1 files changed, 409 insertions, 0 deletions
diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
new file mode 100644
index 0000000..ecf9f99
--- /dev/null
+++ b/kernel/bpf/devmap.c
@@ -0,0 +1,409 @@
+/* Copyright (c) 2017 Covalent IO, Inc. http://covalent.io
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ */
+
+/* Devmaps primary use is as a backend map for XDP BPF helper call
+ * bpf_redirect_map(). Because XDP is mostly concerned with performance we
+ * spent some effort to ensure the datapath with redirect maps does not use
+ * any locking. This is a quick note on the details.
+ *
+ * We have three possible paths to get into the devmap control plane bpf
+ * syscalls, bpf programs, and driver side xmit/flush operations. A bpf syscall
+ * will invoke an update, delete, or lookup operation. To ensure updates and
+ * deletes appear atomic from the datapath side xchg() is used to modify the
+ * netdev_map array. Then because the datapath does a lookup into the netdev_map
+ * array (read-only) from an RCU critical section we use call_rcu() to wait for
+ * an rcu grace period before free'ing the old data structures. This ensures the
+ * datapath always has a valid copy. However, the datapath does a "flush"
+ * operation that pushes any pending packets in the driver outside the RCU
+ * critical section. Each bpf_dtab_netdev tracks these pending operations using
+ * an atomic per-cpu bitmap. The bpf_dtab_netdev object will not be destroyed
+ * until all bits are cleared indicating outstanding flush operations have
+ * completed.
+ *
+ * BPF syscalls may race with BPF program calls on any of the update, delete
+ * or lookup operations. As noted above the xchg() operation also keep the
+ * netdev_map consistent in this case. From the devmap side BPF programs
+ * calling into these operations are the same as multiple user space threads
+ * making system calls.
+ *
+ * Finally, any of the above may race with a netdev_unregister notifier. The
+ * unregister notifier must search for net devices in the map structure that
+ * contain a reference to the net device and remove them. This is a two step
+ * process (a) dereference the bpf_dtab_netdev object in netdev_map and (b)
+ * check to see if the ifindex is the same as the net_device being removed.
+ * When removing the dev a cmpxchg() is used to ensure the correct dev is
+ * removed, in the case of a concurrent update or delete operation it is
+ * possible that the initially referenced dev is no longer in the map. As the
+ * notifier hook walks the map we know that new dev references can not be
+ * added by the user because core infrastructure ensures dev_get_by_index()
+ * calls will fail at this point.
+ */
+#include <linux/bpf.h>
+#include <linux/filter.h>
+
+struct bpf_dtab_netdev {
+	struct net_device *dev;
+	struct bpf_dtab *dtab;
+	unsigned int bit;
+	struct rcu_head rcu;
+};
+
+struct bpf_dtab {
+	struct bpf_map map;
+	struct bpf_dtab_netdev **netdev_map;
+	unsigned long __percpu *flush_needed;
+	struct list_head list;
+};
+
+static DEFINE_SPINLOCK(dev_map_lock);
+static LIST_HEAD(dev_map_list);
+
+static u64 dev_map_bitmap_size(const union bpf_attr *attr)
+{
+	return BITS_TO_LONGS(attr->max_entries) * sizeof(unsigned long);
+}
+
+static struct bpf_map *dev_map_alloc(union bpf_attr *attr)
+{
+	struct bpf_dtab *dtab;
+	u64 cost;
+	int err;
+
+	/* check sanity of attributes */
+	if (attr->max_entries == 0 || attr->key_size != 4 ||
+	    attr->value_size != 4 || attr->map_flags & ~BPF_F_NUMA_NODE)
+		return ERR_PTR(-EINVAL);
+
+	dtab = kzalloc(sizeof(*dtab), GFP_USER);
+	if (!dtab)
+		return ERR_PTR(-ENOMEM);
+
+	/* mandatory map attributes */
+	dtab->map.map_type = attr->map_type;
+	dtab->map.key_size = attr->key_size;
+	dtab->map.value_size = attr->value_size;
+	dtab->map.max_entries = attr->max_entries;
+	dtab->map.map_flags = attr->map_flags;
+	dtab->map.numa_node = bpf_map_attr_numa_node(attr);
+
+	/* make sure page count doesn't overflow */
+	cost = (u64) dtab->map.max_entries * sizeof(struct bpf_dtab_netdev *);
+	cost += dev_map_bitmap_size(attr) * num_possible_cpus();
+	if (cost >= U32_MAX - PAGE_SIZE)
+		goto free_dtab;
+
+	dtab->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;
+
+	/* if map size is larger than memlock limit, reject it early */
+	err = bpf_map_precharge_memlock(dtab->map.pages);
+	if (err)
+		goto free_dtab;
+
+	/* A per cpu bitfield with a bit per possible net device */
+	dtab->flush_needed = __alloc_percpu(dev_map_bitmap_size(attr),
+					    __alignof__(unsigned long));
+	if (!dtab->flush_needed)
+		goto free_dtab;
+
+	dtab->netdev_map = bpf_map_area_alloc(dtab->map.max_entries *
+					      sizeof(struct bpf_dtab_netdev *),
+					      dtab->map.numa_node);
+	if (!dtab->netdev_map)
+		goto free_dtab;
+
+	spin_lock(&dev_map_lock);
+	list_add_tail_rcu(&dtab->list, &dev_map_list);
+	spin_unlock(&dev_map_lock);
+
+	return &dtab->map;
+free_dtab:
+	free_percpu(dtab->flush_needed);
+	kfree(dtab);
+	return ERR_PTR(-ENOMEM);
+}
+
+static void dev_map_free(struct bpf_map *map)
+{
+	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
+	int i, cpu;
+
+	/* At this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
+	 * so the programs (can be more than one that used this map) were
+	 * disconnected from events. Wait for outstanding critical sections in
+	 * these programs to complete. The rcu critical section only guarantees
+	 * no further reads against netdev_map. It does __not__ ensure pending
+	 * flush operations (if any) are complete.
