1 /* Copyright (c) 2017 Covalent IO, Inc. http://covalent.io
3 * This program is free software; you can redistribute it and/or
4 * modify it under the terms of version 2 of the GNU General Public
5 * License as published by the Free Software Foundation.
7 * This program is distributed in the hope that it will be useful, but
8 * WITHOUT ANY WARRANTY; without even the implied warranty of
9 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
10 * General Public License for more details.
13 /* Devmaps primary use is as a backend map for XDP BPF helper call
14 * bpf_redirect_map(). Because XDP is mostly concerned with performance we
15 * spent some effort to ensure the datapath with redirect maps does not use
16 * any locking. This is a quick note on the details.
18 * We have three possible paths to get into the devmap control plane bpf
19 * syscalls, bpf programs, and driver side xmit/flush operations. A bpf syscall
20 * will invoke an update, delete, or lookup operation. To ensure updates and
21 * deletes appear atomic from the datapath side xchg() is used to modify the
22 * netdev_map array. Then because the datapath does a lookup into the netdev_map
23 * array (read-only) from an RCU critical section we use call_rcu() to wait for
24 * an rcu grace period before free'ing the old data structures. This ensures the
25 * datapath always has a valid copy. However, the datapath does a "flush"
26 * operation that pushes any pending packets in the driver outside the RCU
27 * critical section. Each bpf_dtab_netdev tracks these pending operations using
28 * an atomic per-cpu bitmap. The bpf_dtab_netdev object will not be destroyed
29 * until all bits are cleared indicating outstanding flush operations have
32 * BPF syscalls may race with BPF program calls on any of the update, delete
33 * or lookup operations. As noted above the xchg() operation also keep the
34 * netdev_map consistent in this case. From the devmap side BPF programs
35 * calling into these operations are the same as multiple user space threads
36 * making system calls.
38 * Finally, any of the above may race with a netdev_unregister notifier. The
39 * unregister notifier must search for net devices in the map structure that
40 * contain a reference to the net device and remove them. This is a two step
41 * process (a) dereference the bpf_dtab_netdev object in netdev_map and (b)
42 * check to see if the ifindex is the same as the net_device being removed.
43 * When removing the dev a cmpxchg() is used to ensure the correct dev is
44 * removed, in the case of a concurrent update or delete operation it is
45 * possible that the initially referenced dev is no longer in the map. As the
46 * notifier hook walks the map we know that new dev references can not be
47 * added by the user because core infrastructure ensures dev_get_by_index()
48 * calls will fail at this point.
50 #include <linux/bpf.h>
51 #include <linux/filter.h>
53 struct bpf_dtab_netdev
{
54 struct net_device
*dev
;
55 struct bpf_dtab
*dtab
;
62 struct bpf_dtab_netdev
**netdev_map
;
63 unsigned long __percpu
*flush_needed
;
64 struct list_head list
;
67 static DEFINE_SPINLOCK(dev_map_lock
);
68 static LIST_HEAD(dev_map_list
);
70 static u64
dev_map_bitmap_size(const union bpf_attr
*attr
)
72 return BITS_TO_LONGS(attr
->max_entries
) * sizeof(unsigned long);
75 static struct bpf_map
*dev_map_alloc(union bpf_attr
*attr
)
77 struct bpf_dtab
*dtab
;
81 /* check sanity of attributes */
82 if (attr
->max_entries
== 0 || attr
->key_size
!= 4 ||
83 attr
->value_size
!= 4 || attr
->map_flags
& ~BPF_F_NUMA_NODE
)
84 return ERR_PTR(-EINVAL
);
86 dtab
= kzalloc(sizeof(*dtab
), GFP_USER
);
88 return ERR_PTR(-ENOMEM
);
90 /* mandatory map attributes */
91 dtab
->map
.map_type
= attr
->map_type
;
92 dtab
->map
.key_size
= attr
->key_size
;
93 dtab
->map
.value_size
= attr
->value_size
;
94 dtab
->map
.max_entries
= attr
->max_entries
;
95 dtab
->map
.map_flags
= attr
->map_flags
;
96 dtab
->map
.numa_node
= bpf_map_attr_numa_node(attr
);
98 /* make sure page count doesn't overflow */
99 cost
= (u64
) dtab
->map
.max_entries
* sizeof(struct bpf_dtab_netdev
*);
100 cost
+= dev_map_bitmap_size(attr
) * num_possible_cpus();
101 if (cost
>= U32_MAX
- PAGE_SIZE
)
104 dtab
->map
.pages
= round_up(cost
, PAGE_SIZE
) >> PAGE_SHIFT
;
106 /* if map size is larger than memlock limit, reject it early */
107 err
= bpf_map_precharge_memlock(dtab
->map
.pages
);
111 /* A per cpu bitfield with a bit per possible net device */
112 dtab
->flush_needed
= __alloc_percpu(dev_map_bitmap_size(attr
),
113 __alignof__(unsigned long));
114 if (!dtab
->flush_needed
)
117 dtab
->netdev_map
= bpf_map_area_alloc(dtab
->map
.max_entries
*
118 sizeof(struct bpf_dtab_netdev
*),
119 dtab
->map
.numa_node
);
120 if (!dtab
->netdev_map
)
123 spin_lock(&dev_map_lock
);
124 list_add_tail_rcu(&dtab
->list
, &dev_map_list
);
125 spin_unlock(&dev_map_lock
);
129 free_percpu(dtab
->flush_needed
);
131 return ERR_PTR(-ENOMEM
);
134 static void dev_map_free(struct bpf_map
*map
)
136 struct bpf_dtab
*dtab
= container_of(map
, struct bpf_dtab
, map
);
139 /* At this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
140 * so the programs (can be more than one that used this map) were
141 * disconnected from events. Wait for outstanding critical sections in
142 * these programs to complete. The rcu critical section only guarantees
143 * no further reads against netdev_map. It does __not__ ensure pending
144 * flush operations (if any) are complete.
