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bpf: add hashtable type of eBPF maps

add new map type BPF_MAP_TYPE_HASH and its implementation

- maps are created/destroyed by userspace. Both userspace and eBPF programs
  can lookup/update/delete elements from the map

- eBPF programs can be called in_irq(), so use spin_lock_irqsave() mechanism
  for concurrent updates

- key/value are opaque range of bytes (aligned to 8 bytes)

- user space provides 3 configuration attributes via BPF syscall:
  key_size, value_size, max_entries

- map takes care of allocating/freeing key/value pairs

- map_update_elem() must fail to insert new element when max_entries
  limit is reached to make sure that eBPF programs cannot exhaust memory

- map_update_elem() replaces elements in an atomic way

- optimized for speed of lookup() which can be called multiple times from
  eBPF program which itself is triggered by high volume of events
  . in the future JIT compiler may recognize lookup() call and optimize it
    further, since key_size is constant for life of eBPF program

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Alexei Starovoitov authored and davem330 committed Nov 14, 2014
1 parent 3274f52 commit 0f8e4bd8a1fc8c4185f1630061d0a1f2d197a475
Showing with 364 additions and 1 deletion.
  1. +1 −0 include/uapi/linux/bpf.h
  2. +1 −1 kernel/bpf/Makefile
  3. +362 −0 kernel/bpf/hashtab.c
@@ -111,6 +111,7 @@ enum bpf_cmd {
enum bpf_map_type {
BPF_MAP_TYPE_UNSPEC,
BPF_MAP_TYPE_HASH,
};
enum bpf_prog_type {
@@ -1,5 +1,5 @@
obj-y := core.o
obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o
obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o hashtab.o
ifdef CONFIG_TEST_BPF
obj-$(CONFIG_BPF_SYSCALL) += test_stub.o
endif
@@ -0,0 +1,362 @@
/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
*
* 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.
*/
#include <linux/bpf.h>
#include <linux/jhash.h>
#include <linux/filter.h>
#include <linux/vmalloc.h>
struct bpf_htab {
struct bpf_map map;
struct hlist_head *buckets;
spinlock_t lock;
u32 count; /* number of elements in this hashtable */
u32 n_buckets; /* number of hash buckets */
u32 elem_size; /* size of each element in bytes */
};
/* each htab element is struct htab_elem + key + value */
struct htab_elem {
struct hlist_node hash_node;
struct rcu_head rcu;
u32 hash;
char key[0] __aligned(8);
};
/* Called from syscall */
static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
{
struct bpf_htab *htab;
int err, i;
htab = kzalloc(sizeof(*htab), GFP_USER);
if (!htab)
return ERR_PTR(-ENOMEM);
/* mandatory map attributes */
htab->map.key_size = attr->key_size;
htab->map.value_size = attr->value_size;
htab->map.max_entries = attr->max_entries;
/* check sanity of attributes.
* value_size == 0 may be allowed in the future to use map as a set
*/
err = -EINVAL;
if (htab->map.max_entries == 0 || htab->map.key_size == 0 ||
htab->map.value_size == 0)
goto free_htab;
/* hash table size must be power of 2 */
htab->n_buckets = roundup_pow_of_two(htab->map.max_entries);
err = -E2BIG;
if (htab->map.key_size > MAX_BPF_STACK)
/* eBPF programs initialize keys on stack, so they cannot be
* larger than max stack size
*/
goto free_htab;
err = -ENOMEM;
htab->buckets = kmalloc_array(htab->n_buckets, sizeof(struct hlist_head),
GFP_USER | __GFP_NOWARN);
if (!htab->buckets) {
htab->buckets = vmalloc(htab->n_buckets * sizeof(struct hlist_head));
if (!htab->buckets)
goto free_htab;
}
for (i = 0; i < htab->n_buckets; i++)
INIT_HLIST_HEAD(&htab->buckets[i]);
spin_lock_init(&htab->lock);
htab->count = 0;
htab->elem_size = sizeof(struct htab_elem) +
round_up(htab->map.key_size, 8) +
htab->map.value_size;
return &htab->map;
free_htab:
kfree(htab);
return ERR_PTR(err);
}
static inline u32 htab_map_hash(const void *key, u32 key_len)
{
return jhash(key, key_len, 0);
}
static inline struct hlist_head *select_bucket(struct bpf_htab *htab, u32 hash)
{
return &htab->buckets[hash & (htab->n_buckets - 1)];
}
static struct htab_elem *lookup_elem_raw(struct hlist_head *head, u32 hash,
void *key, u32 key_size)
{
struct htab_elem *l;
hlist_for_each_entry_rcu(l, head, hash_node)
if (l->hash == hash && !memcmp(&l->key, key, key_size))
return l;
return NULL;
}
/* Called from syscall or from eBPF program */
static void *htab_map_lookup_elem(struct bpf_map *map, void *key)
{
struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
struct hlist_head *head;
struct htab_elem *l;
u32 hash, key_size;
/* Must be called with rcu_read_lock. */
WARN_ON_ONCE(!rcu_read_lock_held());
key_size = map->key_size;
hash = htab_map_hash(key, key_size);
head = select_bucket(htab, hash);
l = lookup_elem_raw(head, hash, key, key_size);
if (l)
return l->key + round_up(map->key_size, 8);
return NULL;
}
/* Called from syscall */
static int htab_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
