Commit 05799638 authored by Yonghong Song's avatar Yonghong Song Committed by Alexei Starovoitov
Browse files

bpf: Add batch ops to all htab bpf map 

htab can't use generic batch support due some problematic behaviours
inherent to the data structre, i.e. while iterating the bpf map  a
concurrent program might delete the next entry that batch was about to
use, in that case there's no easy solution to retrieve the next entry,
the issue has been discussed multiple times (see [1] and [2]).

The only way hmap can be traversed without the problem previously
exposed is by making sure that the map is traversing entire buckets.
This commit implements those strict requirements for hmap, the
implementation follows the same interaction that generic support with
some exceptions:

 - If keys/values buffer are not big enough to traverse a bucket,
   ENOSPC will be returned.
 - out_batch contains the value of the next bucket in the iteration, not
   the next key, but this is transparent for the user since the user
   should never use out_batch for other than bpf batch syscalls.

This commits implements BPF_MAP_LOOKUP_BATCH and adds support for new
command BPF_MAP_LOOKUP_AND_DELETE_BATCH. Note that for update/delete
batch ops it is possible to use the generic implementations.

[1] https://lore.kernel.org/bpf/20190724165803.87470-1-brianvv@google.com/
[2] https://lore.kernel.org/bpf/20190906225434.3635421-1-yhs@fb.com/



Signed-off-by: default avatarYonghong Song <yhs@fb.com>
Signed-off-by: default avatarBrian Vazquez <brianvv@google.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200115184308.162644-6-brianvv@google.com
parent c60f2d28

include/linux/bpf.h

+3 −0
Original line number Diff line number Diff line
@@ -46,6 +46,9 @@ struct bpf_map_ops { 
	void *(*map_lookup_elem_sys_only)(struct bpf_map *map, void *key);

	int (*map_lookup_batch)(struct bpf_map *map, const union bpf_attr *attr,

				union bpf_attr __user *uattr);

	int (*map_lookup_and_delete_batch)(struct bpf_map *map,

					   const union bpf_attr *attr,

					   union bpf_attr __user *uattr);

	int (*map_update_batch)(struct bpf_map *map, const union bpf_attr *attr,

				union bpf_attr __user *uattr);

	int (*map_delete_batch)(struct bpf_map *map, const union bpf_attr *attr,

include/uapi/linux/bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -108,6 +108,7 @@ enum bpf_cmd { 
	BPF_MAP_FREEZE,

	BPF_BTF_GET_NEXT_ID,

	BPF_MAP_LOOKUP_BATCH,

	BPF_MAP_LOOKUP_AND_DELETE_BATCH,

	BPF_MAP_UPDATE_BATCH,

	BPF_MAP_DELETE_BATCH,

};

kernel/bpf/hashtab.c

+264 −0
Original line number Diff line number Diff line
@@ -17,6 +17,16 @@ 
	(BPF_F_NO_PREALLOC | BPF_F_NO_COMMON_LRU | BPF_F_NUMA_NODE |	\

	 BPF_F_ACCESS_MASK | BPF_F_ZERO_SEED)



#define BATCH_OPS(_name)			\

	.map_lookup_batch =			\

	_name##_map_lookup_batch,		\

	.map_lookup_and_delete_batch =		\

	_name##_map_lookup_and_delete_batch,	\

	.map_update_batch =			\

	generic_map_update_batch,		\

	.map_delete_batch =			\

	generic_map_delete_batch



struct bucket {

	struct hlist_nulls_head head;

	raw_spinlock_t lock;
@@ -1232,6 +1242,256 @@ static void htab_map_seq_show_elem(struct bpf_map *map, void *key, 
	rcu_read_unlock();

}



static int

__htab_map_lookup_and_delete_batch(struct bpf_map *map,

				   const union bpf_attr *attr,

				   union bpf_attr __user *uattr,

				   bool do_delete, bool is_lru_map,

				   bool is_percpu)

