// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2017 Covalent IO, Inc. http://covalent.io
 */

/* 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
 * a per-cpu flush list. The bpf_dtab_netdev object will not be destroyed  until
 * this list is empty, 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.
 *
 * The devmap_hash type is a map type which interprets keys as ifindexes and
 * indexes these using a hashmap. This allows maps that use ifindex as key to be
 * densely packed instead of having holes in the lookup array for unused
 * ifindexes. The setup and packet enqueue/send code is shared between the two
 * types of devmap; only the lookup and insertion is different.
 */
#include <linux/bpf.h>
#include <net/xdp.h>
#include <linux/filter.h>
#include <trace/events/xdp.h>

#define DEV_CREATE_FLAG_MASK \
        (BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY)

#define DEV_MAP_BULK_SIZE 16
struct bpf_dtab_netdev;

struct xdp_bulk_queue {
        struct xdp_frame *q[DEV_MAP_BULK_SIZE];
        struct list_head flush_node;
        struct net_device *dev_rx;
        struct bpf_dtab_netdev *obj;
        unsigned int count;
};

struct bpf_dtab_netdev {
        struct net_device *dev; /* must be first member, due to tracepoint */
        struct hlist_node index_hlist;
        struct bpf_dtab *dtab;
        struct xdp_bulk_queue __percpu *bulkq;
        struct rcu_head rcu;
        unsigned int idx; /* keep track of map index for tracepoint */
};

struct bpf_dtab {
        struct bpf_map map;
        struct bpf_dtab_netdev **netdev_map;
        struct list_head __percpu *flush_list;
        struct list_head list;

        /* these are only used for DEVMAP_HASH type maps */
        struct hlist_head *dev_index_head;
        spinlock_t index_lock;
        unsigned int items;
        u32 n_buckets;
};

static DEFINE_SPINLOCK(dev_map_lock);
static LIST_HEAD(dev_map_list);

static struct hlist_head *dev_map_create_hash(unsigned int entries)
{
        int i;
        struct hlist_head *hash;

        hash = kmalloc_array(entries, sizeof(*hash), GFP_KERNEL);
        if (hash != NULL)
                for (i = 0; i < entries; i++)
                        INIT_HLIST_HEAD(&hash[i]);

        return hash;
}

static int dev_map_init_map(struct bpf_dtab *dtab, union bpf_attr *attr)
{
        int err, cpu;
        u64 cost;

        /* check sanity of attributes */
        if (attr->max_entries == 0 || attr->key_size != 4 ||
            attr->value_size != 4 || attr->map_flags & ~DEV_CREATE_FLAG_MASK)
                return -EINVAL;

        /* Lookup returns a pointer straight to dev->ifindex, so make sure the
         * verifier prevents writes from the BPF side
         */
        attr->map_flags |= BPF_F_RDONLY_PROG;


        bpf_map_init_from_attr(&dtab->map, attr);

        /* make sure page count doesn't overflow */
        cost = (u64) dtab->map.max_entries * sizeof(struct bpf_dtab_netdev *);
        cost += sizeof(struct list_head) * num_possible_cpus();

        if (attr->map_type == BPF_MAP_TYPE_DEVMAP_HASH) {
                dtab->n_buckets = roundup_pow_of_two(dtab->map.max_entries);

                if (!dtab->n_buckets) /* Overflow check */
                        return -EINVAL;
                cost += (u64) sizeof(struct hlist_head) * dtab->n_buckets;
        }

        /* if map size is larger than memlock limit, reject it */
        err = bpf_map_charge_init(&dtab->map.memory, cost);
        if (err)
                return -EINVAL;

        dtab->flush_list = alloc_percpu(struct list_head);
        if (!dtab->flush_list)
                goto free_charge;

        for_each_possible_cpu(cpu)
                INIT_LIST_HEAD(per_cpu_ptr(dtab->flush_list, cpu));

        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_percpu;

        if (attr->map_type == BPF_MAP_TYPE_DEVMAP_HASH) {
                dtab->dev_index_head = dev_map_create_hash(dtab->n_buckets);
                if (!dtab->dev_index_head)
                        goto free_map_area;

                spin_lock_init(&dtab->index_lock);
        }

        return 0;

free_map_area:
        bpf_map_area_free(dtab->netdev_map);
free_percpu:
        free_percpu(dtab->flush_list);
free_charge:
        bpf_map_charge_finish(&dtab->map.memory);
        return -ENOMEM;
}

static struct bpf_map *dev_map_alloc(union bpf_attr *attr)
{
        struct bpf_dtab *dtab;
        int err;