{
struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
struct hlist_head *head;
struct htab_elem *l, *next_l;
u32 hash, key_size;
int i;
WARN_ON_ONCE(!rcu_read_lock_held());
key_size = map->key_size;
hash = htab_map_hash(key, key_size);
head = select_bucket(htab, hash);
/* lookup the key */
l = lookup_elem_raw(head, hash, key, key_size);
if (!l) {
i = 0;
goto find_first_elem;
}
/* key was found, get next key in the same bucket */
next_l = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(&l->hash_node)),
struct htab_elem, hash_node);
if (next_l) {
/* if next elem in this hash list is non-zero, just return it */
memcpy(next_key, next_l->key, key_size);
return 0;
}
/* no more elements in this hash list, go to the next bucket */
i = hash & (htab->n_buckets - 1);
i++;
find_first_elem:
/* iterate over buckets */
for (; i < htab->n_buckets; i++) {
head = select_bucket(htab, i);
/* pick first element in the bucket */
next_l = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),
struct htab_elem, hash_node);
if (next_l) {
/* if it's not empty, just return it */
memcpy(next_key, next_l->key, key_size);
return 0;
}
}
/* itereated over all buckets and all elements */
return -ENOENT;
}
/* Called from syscall or from eBPF program */
static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
u64 map_flags)
{
struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
struct htab_elem *l_new, *l_old;
struct hlist_head *head;
unsigned long flags;
u32 key_size;
int ret;
if (map_flags > BPF_EXIST)
/* unknown flags */
return -EINVAL;
WARN_ON_ONCE(!rcu_read_lock_held());
/* allocate new element outside of lock */
l_new = kmalloc(htab->elem_size, GFP_ATOMIC);
if (!l_new)
return -ENOMEM;
key_size = map->key_size;
memcpy(l_new->key, key, key_size);
memcpy(l_new->key + round_up(key_size, 8), value, map->value_size);
l_new->hash = htab_map_hash(l_new->key, key_size);
/* bpf_map_update_elem() can be called in_irq() */
spin_lock_irqsave(&htab->lock, flags);
head = select_bucket(htab, l_new->hash);
l_old = lookup_elem_raw(head, l_new->hash, key, key_size);
if (!l_old && unlikely(htab->count >= map->max_entries)) {
/* if elem with this 'key' doesn't exist and we've reached
* max_entries limit, fail insertion of new elem
*/
ret = -E2BIG;
goto err;
}
if (l_old && map_flags == BPF_NOEXIST) {
/* elem already exists */
ret = -EEXIST;
goto err;
}
if (!l_old && map_flags == BPF_EXIST) {
/* elem doesn't exist, cannot update it */
ret = -ENOENT;
goto err;
}
/* add new element to the head of the list, so that concurrent
* search will find it before old elem
*/
hlist_add_head_rcu(&l_new->hash_node, head);
if (l_old) {
hlist_del_rcu(&l_old->hash_node);
kfree_rcu(l_old, rcu);
} else {
htab->count++;
}
spin_unlock_irqrestore(&htab->lock, flags);
return 0;
err:
spin_unlock_irqrestore(&htab->lock, flags);
kfree(l_new);
return ret;
}
/* Called from syscall or from eBPF program */
static int htab_map_delete_elem(struct bpf_map *map, void *key)
{
struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
struct hlist_head *head;
struct htab_elem *l;
unsigned long flags;
u32 hash, key_size;
int ret = -ENOENT;
WARN_ON_ONCE(!rcu_read_lock_held());
key_size = map->key_size;
hash = htab_map_hash(key, key_size);
spin_lock_irqsave(&htab->lock, flags);
head = select_bucket(htab, hash);
l = lookup_elem_raw(head, hash, key, key_size);
if (l) {
hlist_del_rcu(&l->hash_node);
htab->count--;
kfree_rcu(l, rcu);
ret = 0;
}
spin_unlock_irqrestore(&htab->lock, flags);
return ret;
}
static void delete_all_elements(struct bpf_htab *htab)
{
int i;
for (i = 0; i < htab->n_buckets; i++) {
struct hlist_head *head = select_bucket(htab, i);
struct hlist_node *n;
struct htab_elem *l;
hlist_for_each_entry_safe(l, n, head, hash_node) {
hlist_del_rcu(&l->hash_node);
htab->count--;
kfree(l);
}
}
}
/* Called when map->refcnt goes to zero, either from workqueue or from syscall */
static void htab_map_free(struct bpf_map *map)
{
struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
/* 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
*/
synchronize_rcu();
/* some of kfree_rcu() callbacks for elements of this map may not have
* executed. It's ok. Proceed to free residual elements and map itself
*/
delete_all_elements(htab);
kvfree(htab->buckets);
kfree(htab);
}
static struct bpf_map_ops htab_ops = {
.map_alloc = htab_map_alloc,
.map_free = htab_map_free,
.map_get_next_key = htab_map_get_next_key,
.map_lookup_elem = htab_map_lookup_elem,
.map_update_elem = htab_map_update_elem,
.map_delete_elem = htab_map_delete_elem,
};
static struct bpf_map_type_list tl = {
.ops = &htab_ops,
.type = BPF_MAP_TYPE_HASH,
};
static int __init register_htab_map(void)
{
bpf_register_map_type(&tl);
return 0;
}
late_initcall(register_htab_map);

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