{

	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);

	u32 bucket_cnt, total, key_size, value_size, roundup_key_size;

	void *keys = NULL, *values = NULL, *value, *dst_key, *dst_val;

	void __user *uvalues = u64_to_user_ptr(attr->batch.values);

	void __user *ukeys = u64_to_user_ptr(attr->batch.keys);

	void *ubatch = u64_to_user_ptr(attr->batch.in_batch);

	u32 batch, max_count, size, bucket_size;

	u64 elem_map_flags, map_flags;

	struct hlist_nulls_head *head;

	struct hlist_nulls_node *n;

	unsigned long flags;

	struct htab_elem *l;

	struct bucket *b;

	int ret = 0;



	elem_map_flags = attr->batch.elem_flags;

	if ((elem_map_flags & ~BPF_F_LOCK) ||

	    ((elem_map_flags & BPF_F_LOCK) && !map_value_has_spin_lock(map)))

		return -EINVAL;



	map_flags = attr->batch.flags;

	if (map_flags)

		return -EINVAL;



	max_count = attr->batch.count;

	if (!max_count)

		return 0;



	if (put_user(0, &uattr->batch.count))

		return -EFAULT;



	batch = 0;

	if (ubatch && copy_from_user(&batch, ubatch, sizeof(batch)))

		return -EFAULT;



	if (batch >= htab->n_buckets)

		return -ENOENT;



	key_size = htab->map.key_size;

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

	value_size = htab->map.value_size;

	size = round_up(value_size, 8);

	if (is_percpu)

		value_size = size * num_possible_cpus();

	total = 0;

	/* while experimenting with hash tables with sizes ranging from 10 to

	 * 1000, it was observed that a bucket can have upto 5 entries.

	 */

	bucket_size = 5;



alloc:

	/* We cannot do copy_from_user or copy_to_user inside

	 * the rcu_read_lock. Allocate enough space here.

	 */

	keys = kvmalloc(key_size * bucket_size, GFP_USER | __GFP_NOWARN);

	values = kvmalloc(value_size * bucket_size, GFP_USER | __GFP_NOWARN);

	if (!keys || !values) {

		ret = -ENOMEM;

		goto after_loop;

	}



again:

	preempt_disable();

	this_cpu_inc(bpf_prog_active);

	rcu_read_lock();

again_nocopy:

	dst_key = keys;

	dst_val = values;

	b = &htab->buckets[batch];

	head = &b->head;

	raw_spin_lock_irqsave(&b->lock, flags);



	bucket_cnt = 0;

	hlist_nulls_for_each_entry_rcu(l, n, head, hash_node)

		bucket_cnt++;



	if (bucket_cnt > (max_count - total)) {

		if (total == 0)

			ret = -ENOSPC;

		raw_spin_unlock_irqrestore(&b->lock, flags);

		rcu_read_unlock();

		this_cpu_dec(bpf_prog_active);

		preempt_enable();

		goto after_loop;

	}



	if (bucket_cnt > bucket_size) {

		bucket_size = bucket_cnt;

		raw_spin_unlock_irqrestore(&b->lock, flags);

		rcu_read_unlock();

		this_cpu_dec(bpf_prog_active);

		preempt_enable();

		kvfree(keys);

		kvfree(values);

		goto alloc;

	}



	hlist_nulls_for_each_entry_safe(l, n, head, hash_node) {

		memcpy(dst_key, l->key, key_size);



		if (is_percpu) {

			int off = 0, cpu;

			void __percpu *pptr;



			pptr = htab_elem_get_ptr(l, map->key_size);

			for_each_possible_cpu(cpu) {

				bpf_long_memcpy(dst_val + off,

						per_cpu_ptr(pptr, cpu), size);

				off += size;

			}

		} else {

			value = l->key + roundup_key_size;

			if (elem_map_flags & BPF_F_LOCK)

				copy_map_value_locked(map, dst_val, value,

						      true);

			else

				copy_map_value(map, dst_val, value);

			check_and_init_map_lock(map, dst_val);

		}

		if (do_delete) {

			hlist_nulls_del_rcu(&l->hash_node);

			if (is_lru_map)

				bpf_lru_push_free(&htab->lru, &l->lru_node);

			else

				free_htab_elem(htab, l);

		}

		dst_key += key_size;

		dst_val += value_size;

	}



	raw_spin_unlock_irqrestore(&b->lock, flags);

	/* If we are not copying data, we can go to next bucket and avoid

	 * unlocking the rcu.

