--- /dev/null
+/* 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.
+ */
+#include <linux/bpf.h>
+#include <linux/jhash.h>
+#include <linux/filter.h>
+#include <linux/rculist_nulls.h>
+#include "percpu_freelist.h"
+#include "bpf_lru_list.h"
+#include "map_in_map.h"
+
+struct bpf_dtab_netdev {
+ struct net_device *dev;
+ int key;
+ struct rcu_head rcu;
+ struct bpf_dtab *dtab;
+};
+
+struct bpf_dtab {
+ struct bpf_map map;
+ struct bpf_dtab_netdev **netdev_map;
+};
+
+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)
+ return ERR_PTR(-EINVAL);
+
+ /* if value_size is bigger, the user space won't be able to
+ * access the elements.
+ */
+ if (attr->value_size > KMALLOC_MAX_SIZE)
+ return ERR_PTR(-E2BIG);
+
+ 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;
+
+ err = -ENOMEM;
+
+ /* make sure page count doesn't overflow */
+ cost = (u64) dtab->map.max_entries * sizeof(struct bpf_dtab_netdev *);
+ 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;
+
+ dtab->netdev_map = bpf_map_area_alloc(dtab->map.max_entries *
+ sizeof(struct bpf_dtab_netdev *));
+ if (!dtab->netdev_map)
+ goto free_dtab;
+
+ return &dtab->map;
+
+free_dtab:
+ 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;
+
+ /* 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.
+ */
+ synchronize_rcu();
+
+ 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);
+ }
+
+ /* At this point bpf program is detached and all pending operations
+ * _must_ be complete
+ */
+ 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 = (u32 *)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;
+}
+
+/* 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.
+ */
+static void *dev_map_lookup_elem(struct bpf_map *map, void *key)
+{
+ struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
+ struct bpf_dtab_netdev *dev;
+ u32 i = *(u32 *)key;
+
+ if (i >= map->max_entries)
+ return NULL;
+
+ dev = READ_ONCE(dtab->netdev_map[i]);
+ return dev ? &dev->dev->ifindex : NULL;
+}
+
+static void __dev_map_entry_free(struct rcu_head *rcu)
+{
+ struct bpf_dtab_netdev *old_dev;
+
+ old_dev = container_of(rcu, struct bpf_dtab_netdev, rcu);
+ dev_put(old_dev->dev);
+ kfree(old_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 synchronize_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(sizeof(*dev), GFP_ATOMIC | __GFP_NOWARN);
+ if (!dev)
+ return -ENOMEM;
+
+ dev->dev = dev_get_by_index(net, ifindex);
+ if (!dev->dev) {
+ kfree(dev);
+ return -EINVAL;
+ }
+
+ dev->key = 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,
+};
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