+	 */
+
+	spin_lock(&dev_map_lock);
+	list_del_rcu(&dtab->list);
+	spin_unlock(&dev_map_lock);
+
+	synchronize_rcu();
+
+	/* To ensure all pending flush operations have completed wait for flush
+	 * bitmap to indicate all flush_needed bits to be zero on _all_ cpus.
+	 * Because the above synchronize_rcu() ensures the map is disconnected
+	 * from the program we can assume no new bits will be set.
+	 */
+	for_each_online_cpu(cpu) {
+		unsigned long *bitmap = per_cpu_ptr(dtab->flush_needed, cpu);
+
+		while (!bitmap_empty(bitmap, dtab->map.max_entries))
+			cpu_relax();
+	}
+
+	for (i = 0; i < dtab->map.max_entries; i++) {
+		struct bpf_dtab_netdev *dev;
+
+		dev = dtab->netdev_map[i];
+		if (!dev)
+			continue;
+
+		dev_put(dev->dev);
+		kfree(dev);
+	}
+
+	free_percpu(dtab->flush_needed);
+	bpf_map_area_free(dtab->netdev_map);
+	kfree(dtab);
+}
+
+static int dev_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
+{
+	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
+	u32 index = key ? *(u32 *)key : U32_MAX;
+	u32 *next = next_key;
+
+	if (index >= dtab->map.max_entries) {
+		*next = 0;
+		return 0;
+	}
+
+	if (index == dtab->map.max_entries - 1)
+		return -ENOENT;
+	*next = index + 1;
+	return 0;
+}
+
+void __dev_map_insert_ctx(struct bpf_map *map, u32 bit)
+{
+	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
+	unsigned long *bitmap = this_cpu_ptr(dtab->flush_needed);
+
+	__set_bit(bit, bitmap);
+}
+
+/* __dev_map_flush is called from xdp_do_flush_map() which _must_ be signaled
+ * from the driver before returning from its napi->poll() routine. The poll()
+ * routine is called either from busy_poll context or net_rx_action signaled
+ * from NET_RX_SOFTIRQ. Either way the poll routine must complete before the
+ * net device can be torn down. On devmap tear down we ensure the ctx bitmap
+ * is zeroed before completing to ensure all flush operations have completed.
+ */
+void __dev_map_flush(struct bpf_map *map)
+{
+	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
+	unsigned long *bitmap = this_cpu_ptr(dtab->flush_needed);
+	u32 bit;
+
+	for_each_set_bit(bit, bitmap, map->max_entries) {
+		struct bpf_dtab_netdev *dev = READ_ONCE(dtab->netdev_map[bit]);
+		struct net_device *netdev;
+
+		/* This is possible if the dev entry is removed by user space
+		 * between xdp redirect and flush op.
+		 */
+		if (unlikely(!dev))
+			continue;
+
+		__clear_bit(bit, bitmap);
+		netdev = dev->dev;
+		if (likely(netdev->netdev_ops->ndo_xdp_flush))
+			netdev->netdev_ops->ndo_xdp_flush(netdev);
+	}
+}
+
+/* rcu_read_lock (from syscall and BPF contexts) ensures that if a delete and/or
+ * update happens in parallel here a dev_put wont happen until after reading the
+ * ifindex.
