Commit 824bd0ce authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by David S. Miller
Browse files

bpf: introduce BPF_MAP_TYPE_PERCPU_HASH map 



Introduce BPF_MAP_TYPE_PERCPU_HASH map type which is used to do
accurate counters without need to use BPF_XADD instruction which turned
out to be too costly for high-performance network monitoring.
In the typical use case the 'key' is the flow tuple or other long
living object that sees a lot of events per second.

bpf_map_lookup_elem() returns per-cpu area.
Example:
struct {
  u32 packets;
  u32 bytes;
} * ptr = bpf_map_lookup_elem(&map, &key);
/* ptr points to this_cpu area of the value, so the following
 * increments will not collide with other cpus
 */
ptr->packets ++;
ptr->bytes += skb->len;

bpf_update_elem() atomically creates a new element where all per-cpu
values are zero initialized and this_cpu value is populated with
given 'value'.
Note that non-per-cpu hash map always allocates new element
and then deletes old after rcu grace period to maintain atomicity
of update. Per-cpu hash map updates element values in-place.

Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent ba905f5e

include/uapi/linux/bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -81,6 +81,7 @@ enum bpf_map_type { 
	BPF_MAP_TYPE_ARRAY,

	BPF_MAP_TYPE_PROG_ARRAY,

	BPF_MAP_TYPE_PERF_EVENT_ARRAY,

	BPF_MAP_TYPE_PERCPU_HASH,

};



enum bpf_prog_type {

kernel/bpf/hashtab.c

+228 −47
Original line number Diff line number Diff line
@@ -31,21 +31,27 @@ struct bpf_htab { 
struct htab_elem {

	struct hlist_node hash_node;

	struct rcu_head rcu;

	union {

		u32 hash;

		u32 key_size;

	};

	char key[0] __aligned(8);

};



/* Called from syscall */

static struct bpf_map *htab_map_alloc(union bpf_attr *attr)

{

	bool percpu = attr->map_type == BPF_MAP_TYPE_PERCPU_HASH;

	struct bpf_htab *htab;

	int err, i;

	u64 cost;



	htab = kzalloc(sizeof(*htab), GFP_USER);

	if (!htab)

		return ERR_PTR(-ENOMEM);



	/* mandatory map attributes */

	htab->map.map_type = attr->map_type;

	htab->map.key_size = attr->key_size;

	htab->map.value_size = attr->value_size;

	htab->map.max_entries = attr->max_entries;
@@ -77,24 +83,34 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr) 
		 */

		goto free_htab;



	if (percpu && round_up(htab->map.value_size, 8) > PCPU_MIN_UNIT_SIZE)

		/* make sure the size for pcpu_alloc() is reasonable */

		goto free_htab;



	htab->elem_size = sizeof(struct htab_elem) +

			  round_up(htab->map.key_size, 8) +

			  htab->map.value_size;

			  round_up(htab->map.key_size, 8);

	if (percpu)

		htab->elem_size += sizeof(void *);

	else

		htab->elem_size += htab->map.value_size;



	/* prevent zero size kmalloc and check for u32 overflow */

	if (htab->n_buckets == 0 ||

	    htab->n_buckets > U32_MAX / sizeof(struct bucket))

		goto free_htab;



	if ((u64) htab->n_buckets * sizeof(struct bucket) +

	    (u64) htab->elem_size * htab->map.max_entries >=

	    U32_MAX - PAGE_SIZE)

	cost = (u64) htab->n_buckets * sizeof(struct bucket) +

	       (u64) htab->elem_size * htab->map.max_entries;



	if (percpu)

		cost += (u64) round_up(htab->map.value_size, 8) *

			num_possible_cpus() * htab->map.max_entries;



	if (cost >= U32_MAX - PAGE_SIZE)

		/* make sure page count doesn't overflow */

		goto free_htab;



	htab->map.pages = round_up(htab->n_buckets * sizeof(struct bucket) +

				   htab->elem_size * htab->map.max_entries,

				   PAGE_SIZE) >> PAGE_SHIFT;

	htab->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;



	err = -ENOMEM;

	htab->buckets = kmalloc_array(htab->n_buckets, sizeof(struct bucket),
@@ -148,7 +164,7 @@ static struct htab_elem *lookup_elem_raw(struct hlist_head *head, u32 hash, 
}



