Subject: [PATCH net-next v9 1/2] xen networking: add basic XDP support for xen-netfront

From: Denis Kirjanov <[email-masked]>
Date: Mon, 11 May 2020 13:22:20 +0300

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.

Signed-off-by: Denis Kirjanov <[email-masked]>
---
 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;
-- 
1.8.3.1