6 +167,10 @@ struct netfront_info {
>>   	struct netfront_stats __percpu *rx_stats;
>>   	struct netfront_stats __percpu *tx_stats;
>>
>> +	/* XDP state */
>> +	bool netback_has_xdp_headroom;
>> +	bool netfront_xdp_enabled;
>> +
>>   	atomic_t rx_gso_checksum_fixup;
>>   };
>>
>> @@ -265,8 +277,8 @@ static struct sk_buff
>> *xennet_alloc_one_rx_buffer(struct netfront_queue *queue)
>>   	if (unlikely(!skb))
>>   		return NULL;
>>
>> -	page = alloc_page(GFP_ATOMIC | __GFP_NOWARN);
>> -	if (!page) {
>> +	page = page_pool_dev_alloc_pages(queue->page_pool);
>> +	if (unlikely(!page)) {
>>   		kfree_skb(skb);
>>   		return NULL;
>>   	}
>> @@ -560,6 +572,64 @@ static u16 xennet_select_queue(struct net_device
>> *dev, struct sk_buff *skb,
>>   	return queue_idx;
>>   }
>>
>> +static int xennet_xdp_xmit_one(struct net_device *dev, struct xdp_frame
>> *xdpf)
>> +{
>> +	struct netfront_info *np = netdev_priv(dev);
>> +	struct netfront_stats *tx_stats = this_cpu_ptr(np->tx_stats);
>> +	struct netfront_queue *queue = NULL;
>> +	unsigned int num_queues = dev->real_num_tx_queues;
>> +	unsigned long flags;
>> +	int notify;
>> +	struct xen_netif_tx_request *tx;
>> +
>> +	queue = &np->queues[smp_processor_id() % num_queues];
>> +
>> +	spin_lock_irqsave(&queue->tx_lock, flags);
>> +
>> +	tx = xennet_make_first_txreq(queue, NULL,
>> +				     virt_to_page(xdpf->data),
>> +				     offset_in_page(xdpf->data),
>> +				     xdpf->len);
>> +
>> +	RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&queue->tx, notify);
>> +	if (notify)
>> +		notify_remote_via_irq(queue->tx_irq);
>> +
>> +	u64_stats_update_begin(&tx_stats->syncp);
>> +	tx_stats->bytes += xdpf->len;
>> +	tx_stats->packets++;
>> +	u64_stats_update_end(&tx_stats->syncp);
>> +
>> +	xennet_tx_buf_gc(queue);
>> +
>> +	spin_unlock_irqrestore(&queue->tx_lock, flags);
>> +	return 0;
>> +}
>> +
>> +static int xennet_xdp_xmit(struct net_device *dev, int n,
>> +			   struct xdp_frame **frames, u32 flags)
>> +{
>> +	int drops = 0;
>> +	int i, err;
>> +
>> +	if (unlikely(flags & ~XDP_XMIT_FLAGS_MASK))
>> +		return -EINVAL;
>> +
>> +	for (i = 0; i < n; i++) {
>> +		struct xdp_frame *xdpf = frames[i];
>> +
>> +		if (!xdpf)
>> +			continue;
>> +		err = xennet_xdp_xmit_one(dev, xdpf);
>> +		if (err) {
>> +			xdp_return_frame_rx_napi(xdpf);
>> +			drops++;
>> +		}
>> +	}
>> +
>> +	return n - drops;
>> +}
>> +
>>   #define MAX_XEN_SKB_FRAGS (65536 / XEN_PAGE_SIZE + 1)
>>
>>   static netdev_tx_t xennet_start_xmit(struct sk_buff *skb, struct
>> net_device *dev)
>> @@ -778,9 +848,56 @@ static int xennet_get_extras(struct netfront_queue
>> *queue,
>>   	return err;
>>   }
>>
>> +static 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, bool *need_xdp_flush)
>> +{
>> +	struct xdp_frame *xdpf;
>> +	u32 len = rx->status;
>> +	u32 act = XDP_PASS;
>> +	int err;
>> +
>> +	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->rxq = &queue->xdp_rxq;
>> +
>> +	act = bpf_prog_run_xdp(prog, xdp);
>> +	switch (act) {
>> +	case XDP_TX:
>> +		get_page(pdata);
>> +		xdpf = convert_to_xdp_frame(xdp);
>> +		err = xennet_xdp_xmit(queue->info->netdev, 1, &xdpf, 0);
>> +		if (unlikely(err < 0))
>> +			trace_xdp_exception(queue->info->netdev, prog, act);
>> +		break;
>> +	case XDP_REDIRECT:
>> +		get_page(pdata);
>> +		err = xdp_do_redirect(queue->info->netdev, xdp, prog);
>> +		*need_xdp_flush = true;
>> +		if (unlikely(err))
>> +			trace_xdp_exception(queue->info->netdev, prog, act);
>> +		break;
>> +	case XDP_PASS:
>> +	case XDP_DROP:
>> +		break;
>> +
>> +	case XDP_ABORTED:
>> +		trace_xdp_exception(queue->info->netdev, prog, act);
>> +		break;
>> +
>> +	default:
>> +		bpf_warn_invalid_xdp_action(act);
>> +	}
>> +
>> +	return act;
