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: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index aa6f8571de136b74fba93996883bd69b3e28d412..43ae40c8763e889c14892a29741674c32beeecbb 100644 (file)
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -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 {

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index c5b30fd8a3151f99b8cf175ad2a7ce563a0e13c8..2be5f6e8bb04a0580de3643be8851f5b21f816f7 100644 (file)
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -31,21 +31,27 @@ struct bpf_htab {
 struct htab_elem {
        struct hlist_node hash_node;
        struct rcu_head rcu;
-       u32 hash;
+       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);
+
+       /* 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;
 
-       l_new->hash = htab_map_hash(l_new->key, key_size);
-       b = __select_bucket(htab, l_new->hash);
+       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;
        }
 
@@ -352,7 +502,12 @@ 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);
-                       kfree(l);
+                       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);
+                       }
                }
        }
 }
@@ -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);