147 spin_lock(&dev_map_lock
);
148 list_del_rcu(&dtab
->list
);
149 spin_unlock(&dev_map_lock
);
153 /* To ensure all pending flush operations have completed wait for flush
154 * bitmap to indicate all flush_needed bits to be zero on _all_ cpus.
155 * Because the above synchronize_rcu() ensures the map is disconnected
156 * from the program we can assume no new bits will be set.
158 for_each_online_cpu(cpu
) {
159 unsigned long *bitmap
= per_cpu_ptr(dtab
->flush_needed
, cpu
);
161 while (!bitmap_empty(bitmap
, dtab
->map
.max_entries
))
165 for (i
= 0; i
< dtab
->map
.max_entries
; i
++) {
166 struct bpf_dtab_netdev
*dev
;
168 dev
= dtab
->netdev_map
[i
];
176 free_percpu(dtab
->flush_needed
);
177 bpf_map_area_free(dtab
->netdev_map
);
181 static int dev_map_get_next_key(struct bpf_map
*map
, void *key
, void *next_key
)
183 struct bpf_dtab
*dtab
= container_of(map
, struct bpf_dtab
, map
);
184 u32 index
= key
? *(u32
*)key
: U32_MAX
;
185 u32
*next
= next_key
;
187 if (index
>= dtab
->map
.max_entries
) {
192 if (index
== dtab
->map
.max_entries
- 1)
198 void __dev_map_insert_ctx(struct bpf_map
*map
, u32 bit
)
200 struct bpf_dtab
*dtab
= container_of(map
, struct bpf_dtab
, map
);
201 unsigned long *bitmap
= this_cpu_ptr(dtab
->flush_needed
);
203 __set_bit(bit
, bitmap
);
206 /* __dev_map_flush is called from xdp_do_flush_map() which _must_ be signaled
207 * from the driver before returning from its napi->poll() routine. The poll()
208 * routine is called either from busy_poll context or net_rx_action signaled
209 * from NET_RX_SOFTIRQ. Either way the poll routine must complete before the
210 * net device can be torn down. On devmap tear down we ensure the ctx bitmap
211 * is zeroed before completing to ensure all flush operations have completed.
213 void __dev_map_flush(struct bpf_map
*map
)
215 struct bpf_dtab
*dtab
= container_of(map
, struct bpf_dtab
, map
);
216 unsigned long *bitmap
= this_cpu_ptr(dtab
->flush_needed
);
219 for_each_set_bit(bit
, bitmap
, map
->max_entries
) {
220 struct bpf_dtab_netdev
*dev
= READ_ONCE(dtab
->netdev_map
[bit
]);
221 struct net_device
*netdev
;
223 /* This is possible if the dev entry is removed by user space
224 * between xdp redirect and flush op.