>> +}
>> +
>>   static int xennet_get_responses(struct netfront_queue *queue,
>>   				struct netfront_rx_info *rinfo, RING_IDX rp,
>> -				struct sk_buff_head *list)
>> +				struct sk_buff_head *list,
>> +				bool *need_xdp_flush)
>>   {
>>   	struct xen_netif_rx_response *rx = &rinfo->rx;
>>   	struct xen_netif_extra_info *extras = rinfo->extras;
>> @@ -792,6 +909,9 @@ 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);
>> @@ -827,9 +947,24 @@ static int xennet_get_responses(struct netfront_queue
>> *queue,
>>
>>   		gnttab_release_grant_reference(&queue->gref_rx_head, ref);
>>
>> -		__skb_queue_tail(list, skb);
>> -
>> +		rcu_read_lock();
>> +		xdp_prog = rcu_dereference(queue->xdp_prog);
>> +		if (xdp_prog) {
>> +			if (!(rx->flags & XEN_NETRXF_more_data)) {
>> +				/* currently only a single page contains data */
>> +				verdict = xennet_run_xdp(queue,
>> +							 skb_frag_page(&skb_shinfo(skb)->frags[0]),
>> +							 rx, xdp_prog, &xdp, need_xdp_flush);
>> +				if (verdict != XDP_PASS)
>> +					err = -EINVAL;
>> +			} else {
>> +				/* drop the frame */
>> +				err = -EINVAL;
>> +			}
>> +		}
>> +		rcu_read_unlock();
>>   next:
>> +		__skb_queue_tail(list, skb);
>>   		if (!(rx->flags & XEN_NETRXF_more_data))
>>   			break;
>>
>> @@ -997,7 +1132,9 @@ static int xennet_poll(struct napi_struct *napi, int
>> budget)
>>   	struct sk_buff_head rxq;
>>   	struct sk_buff_head errq;
>>   	struct sk_buff_head tmpq;
>> +	struct bpf_prog *xdp_prog;
>>   	int err;
>> +	bool need_xdp_flush = false;
>>
>>   	spin_lock(&queue->rx_lock);
>>
>> @@ -1010,11 +1147,17 @@ static int xennet_poll(struct napi_struct *napi,
>> int budget)
>>
>>   	i = queue->rx.rsp_cons;
>>   	work_done = 0;
>> +	rcu_read_lock();
>>   	while ((i != rp) && (work_done < budget)) {
>>   		memcpy(rx, RING_GET_RESPONSE(&queue->rx, i), sizeof(*rx));
>>   		memset(extras, 0, sizeof(rinfo.extras));
>>
>> -		err = xennet_get_responses(queue, &rinfo, rp, &tmpq);
>> +		xdp_prog = rcu_dereference(queue->xdp_prog);
>> +		if (xdp_prog)
>> +			rx->offset = XDP_PACKET_HEADROOM;
>> +
>> +		err = xennet_get_responses(queue, &rinfo, rp, &tmpq,
>> +					   &need_xdp_flush);
>>
>>   		if (unlikely(err)) {
>>   err:
>> @@ -1060,6 +1203,9 @@ static int xennet_poll(struct napi_struct *napi, int
>> budget)
>>   		i = ++queue->rx.rsp_cons;
>>   		work_done++;
>>   	}
>> +	if (need_xdp_flush)
>> +		xdp_do_flush();
>> +	rcu_read_unlock();
>>
>>   	__skb_queue_purge(&errq);
>>
>> @@ -1261,6 +1407,98 @@ 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)
>> +{
>> +	int err;
>> +
>> +	err = xenbus_printf(XBT_NIL, np->xbdev->nodename,
>> +			    "feature-xdp", "%u", xdp);
>> +	if (err)
>> +		pr_debug("Error writing feature-xdp\n");
>> +
>> +	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;
>> +	unsigned long max_mtu = XEN_PAGE_SIZE - XDP_PACKET_HEADROOM;
>> +
>> +	if (dev->mtu > max_mtu) {
>> +		netdev_warn(dev, "XDP requires MTU less than %lu\n", max_mtu);
>> +		return -EINVAL;
>> +	}
>> +
>> +	if (!np->netback_has_xdp_headroom)
>> +		return 0;
>> +
>> +	xenbus_switch_state(np->xbdev, XenbusStateReconfiguring);
>> +
>> +	err = talk_to_netback_xdp(np, prog ? NETBACK_XDP_HEADROOM_ENABLE :
>> +				  NETBACK_XDP_HEADROOM_DISABLE);
>> +	if (err)
>> +		return err;
>> +
>> +	/* avoid race with XDP headroom adjustment */
>> +	wait_event(module_wq,
>> +		   xenbus_read_driver_state(np->xbdev->otherend) ==
>> +		   XenbusStateReconfigured);
>> +	np->netfront_xdp_enabled = true;
>> +
>> +	old_prog = rtnl_dereference(np->queues[0].xdp_prog);
>> +
>> +	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);
>> +
>> +	xenbus_switch_state(np->xbdev, XenbusStateConnected);
>> +