+ */
+struct net_device  *__dev_map_lookup_elem(struct bpf_map *map, u32 key)
+{
+	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
+	struct bpf_dtab_netdev *dev;
+
+	if (key >= map->max_entries)
+		return NULL;
+
+	dev = READ_ONCE(dtab->netdev_map[key]);
+	return dev ? dev->dev : NULL;
+}
+
+static void *dev_map_lookup_elem(struct bpf_map *map, void *key)
+{
+	struct net_device *dev = __dev_map_lookup_elem(map, *(u32 *)key);
+
+	return dev ? &dev->ifindex : NULL;
+}
+
+static void dev_map_flush_old(struct bpf_dtab_netdev *dev)
+{
+	if (dev->dev->netdev_ops->ndo_xdp_flush) {
+		struct net_device *fl = dev->dev;
+		unsigned long *bitmap;
+		int cpu;
+
+		for_each_online_cpu(cpu) {
+			bitmap = per_cpu_ptr(dev->dtab->flush_needed, cpu);
+			__clear_bit(dev->bit, bitmap);
+
+			fl->netdev_ops->ndo_xdp_flush(dev->dev);
+		}
+	}
+}
+
+static void __dev_map_entry_free(struct rcu_head *rcu)
+{
+	struct bpf_dtab_netdev *dev;
+
+	dev = container_of(rcu, struct bpf_dtab_netdev, rcu);
+	dev_map_flush_old(dev);
+	dev_put(dev->dev);
+	kfree(dev);
+}
+
+static int dev_map_delete_elem(struct bpf_map *map, void *key)
+{
+	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
+	struct bpf_dtab_netdev *old_dev;
+	int k = *(u32 *)key;
+
+	if (k >= map->max_entries)
+		return -EINVAL;
+
+	/* Use call_rcu() here to ensure any rcu critical sections have
+	 * completed, but this does not guarantee a flush has happened
+	 * yet. Because driver side rcu_read_lock/unlock only protects the
+	 * running XDP program. However, for pending flush operations the
+	 * dev and ctx are stored in another per cpu map. And additionally,
+	 * the driver tear down ensures all soft irqs are complete before
+	 * removing the net device in the case of dev_put equals zero.
+	 */
+	old_dev = xchg(&dtab->netdev_map[k], NULL);
+	if (old_dev)
+		call_rcu(&old_dev->rcu, __dev_map_entry_free);
+	return 0;
+}
+
+static int dev_map_update_elem(struct bpf_map *map, void *key, void *value,
+				u64 map_flags)
+{
+	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
+	struct net *net = current->nsproxy->net_ns;
+	struct bpf_dtab_netdev *dev, *old_dev;
+	u32 i = *(u32 *)key;
+	u32 ifindex = *(u32 *)value;
+
+	if (unlikely(map_flags > BPF_EXIST))
+		return -EINVAL;
+	if (unlikely(i >= dtab->map.max_entries))
+		return -E2BIG;
+	if (unlikely(map_flags == BPF_NOEXIST))
+		return -EEXIST;
+
+	if (!ifindex) {
+		dev = NULL;
+	} else {
+		dev = kmalloc_node(sizeof(*dev), GFP_ATOMIC | __GFP_NOWARN,
+				   map->numa_node);
+		if (!dev)
+			return -ENOMEM;
+
+		dev->dev = dev_get_by_index(net, ifindex);
+		if (!dev->dev) {
+			kfree(dev);
+			return -EINVAL;
+		}
+
+		dev->bit = i;
+		dev->dtab = dtab;
+	}
+
+	/* Use call_rcu() here to ensure rcu critical sections have completed
+	 * Remembering the driver side flush operation will happen before the
+	 * net device is removed.
+	 */
+	old_dev = xchg(&dtab->netdev_map[i], dev);
+	if (old_dev)
+		call_rcu(&old_dev->rcu, __dev_map_entry_free);
+
+	return 0;
+}
+
+const struct bpf_map_ops dev_map_ops = {
+	.map_alloc = dev_map_alloc,
+	.map_free = dev_map_free,
+	.map_get_next_key = dev_map_get_next_key,
+	.map_lookup_elem = dev_map_lookup_elem,
+	.map_update_elem = dev_map_update_elem,
+	.map_delete_elem = dev_map_delete_elem,
+};
+
+static int dev_map_notification(struct notifier_block *notifier,
+				ulong event, void *ptr)
+{
+	struct net_device *netdev = netdev_notifier_info_to_dev(ptr);
+	struct bpf_dtab *dtab;
+	int i;
+
+	switch (event) {
+	case NETDEV_UNREGISTER:
+		/* This rcu_read_lock/unlock pair is needed because
+		 * dev_map_list is an RCU list AND to ensure a delete
+		 * operation does not free a netdev_map entry while we
+		 * are comparing it against the netdev being unregistered.
+		 */
+		rcu_read_lock();
+		list_for_each_entry_rcu(dtab, &dev_map_list, list) {
+			for (i = 0; i < dtab->map.max_entries; i++) {
+				struct bpf_dtab_netdev *dev, *odev;
+
+				dev = READ_ONCE(dtab->netdev_map[i]);
+				if (!dev ||
+				    dev->dev->ifindex != netdev->ifindex)
+					continue;
+				odev = cmpxchg(&dtab->netdev_map[i], dev, NULL);
+				if (dev == odev)
+					call_rcu(&dev->rcu,
+						 __dev_map_entry_free);
+			}
+		}
+		rcu_read_unlock();
+		break;
+	default:
+		break;
+	}
+	return NOTIFY_OK;
+}
+
+static struct notifier_block dev_map_notifier = {
+	.notifier_call = dev_map_notification,
+};
+
+static int __init dev_map_init(void)
+{
+	register_netdevice_notifier(&dev_map_notifier);
+	return 0;
+}
+
+subsys_initcall(dev_map_init);