kernel/bpf/devmap.c - LeafOS-Devices/android_kernel_samsung_gta4xl - Gitiles

 /* 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((u64) attr->max_entries) * sizeof(unsigned long);
 }

 static struct bpf_map *dev_map_alloc(union bpf_attr *attr)
 {
 	struct bpf_dtab *dtab;
 	int err = -EINVAL;
 	u64 cost;

 	if (!capable(CAP_NET_ADMIN))
 		return ERR_PTR(-EPERM);

 	/* 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;

 	err = -ENOMEM;

 	/* A per cpu bitfield with a bit per possible net device */
 	dtab->flush_needed = __alloc_percpu_gfp(dev_map_bitmap_size(attr),
 						__alignof__(unsigned long),
 						GFP_KERNEL | __GFP_NOWARN);
 	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(err);
 }

 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();

 	/* Make sure prior __dev_map_entry_free() have completed. */
 	rcu_barrier();

 	/* 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))
 			cond_resched();
 	}

 	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 || netdev != dev->dev)
 					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);
	/* 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((u64) attr->max_entries) * sizeof(unsigned long);
	}

	static struct bpf_map dev_map_alloc(union bpf_attr attr)
	{
	struct bpf_dtab *dtab;
	int err = -EINVAL;
	u64 cost;

	if (!capable(CAP_NET_ADMIN))
	return ERR_PTR(-EPERM);

	/* 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;

	err = -ENOMEM;

	/* A per cpu bitfield with a bit per possible net device */
	dtab->flush_needed = __alloc_percpu_gfp(dev_map_bitmap_size(attr),
	__alignof__(unsigned long),
	GFP_KERNEL \| __GFP_NOWARN);
	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(err);
	}

	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();

	/* Make sure prior __dev_map_entry_free() have completed. */
	rcu_barrier();

	/* 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))
	cond_resched();
	}

	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 \|\| netdev != dev->dev)
	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);