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

        dtab = kzalloc(sizeof(*dtab), GFP_USER);
        if (!dtab)
                return ERR_PTR(-ENOMEM);

        err = dev_map_init_map(dtab, attr);
        if (err) {
                kfree(dtab);
                return ERR_PTR(err);
        }

        spin_lock(&dev_map_lock);
        list_add_tail_rcu(&dtab->list, &dev_map_list);
        spin_unlock(&dev_map_lock);

        return &dtab->map;
}

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);

        bpf_clear_redirect_map(map);
        synchronize_rcu();

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

        /* To ensure all pending flush operations have completed wait for flush
         * list to empty on _all_ cpus.
         * Because the above synchronize_rcu() ensures the map is disconnected
         * from the program we can assume no new items will be added.
         */
        for_each_online_cpu(cpu) {
                struct list_head *flush_list = per_cpu_ptr(dtab->flush_list, cpu);

                while (!list_empty(flush_list))
                        cond_resched();
        }

        for (i = 0; i < dtab->map.max_entries; i++) {
                struct bpf_dtab_netdev *dev;

                dev = dtab->netdev_map[i];
                if (!dev)
                        continue;

                free_percpu(dev->bulkq);
                dev_put(dev->dev);
                kfree(dev);
        }

        free_percpu(dtab->flush_list);
        bpf_map_area_free(dtab->netdev_map);
        kfree(dtab->dev_index_head);
        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;
}

static inline struct hlist_head *dev_map_index_hash(struct bpf_dtab *dtab,
                                                    int idx)
{
        return &dtab->dev_index_head[idx & (dtab->n_buckets - 1)];
}

struct bpf_dtab_netdev *__dev_map_hash_lookup_elem(struct bpf_map *map, u32 key)
{
        struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
        struct hlist_head *head = dev_map_index_hash(dtab, key);
        struct bpf_dtab_netdev *dev;

        hlist_for_each_entry_rcu(dev, head, index_hlist)
                if (dev->idx == key)
                        return dev;

        return NULL;
}

static int dev_map_hash_get_next_key(struct bpf_map *map, void *key,
                                    void *next_key)
{
        struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
        u32 idx, *next = next_key;
        struct bpf_dtab_netdev *dev, *next_dev;
        struct hlist_head *head;
        int i = 0;

        if (!key)
                goto find_first;

        idx = *(u32 *)key;

        dev = __dev_map_hash_lookup_elem(map, idx);
        if (!dev)
                goto find_first;

        next_dev = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(&dev->index_hlist)),
                                    struct bpf_dtab_netdev, index_hlist);

        if (next_dev) {
                *next = next_dev->idx;
                return 0;
        }

        i = idx & (dtab->n_buckets - 1);
        i++;

 find_first:
        for (; i < dtab->n_buckets; i++) {
                head = dev_map_index_hash(dtab, i);

                next_dev = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),
                                            struct bpf_dtab_netdev,
                                            index_hlist);
                if (next_dev) {
                        *next = next_dev->idx;
                        return 0;
                }
        }

        return -ENOENT;
}

static int bq_xmit_all(struct xdp_bulk_queue *bq, u32 flags,
                       bool in_napi_ctx)
{
        struct bpf_dtab_netdev *obj = bq->obj;
        struct net_device *dev = obj->dev;
        int sent = 0, drops = 0, err = 0;
        int i;

        if (unlikely(!bq->count))
                return 0;

        for (i = 0; i < bq->count; i++) {
                struct xdp_frame *xdpf = bq->q[i];

                prefetch(xdpf);
        }

        sent = dev->netdev_ops->ndo_xdp_xmit(dev, bq->count, bq->q, flags);
        if (sent < 0) {
                err = sent;
                sent = 0;
                goto error;
        }
        drops = bq->count - sent;
out:
        bq->count = 0;

        trace_xdp_devmap_xmit(&obj->dtab->map, obj->idx,
                              sent, drops, bq->dev_rx, dev, err);
        bq->dev_rx = NULL;
        __list_del_clearprev(&bq->flush_node);
        return 0;
error:
        /* If ndo_xdp_xmit fails with an errno, no frames have been
         * xmit'ed and it's our responsibility to them free all.
         */
        for (i = 0; i < bq->count; i++) {
                struct xdp_frame *xdpf = bq->q[i];

                /* RX path under NAPI protection, can return frames faster */
                if (likely(in_napi_ctx))
                        xdp_return_frame_rx_napi(xdpf);
                else
                        xdp_return_frame(xdpf);
                drops++;
        }
        goto out;
}

/* __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 flush list
 * is empty 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);
        struct list_head *flush_list = this_cpu_ptr(dtab->flush_list);
        struct xdp_bulk_queue *bq, *tmp;

        rcu_read_lock();
        list_for_each_entry_safe(bq, tmp, flush_list, flush_node)
                bq_xmit_all(bq, XDP_XMIT_FLUSH, true);
        rcu_read_unlock();
}

