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// 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.
*/
#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 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;
};
static DEFINE_SPINLOCK(dev_map_lock);
static LIST_HEAD(dev_map_list);
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 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;
return 0;
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);
}
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 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;
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