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>

2 files changed, 363 insertions, 1 deletions

diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index 0daf7f6ae7df..2c0ec7f9da78 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -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
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
new file mode 100644
index 000000000000..d234a012f046
--- /dev/null
+++ b/kernel/bpf/hashtab.c
@@ -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);