>> +	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 +1510,8 @@ 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,
>> +	.ndo_xdp_xmit	    = xennet_xdp_xmit,
>>   #ifdef CONFIG_NET_POLL_CONTROLLER
>>   	.ndo_poll_controller = xennet_poll_controller,
>>   #endif
>> @@ -1331,6 +1571,7 @@ static struct net_device *xennet_create_dev(struct
>> xenbus_device *dev)
>>   	SET_NETDEV_DEV(netdev, &dev->dev);
>>
>>   	np->netdev = netdev;
>> +	np->netfront_xdp_enabled = false;
>>
>>   	netif_carrier_off(netdev);
>>
>> @@ -1419,6 +1660,8 @@ static void xennet_disconnect_backend(struct
>> netfront_info *info)
>>   		queue->rx_ring_ref = GRANT_INVALID_REF;
>>   		queue->tx.sring = NULL;
>>   		queue->rx.sring = NULL;
>> +
>> +		page_pool_destroy(queue->page_pool);
>>   	}
>>   }
>>
>> @@ -1754,6 +1997,49 @@ static void xennet_destroy_queues(struct
>> netfront_info *info)
>>   	info->queues = NULL;
>>   }
>>
>> +static int xennet_create_page_pool(struct netfront_queue *queue)
>> +{
>> +	int err;
>> +	struct page_pool_params pp_params = {
>> +		.order = 0,
>> +		.flags = 0,
>> +		.pool_size = NET_RX_RING_SIZE,
>> +		.nid = NUMA_NO_NODE,
>> +		.dev = &queue->info->netdev->dev,
>> +		.offset = XDP_PACKET_HEADROOM,
>> +		.max_len = XEN_PAGE_SIZE - XDP_PACKET_HEADROOM,
>> +	};
>> +
>> +	queue->page_pool = page_pool_create(&pp_params);
>> +	if (IS_ERR(queue->page_pool)) {
>> +		err = PTR_ERR(queue->page_pool);
>> +		queue->page_pool = NULL;
>> +		return err;
>> +	}
>> +
>> +	err = xdp_rxq_info_reg(&queue->xdp_rxq, queue->info->netdev,
>> +			       queue->id);
>> +	if (err) {
>> +		netdev_err(queue->info->netdev, "xdp_rxq_info_reg failed\n");
>> +		goto err_free_pp;
>> +	}
>> +
>> +	err = xdp_rxq_info_reg_mem_model(&queue->xdp_rxq,
>> +					 MEM_TYPE_PAGE_POOL, queue->page_pool);
>> +	if (err) {
>> +		netdev_err(queue->info->netdev, "xdp_rxq_info_reg_mem_model
>> failed\n");
>> +		goto err_unregister_rxq;
>> +	}
>> +	return 0;
>> +
>> +err_unregister_rxq:
>> +	xdp_rxq_info_unreg(&queue->xdp_rxq);
>> +err_free_pp:
>> +	page_pool_destroy(queue->page_pool);
>> +	queue->page_pool = NULL;
>> +	return err;
>> +}
>> +
>>   static int xennet_create_queues(struct netfront_info *info,
>>   				unsigned int *num_queues)
>>   {
>> @@ -1779,6 +2065,14 @@ static int xennet_create_queues(struct
>> netfront_info *info,
>>   			break;
>>   		}
>>
>> +		/* use page pool recycling instead of buddy allocator */
>> +		ret = xennet_create_page_pool(queue);
>> +		if (ret < 0) {
>> +			dev_err(&info->xbdev->dev, "can't allocate page pool\n");
>> +			*num_queues = i;
>> +			return ret;
>> +		}
>> +
>>   		netif_napi_add(queue->info->netdev, &queue->napi,
>>   			       xennet_poll, 64);
>>   		if (netif_running(info->netdev))
>> @@ -1825,6 +2119,15 @@ static int talk_to_netback(struct xenbus_device
>> *dev,
>>   		goto out_unlocked;
>>   	}
>>
>> +	info->netback_has_xdp_headroom =
>> xenbus_read_unsigned(info->xbdev->otherend,
>> +							      "feature-xdp-headroom", 0);
>> +	/* set the current xen-netfront xdp state */
>> +	err = talk_to_netback_xdp(info, info->netfront_xdp_enabled ?
>> +				  NETBACK_XDP_HEADROOM_ENABLE :
>> +				  NETBACK_XDP_HEADROOM_DISABLE);
>> +	if (err)
>> +		goto out_unlocked;
>> +
>>   	rtnl_lock();
>>   	if (info->queues)
>>   		xennet_destroy_queues(info);
>> @@ -1959,6 +2262,8 @@ static int xennet_connect(struct net_device *dev)
>>   	err = talk_to_netback(np->xbdev, np);
>>   	if (err)
>>   		return err;
>> +	if (np->netback_has_xdp_headroom)
>> +		pr_info("backend supports XDP headroom\n");
>>
>>   	/* talk_to_netback() sets the correct number of queues */
>>   	num_queues = dev->real_num_tx_queues;
>>
>
>

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