/* Called from syscall or from eBPF program */

static void *htab_map_lookup_elem(struct bpf_map *map, void *key)

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;
@@ -166,6 +182,13 @@ static void *htab_map_lookup_elem(struct bpf_map *map, void *key) 


	l = lookup_elem_raw(head, hash, key, key_size);



	return l;

}



static void *htab_map_lookup_elem(struct bpf_map *map, void *key)

{

	struct htab_elem *l = __htab_map_lookup_elem(map, key);



	if (l)

		return l->key + round_up(map->key_size, 8);
@@ -230,65 +253,139 @@ find_first_elem: 
	return -ENOENT;

}





static inline void htab_elem_set_ptr(struct htab_elem *l, u32 key_size,

				     void __percpu *pptr)

{

	*(void __percpu **)(l->key + key_size) = pptr;

}



static inline void __percpu *htab_elem_get_ptr(struct htab_elem *l, u32 key_size)

{

	return *(void __percpu **)(l->key + key_size);

}



static void htab_percpu_elem_free(struct htab_elem *l)

{

	free_percpu(htab_elem_get_ptr(l, l->key_size));

	kfree(l);

}



static void htab_percpu_elem_free_rcu(struct rcu_head *head)

{

	struct htab_elem *l = container_of(head, struct htab_elem, rcu);



	htab_percpu_elem_free(l);

}



static void free_htab_elem(struct htab_elem *l, bool percpu, u32 key_size)

{

	if (percpu) {

		l->key_size = key_size;

		call_rcu(&l->rcu, htab_percpu_elem_free_rcu);

	} else {

		kfree_rcu(l, rcu);

	}

}



static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,

					 void *value, u32 key_size, u32 hash,

					 bool percpu)

{

	u32 size = htab->map.value_size;

	struct htab_elem *l_new;

	void __percpu *pptr;



	l_new = kmalloc(htab->elem_size, GFP_ATOMIC | __GFP_NOWARN);

	if (!l_new)

		return NULL;



	memcpy(l_new->key, key, key_size);

	if (percpu) {

		/* round up value_size to 8 bytes */

		size = round_up(size, 8);



		/* alloc_percpu zero-fills */

		pptr = __alloc_percpu_gfp(size, 8, GFP_ATOMIC | __GFP_NOWARN);

		if (!pptr) {

			kfree(l_new);

			return NULL;

		}



		/* copy true value_size bytes */

		memcpy(this_cpu_ptr(pptr), value, htab->map.value_size);

		htab_elem_set_ptr(l_new, key_size, pptr);

	} else {

		memcpy(l_new->key + round_up(key_size, 8), value, size);

	}



	l_new->hash = hash;

	return l_new;

}



static int check_flags(struct bpf_htab *htab, struct htab_elem *l_old,

		       u64 map_flags)

{

	if (!l_old && unlikely(atomic_read(&htab->count) >= htab->map.max_entries))

		/* if elem with this 'key' doesn't exist and we've reached

		 * max_entries limit, fail insertion of new elem

		 */

		return -E2BIG;



	if (l_old && map_flags == BPF_NOEXIST)

		/* elem already exists */

		return -EEXIST;



	if (!l_old && map_flags == BPF_EXIST)

		/* elem doesn't exist, cannot update it */

		return -ENOENT;



	return 0;

}



/* 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 htab_elem *l_new = NULL, *l_old;

	struct hlist_head *head;

	struct bucket *b;

	unsigned long flags;

	u32 key_size;

	struct bucket *b;

	u32 key_size, hash;

	int ret;



	if (map_flags > BPF_EXIST)

	if (unlikely(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 | __GFP_NOWARN);

	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);

	hash = htab_map_hash(key, key_size);



	l_new->hash = htab_map_hash(l_new->key, key_size);

	b = __select_bucket(htab, l_new->hash);

	/* allocate new element outside of the lock, since

	 * we're most likley going to insert it

	 */

	l_new = alloc_htab_elem(htab, key, value, key_size, hash, false);

	if (!l_new)

		return -ENOMEM;



	b = __select_bucket(htab, hash);

	head = &b->head;