/* 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 bpf_dtab_netdev *__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 *obj;

        if (key >= map->max_entries)
                return NULL;

        obj = READ_ONCE(dtab->netdev_map[key]);
        return obj;
}

/* Runs under RCU-read-side, plus in softirq under NAPI protection.
 * Thus, safe percpu variable access.
 */
static int bq_enqueue(struct bpf_dtab_netdev *obj, struct xdp_frame *xdpf,
                      struct net_device *dev_rx)

{
        struct list_head *flush_list = this_cpu_ptr(obj->dtab->flush_list);
        struct xdp_bulk_queue *bq = this_cpu_ptr(obj->bulkq);

        if (unlikely(bq->count == DEV_MAP_BULK_SIZE))
                bq_xmit_all(bq, 0, true);

        /* Ingress dev_rx will be the same for all xdp_frame's in
         * bulk_queue, because bq stored per-CPU and must be flushed
         * from net_device drivers NAPI func end.
         */
        if (!bq->dev_rx)
                bq->dev_rx = dev_rx;

        bq->q[bq->count++] = xdpf;

        if (!bq->flush_node.prev)
                list_add(&bq->flush_node, flush_list);

        return 0;
}

int dev_map_enqueue(struct bpf_dtab_netdev *dst, struct xdp_buff *xdp,
                    struct net_device *dev_rx)
{
        struct net_device *dev = dst->dev;
        struct xdp_frame *xdpf;
        int err;

        if (!dev->netdev_ops->ndo_xdp_xmit)
                return -EOPNOTSUPP;

        err = xdp_ok_fwd_dev(dev, xdp->data_end - xdp->data);
        if (unlikely(err))
                return err;

        xdpf = convert_to_xdp_frame(xdp);
        if (unlikely(!xdpf))
                return -EOVERFLOW;

        return bq_enqueue(dst, xdpf, dev_rx);
}

int dev_map_generic_redirect(struct bpf_dtab_netdev *dst, struct sk_buff *skb,
                             struct bpf_prog *xdp_prog)
{
        int err;

        err = xdp_ok_fwd_dev(dst->dev, skb->len);
        if (unlikely(err))
                return err;
        skb->dev = dst->dev;
        generic_xdp_tx(skb, xdp_prog);

        return 0;
}

static void *dev_map_lookup_elem(struct bpf_map *map, void *key)
{
        struct bpf_dtab_netdev *obj = __dev_map_lookup_elem(map, *(u32 *)key);
        struct net_device *dev = obj ? obj->dev : NULL;

        return dev ? &dev->ifindex : NULL;
}

static void *dev_map_hash_lookup_elem(struct bpf_map *map, void *key)
{
        struct bpf_dtab_netdev *obj = __dev_map_hash_lookup_elem(map,
                                                                *(u32 *)key);
        struct net_device *dev = obj ? obj->dev : NULL;

        return dev ? &dev->ifindex : NULL;
}

static void dev_map_flush_old(struct bpf_dtab_netdev *dev)
{
        if (dev->dev->netdev_ops->ndo_xdp_xmit) {
                struct xdp_bulk_queue *bq;
                int cpu;

                rcu_read_lock();
                for_each_online_cpu(cpu) {
                        bq = per_cpu_ptr(dev->bulkq, cpu);
                        bq_xmit_all(bq, XDP_XMIT_FLUSH, false);
                }
                rcu_read_unlock();
        }
}

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);
        free_percpu(dev->bulkq);
        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_hash_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;
        unsigned long flags;
        int ret = -ENOENT;

        spin_lock_irqsave(&dtab->index_lock, flags);

        old_dev = __dev_map_hash_lookup_elem(map, k);
        if (old_dev) {
                dtab->items--;
                hlist_del_init_rcu(&old_dev->index_hlist);
                call_rcu(&old_dev->rcu, __dev_map_entry_free);
                ret = 0;
        }
        spin_unlock_irqrestore(&dtab->index_lock, flags);

        return ret;
}

static struct bpf_dtab_netdev *__dev_map_alloc_node(struct net *net,
                                                    struct bpf_dtab *dtab,
                                                    u32 ifindex,
                                                    unsigned int idx)
{
        gfp_t gfp = GFP_ATOMIC | __GFP_NOWARN;
        struct bpf_dtab_netdev *dev;
        struct xdp_bulk_queue *bq;
        int cpu;

        dev = kmalloc_node(sizeof(*dev), gfp, dtab->map.numa_node);
        if (!dev)
                return ERR_PTR(-ENOMEM);

        dev->bulkq = __alloc_percpu_gfp(sizeof(*dev->bulkq),
                                        sizeof(void *), gfp);
        if (!dev->bulkq) {
                kfree(dev);
                return ERR_PTR(-ENOMEM);
        }

        for_each_possible_cpu(cpu) {
                bq = per_cpu_ptr(dev->bulkq, cpu);
                bq->obj = dev;
        }

        dev->dev = dev_get_by_index(net, ifindex);
        if (!dev->dev) {
                free_percpu(dev->bulkq);
                kfree(dev);
                return ERR_PTR(-EINVAL);
        }

        dev->idx = idx;
        dev->dtab = dtab;

        return dev;
}

static int __dev_map_update_elem(struct net *net, struct bpf_map *map,
                                 void *key, void *value, u64 map_flags)
{
        struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
        struct bpf_dtab_netdev *dev, *old_dev;
        u32 ifindex = *(u32 *)value;
        u32 i = *(u32 *)key;