229 __clear_bit(bit
, bitmap
);
231 if (likely(netdev
->netdev_ops
->ndo_xdp_flush
))
232 netdev
->netdev_ops
->ndo_xdp_flush(netdev
);
236 /* rcu_read_lock (from syscall and BPF contexts) ensures that if a delete and/or
237 * update happens in parallel here a dev_put wont happen until after reading the
240 struct net_device
*__dev_map_lookup_elem(struct bpf_map
*map
, u32 key
)
242 struct bpf_dtab
*dtab
= container_of(map
, struct bpf_dtab
, map
);
243 struct bpf_dtab_netdev
*dev
;
245 if (key
>= map
->max_entries
)
248 dev
= READ_ONCE(dtab
->netdev_map
[key
]);
249 return dev
? dev
->dev
: NULL
;
252 static void *dev_map_lookup_elem(struct bpf_map
*map
, void *key
)
254 struct net_device
*dev
= __dev_map_lookup_elem(map
, *(u32
*)key
);
256 return dev
? &dev
->ifindex
: NULL
;
259 static void dev_map_flush_old(struct bpf_dtab_netdev
*dev
)
261 if (dev
->dev
->netdev_ops
->ndo_xdp_flush
) {
262 struct net_device
*fl
= dev
->dev
;
263 unsigned long *bitmap
;
266 for_each_online_cpu(cpu
) {
267 bitmap
= per_cpu_ptr(dev
->dtab
->flush_needed
, cpu
);
268 __clear_bit(dev
->bit
, bitmap
);
270 fl
->netdev_ops
->ndo_xdp_flush(dev
->dev
);
275 static void __dev_map_entry_free(struct rcu_head
*rcu
)
277 struct bpf_dtab_netdev
*dev
;
279 dev
= container_of(rcu
, struct bpf_dtab_netdev
, rcu
);
280 dev_map_flush_old(dev
);
285 static int dev_map_delete_elem(struct bpf_map
*map
, void *key
)
287 struct bpf_dtab
*dtab
= container_of(map
, struct bpf_dtab
, map
);
288 struct bpf_dtab_netdev
*old_dev
;
291 if (k
>= map
->max_entries
)
294 /* Use call_rcu() here to ensure any rcu critical sections have
295 * completed, but this does not guarantee a flush has happened
296 * yet. Because driver side rcu_read_lock/unlock only protects the
297 * running XDP program. However, for pending flush operations the
298 * dev and ctx are stored in another per cpu map. And additionally,
299 * the driver tear down ensures all soft irqs are complete before
300 * removing the net device in the case of dev_put equals zero.
302 old_dev
= xchg(&dtab
->netdev_map
[k
], NULL
);
304 call_rcu(&old_dev
->rcu
, __dev_map_entry_free
);
308 static int dev_map_update_elem(struct bpf_map
*map
, void *key
, void *value
,
311 struct bpf_dtab
*dtab
= container_of(map
, struct bpf_dtab
, map
);
312 struct net
*net
= current
->nsproxy
->net_ns
;
313 struct bpf_dtab_netdev
*dev
, *old_dev
;
315 u32 ifindex
= *(u32
*)value
;
317 if (unlikely(map_flags
> BPF_EXIST
))
319 if (unlikely(i
>= dtab
->map
.max_entries
))
321 if (unlikely(map_flags
== BPF_NOEXIST
))
327 dev
= kmalloc_node(sizeof(*dev
), GFP_ATOMIC
| __GFP_NOWARN
,
332 dev
->dev
= dev_get_by_index(net
, ifindex
);
342 /* Use call_rcu() here to ensure rcu critical sections have completed
343 * Remembering the driver side flush operation will happen before the
344 * net device is removed.
346 old_dev
= xchg(&dtab
->netdev_map
[i
], dev
);
348 call_rcu(&old_dev
->rcu
, __dev_map_entry_free
);
353 const struct bpf_map_ops dev_map_ops
= {
354 .map_alloc
= dev_map_alloc
,
355 .map_free
= dev_map_free
,
356 .map_get_next_key
= dev_map_get_next_key
,
357 .map_lookup_elem
= dev_map_lookup_elem
,
358 .map_update_elem
= dev_map_update_elem
,
359 .map_delete_elem
= dev_map_delete_elem
,
362 static int dev_map_notification(struct notifier_block
*notifier
,
363 ulong event
, void *ptr
)
365 struct net_device
*netdev
= netdev_notifier_info_to_dev(ptr
);
366 struct bpf_dtab
*dtab
;
370 case NETDEV_UNREGISTER
:
371 /* This rcu_read_lock/unlock pair is needed because
372 * dev_map_list is an RCU list AND to ensure a delete
373 * operation does not free a netdev_map entry while we
374 * are comparing it against the netdev being unregistered.
377 list_for_each_entry_rcu(dtab
, &dev_map_list
, list
) {
378 for (i
= 0; i
< dtab
->map
.max_entries
; i
++) {
379 struct bpf_dtab_netdev
*dev
, *odev
;
381 dev
= READ_ONCE(dtab
->netdev_map
[i
]);
383 dev
->dev
->ifindex
!= netdev
->ifindex
)
385 odev
= cmpxchg(&dtab
->netdev_map
[i
], dev
, NULL
);
388 __dev_map_entry_free
);
399 static struct notifier_block dev_map_notifier
= {
400 .notifier_call
= dev_map_notification
,
403 static int __init
dev_map_init(void)
405 register_netdevice_notifier(&dev_map_notifier
);
409 subsys_initcall(dev_map_init
);