[PATCH net-next v2] xen-netfront: add basic XDP support

[Denis Kirjanov <kda@linux-powerpc.org>]

the patch adds a basic xdo logic to the netfront driver

XDP redirect is not supported yet

v2:
- avoid data copying while passing to XDP
- tell xen-natback that we need the headroom space

Signed-off-by: Denis Kirjanov <kda@linux-powerpc.org>
---
 drivers/net/xen-netback/common.h |   1 +
 drivers/net/xen-netback/rx.c     |   9 ++-
 drivers/net/xen-netback/xenbus.c |  21 ++++++
 drivers/net/xen-netfront.c       | 157 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 186 insertions(+), 2 deletions(-)

diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h
index 05847eb..0750c6f 100644
--- a/drivers/net/xen-netback/common.h
+++ b/drivers/net/xen-netback/common.h
@@ -280,6 +280,7 @@ struct xenvif {
 	u8 ip_csum:1;
 	u8 ipv6_csum:1;
 	u8 multicast_control:1;
+	u8 xdp_enabled:1;
 
 	/* Is this interface disabled? True when backend discovers
 	 * frontend is rogue.
diff --git a/drivers/net/xen-netback/rx.c b/drivers/net/xen-netback/rx.c
index ef58870..a110a59 100644
--- a/drivers/net/xen-netback/rx.c
+++ b/drivers/net/xen-netback/rx.c
@@ -33,6 +33,11 @@
 #include <xen/xen.h>
 #include <xen/events.h>
 
+static inline int xenvif_rx_xdp_offset(struct xenvif *vif)
+{
+	return (vif->xdp_enabled ? XDP_PACKET_HEADROOM : 0);
+}
+
 static bool xenvif_rx_ring_slots_available(struct xenvif_queue *queue)
 {
 	RING_IDX prod, cons;
@@ -356,7 +361,7 @@ static void xenvif_rx_data_slot(struct xenvif_queue *queue,
 				struct xen_netif_rx_request *req,
 				struct xen_netif_rx_response *rsp)
 {
-	unsigned int offset = 0;
+	unsigned int offset = xenvif_rx_xdp_offset(queue->vif);
 	unsigned int flags;
 
 	do {
@@ -389,7 +394,7 @@ static void xenvif_rx_data_slot(struct xenvif_queue *queue,
 			flags |= XEN_NETRXF_extra_info;
 	}
 
-	rsp->offset = 0;
+	rsp->offset = xenvif_rx_xdp_offset(queue->vif);
 	rsp->flags = flags;
 	rsp->id = req->id;
 	rsp->status = (s16)offset;
diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
index 286054b..81a6023 100644
--- a/drivers/net/xen-netback/xenbus.c
+++ b/drivers/net/xen-netback/xenbus.c
@@ -393,6 +393,20 @@ static void set_backend_state(struct backend_info *be,
 	}
 }
 
+static void read_xenbus_fronetend_xdp(struct backend_info *be,
+				      struct xenbus_device *dev)
+{
+	struct xenvif *vif = be->vif;
+	unsigned int val;
+	int err;
+
+	err = xenbus_scanf(XBT_NIL, dev->otherend,
+			   "feature-xdp", "%u", &val);
+	if (err < 0)
+		return;
+	vif->xdp_enabled = val;
+}
+
 /**
  * Callback received when the frontend's state changes.
  */
@@ -417,6 +431,11 @@ static void frontend_changed(struct xenbus_device *dev,
 		set_backend_state(be, XenbusStateConnected);
 		break;
 
+	case XenbusStateReconfiguring:
+		read_xenbus_fronetend_xdp(be, dev);
+		xenbus_switch_state(dev, XenbusStateReconfigured);
+		break;
+
 	case XenbusStateClosing:
 		set_backend_state(be, XenbusStateClosing);
 		break;
@@ -935,6 +954,8 @@ static int read_xenbus_vif_flags(struct backend_info *be)
 
 	vif->gso_mask = 0;
 
+	vif->xdp_enabled = 0;
+
 	if (xenbus_read_unsigned(dev->otherend, "feature-gso-tcpv4", 0))
 		vif->gso_mask |= GSO_BIT(TCPV4);
 
diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 482c6c8..db8a280 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -44,6 +44,8 @@
 #include <linux/mm.h>
 #include <linux/slab.h>
 #include <net/ip.h>
+#include <linux/bpf.h>
+#include <linux/bpf_trace.h>
 
 #include <xen/xen.h>
 #include <xen/xenbus.h>
@@ -102,6 +104,8 @@ 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
@@ -778,6 +782,40 @@ static int xennet_get_extras(struct netfront_queue *queue,
 	return err;
 }
 
+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:
+		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