        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 = __dev_map_alloc_node(net, dtab, ifindex, i);
                if (IS_ERR(dev))
                        return PTR_ERR(dev);
        }

        /* 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;
}

static int dev_map_update_elem(struct bpf_map *map, void *key, void *value,
                               u64 map_flags)
{
        return __dev_map_update_elem(current->nsproxy->net_ns,
                                     map, key, value, map_flags);
}

static int __dev_map_hash_update_elem(struct net *net, struct bpf_map *map,
                                     void *key, void *value, u64 map_flags)
{
        struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
        struct bpf_dtab_netdev *dev, *old_dev;
        u32 ifindex = *(u32 *)value;
        u32 idx = *(u32 *)key;
        unsigned long flags;
        int err = -EEXIST;

        if (unlikely(map_flags > BPF_EXIST || !ifindex))
                return -EINVAL;

        spin_lock_irqsave(&dtab->index_lock, flags);

        old_dev = __dev_map_hash_lookup_elem(map, idx);
        if (old_dev && (map_flags & BPF_NOEXIST))
                goto out_err;

        dev = __dev_map_alloc_node(net, dtab, ifindex, idx);
        if (IS_ERR(dev)) {
                err = PTR_ERR(dev);
                goto out_err;
        }

        if (old_dev) {
                hlist_del_rcu(&old_dev->index_hlist);
        } else {
                if (dtab->items >= dtab->map.max_entries) {
                        spin_unlock_irqrestore(&dtab->index_lock, flags);
                        call_rcu(&dev->rcu, __dev_map_entry_free);
                        return -E2BIG;
                }
                dtab->items++;
        }

        hlist_add_head_rcu(&dev->index_hlist,
                           dev_map_index_hash(dtab, idx));
        spin_unlock_irqrestore(&dtab->index_lock, flags);

        if (old_dev)
                call_rcu(&old_dev->rcu, __dev_map_entry_free);

        return 0;

out_err:
        spin_unlock_irqrestore(&dtab->index_lock, flags);
        return err;
}

static int dev_map_hash_update_elem(struct bpf_map *map, void *key, void *value,
                                   u64 map_flags)
{
        return __dev_map_hash_update_elem(current->nsproxy->net_ns,
                                         map, key, value, map_flags);
}

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,
        .map_check_btf = map_check_no_btf,
};

const struct bpf_map_ops dev_map_hash_ops = {
        .map_alloc = dev_map_alloc,
        .map_free = dev_map_free,
        .map_get_next_key = dev_map_hash_get_next_key,
        .map_lookup_elem = dev_map_hash_lookup_elem,
        .map_update_elem = dev_map_hash_update_elem,
        .map_delete_elem = dev_map_hash_delete_elem,
        .map_check_btf = map_check_no_btf,
};

static void dev_map_hash_remove_netdev(struct bpf_dtab *dtab,
                                       struct net_device *netdev)
{
        unsigned long flags;
        u32 i;

        spin_lock_irqsave(&dtab->index_lock, flags);
        for (i = 0; i < dtab->n_buckets; i++) {
                struct bpf_dtab_netdev *dev;
                struct hlist_head *head;
                struct hlist_node *next;

                head = dev_map_index_hash(dtab, i);

                hlist_for_each_entry_safe(dev, next, head, index_hlist) {
                        if (netdev != dev->dev)
                                continue;

                        dtab->items--;
                        hlist_del_rcu(&dev->index_hlist);
                        call_rcu(&dev->rcu, __dev_map_entry_free);
                }
        }
        spin_unlock_irqrestore(&dtab->index_lock, flags);
}

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) {
                        if (dtab->map.map_type == BPF_MAP_TYPE_DEVMAP_HASH) {
                                dev_map_hash_remove_netdev(dtab, netdev);
                                continue;
                        }

                        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)
{
        /* Assure tracepoint shadow struct _bpf_dtab_netdev is in sync */
        BUILD_BUG_ON(offsetof(struct bpf_dtab_netdev, dev) !=
                     offsetof(struct _bpf_dtab_netdev, dev));
        register_netdevice_notifier(&dev_map_notifier);
        return 0;
}

subsys_initcall(dev_map_init);