	/* bpf_map_update_elem() can be called in_irq() */

	raw_spin_lock_irqsave(&b->lock, flags);



	l_old = lookup_elem_raw(head, l_new->hash, key, key_size);

	l_old = lookup_elem_raw(head, hash, key, key_size);



	if (!l_old && unlikely(atomic_read(&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;

	ret = check_flags(htab, l_old, map_flags);

	if (ret)

		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

	/* 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) {
@@ -298,7 +395,6 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value, 
		atomic_inc(&htab->count);

	}

	raw_spin_unlock_irqrestore(&b->lock, flags);



	return 0;

err:

	raw_spin_unlock_irqrestore(&b->lock, flags);
@@ -306,10 +402,64 @@ err: 
	return ret;

}



static int htab_percpu_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 = NULL, *l_old;

	struct hlist_head *head;

	unsigned long flags;

	struct bucket *b;

	u32 key_size, hash;

	int ret;



	if (unlikely(map_flags > BPF_EXIST))

		/* unknown flags */

		return -EINVAL;



	WARN_ON_ONCE(!rcu_read_lock_held());



	key_size = map->key_size;



	hash = htab_map_hash(key, key_size);



	b = __select_bucket(htab, hash);

	head = &b->head;



	/* bpf_map_update_elem() can be called in_irq() */

	raw_spin_lock_irqsave(&b->lock, flags);



	l_old = lookup_elem_raw(head, hash, key, key_size);



	ret = check_flags(htab, l_old, map_flags);

	if (ret)

		goto err;



	if (l_old) {

		/* per-cpu hash map can update value in-place */

		memcpy(this_cpu_ptr(htab_elem_get_ptr(l_old, key_size)),

		       value, htab->map.value_size);

	} else {

		l_new = alloc_htab_elem(htab, key, value, key_size,

					hash, true);

		if (!l_new) {

			ret = -ENOMEM;

			goto err;

		}

		hlist_add_head_rcu(&l_new->hash_node, head);

		atomic_inc(&htab->count);

	}

	ret = 0;

err:

	raw_spin_unlock_irqrestore(&b->lock, flags);

	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);

	bool percpu = map->map_type == BPF_MAP_TYPE_PERCPU_HASH;

	struct hlist_head *head;

	struct bucket *b;

	struct htab_elem *l;
@@ -332,7 +482,7 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key) 
	if (l) {

		hlist_del_rcu(&l->hash_node);

		atomic_dec(&htab->count);

		kfree_rcu(l, rcu);

		free_htab_elem(l, percpu, key_size);

		ret = 0;

	}
@@ -352,10 +502,15 @@ static void delete_all_elements(struct bpf_htab *htab) 
		hlist_for_each_entry_safe(l, n, head, hash_node) {

			hlist_del_rcu(&l->hash_node);

			atomic_dec(&htab->count);

			if (htab->map.map_type == BPF_MAP_TYPE_PERCPU_HASH) {

				l->key_size = htab->map.key_size;

				htab_percpu_elem_free(l);

			} else {

				kfree(l);

			}

		}

	}

}



/* Called when map->refcnt goes to zero, either from workqueue or from syscall */

static void htab_map_free(struct bpf_map *map)
@@ -391,9 +546,35 @@ static struct bpf_map_type_list htab_type __read_mostly = { 
	.type = BPF_MAP_TYPE_HASH,

};



/* Called from eBPF program */

static void *htab_percpu_map_lookup_elem(struct bpf_map *map, void *key)

{

	struct htab_elem *l = __htab_map_lookup_elem(map, key);



	if (l)

		return this_cpu_ptr(htab_elem_get_ptr(l, map->key_size));

	else

		return NULL;

}



static const struct bpf_map_ops htab_percpu_ops = {

	.map_alloc = htab_map_alloc,

	.map_free = htab_map_free,

	.map_get_next_key = htab_map_get_next_key,

	.map_lookup_elem = htab_percpu_map_lookup_elem,

	.map_update_elem = htab_percpu_map_update_elem,

	.map_delete_elem = htab_map_delete_elem,

};



static struct bpf_map_type_list htab_percpu_type __read_mostly = {

	.ops = &htab_percpu_ops,

	.type = BPF_MAP_TYPE_PERCPU_HASH,

};



static int __init register_htab_map(void)

{

	bpf_register_map_type(&htab_type);

	bpf_register_map_type(&htab_percpu_type);

	return 0;

}

late_initcall(register_htab_map);

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