/* 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/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;
unsigned long int __percpu *flush_needed;
struct list_head list;
};
static DEFINE_SPINLOCK(dev_map_lock);
static LIST_HEAD(dev_map_list);
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);
err = -ENOMEM;
/* make sure page count doesn't overflow */
cost = (u64) dtab->map.max_entries * sizeof(struct bpf_dtab_netdev *);
cost += BITS_TO_LONGS(attr->max_entries) * sizeof(unsigned long);
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(
BITS_TO_LONGS(attr->max_entries) *
sizeof(unsigned long),
__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(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.
*/
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();
}
/* Although we should no longer have datapath or bpf syscall operations
* at this point we we can still race with netdev notifier, hence the
* lock.
*/
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
*/
spin_lock(&dev_map_lock);
list_del_rcu(&dtab->list);
spin_unlock(&dev_map_lock);
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 = (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;
}
void __dev_map_insert_ctx(struct bpf_map *map, u32 key)
{
struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
unsigned long *bitmap = this_cpu_ptr(dtab->flush_needed);
__set_bit(key, bitmap);
}
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;
}
/* __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;
netdev = dev->dev;
__clear_bit(bit, bitmap);
if (unlikely(!netdev || !netdev->netdev_ops->ndo_xdp_flush))
continue;
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.
*/
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_flush_old(struct bpf_dtab_netdev *old_dev)
{
if (old_dev->dev->netdev_ops->ndo_xdp_flush) {
struct net_device *fl = old_dev->dev;
unsigned long *bitmap;
int cpu;
for_each_online_cpu(cpu) {
bitmap = per_cpu_ptr(old_dev->dtab->flush_needed, cpu);
__clear_bit(old_dev->key, bitmap);
fl->netdev_ops->ndo_xdp_flush(old_dev->dev);
}
}
}
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_map_flush_old(old_dev);
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_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->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,
};
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);