	 */

	if (!bucket_cnt && (batch + 1 < htab->n_buckets)) {

		batch++;

		goto again_nocopy;

	}



	rcu_read_unlock();

	this_cpu_dec(bpf_prog_active);

	preempt_enable();

	if (bucket_cnt && (copy_to_user(ukeys + total * key_size, keys,

	    key_size * bucket_cnt) ||

	    copy_to_user(uvalues + total * value_size, values,

	    value_size * bucket_cnt))) {

		ret = -EFAULT;

		goto after_loop;

	}



	total += bucket_cnt;

	batch++;

	if (batch >= htab->n_buckets) {

		ret = -ENOENT;

		goto after_loop;

	}

	goto again;



after_loop:

	if (ret == -EFAULT)

		goto out;



	/* copy # of entries and next batch */

	ubatch = u64_to_user_ptr(attr->batch.out_batch);

	if (copy_to_user(ubatch, &batch, sizeof(batch)) ||

	    put_user(total, &uattr->batch.count))

		ret = -EFAULT;



out:

	kvfree(keys);

	kvfree(values);

	return ret;

}



static int

htab_percpu_map_lookup_batch(struct bpf_map *map, const union bpf_attr *attr,

			     union bpf_attr __user *uattr)

{

	return __htab_map_lookup_and_delete_batch(map, attr, uattr, false,

						  false, true);

}



static int

htab_percpu_map_lookup_and_delete_batch(struct bpf_map *map,

					const union bpf_attr *attr,

					union bpf_attr __user *uattr)

{

	return __htab_map_lookup_and_delete_batch(map, attr, uattr, true,

						  false, true);

}



static int

htab_map_lookup_batch(struct bpf_map *map, const union bpf_attr *attr,

		      union bpf_attr __user *uattr)

{

	return __htab_map_lookup_and_delete_batch(map, attr, uattr, false,

						  false, false);

}



static int

htab_map_lookup_and_delete_batch(struct bpf_map *map,

				 const union bpf_attr *attr,

				 union bpf_attr __user *uattr)

{

	return __htab_map_lookup_and_delete_batch(map, attr, uattr, true,

						  false, false);

}



static int

htab_lru_percpu_map_lookup_batch(struct bpf_map *map,

				 const union bpf_attr *attr,

				 union bpf_attr __user *uattr)

{

	return __htab_map_lookup_and_delete_batch(map, attr, uattr, false,

						  true, true);

}



static int

htab_lru_percpu_map_lookup_and_delete_batch(struct bpf_map *map,

					    const union bpf_attr *attr,

					    union bpf_attr __user *uattr)

{

	return __htab_map_lookup_and_delete_batch(map, attr, uattr, true,

						  true, true);

}



static int

htab_lru_map_lookup_batch(struct bpf_map *map, const union bpf_attr *attr,

			  union bpf_attr __user *uattr)

{

	return __htab_map_lookup_and_delete_batch(map, attr, uattr, false,

						  true, false);

}



static int

htab_lru_map_lookup_and_delete_batch(struct bpf_map *map,

				     const union bpf_attr *attr,

				     union bpf_attr __user *uattr)

{

	return __htab_map_lookup_and_delete_batch(map, attr, uattr, true,

						  true, false);

}



const struct bpf_map_ops htab_map_ops = {

	.map_alloc_check = htab_map_alloc_check,

	.map_alloc = htab_map_alloc,
@@ -1242,6 +1502,7 @@ const struct bpf_map_ops htab_map_ops = { 
	.map_delete_elem = htab_map_delete_elem,

	.map_gen_lookup = htab_map_gen_lookup,

	.map_seq_show_elem = htab_map_seq_show_elem,

	BATCH_OPS(htab),

};



const struct bpf_map_ops htab_lru_map_ops = {
@@ -1255,6 +1516,7 @@ const struct bpf_map_ops htab_lru_map_ops = { 
	.map_delete_elem = htab_lru_map_delete_elem,

	.map_gen_lookup = htab_lru_map_gen_lookup,

	.map_seq_show_elem = htab_map_seq_show_elem,

	BATCH_OPS(htab_lru),

};



/* Called from eBPF program */
@@ -1368,6 +1630,7 @@ const struct bpf_map_ops htab_percpu_map_ops = { 
	.map_update_elem = htab_percpu_map_update_elem,

	.map_delete_elem = htab_map_delete_elem,

	.map_seq_show_elem = htab_percpu_map_seq_show_elem,

	BATCH_OPS(htab_percpu),

};



const struct bpf_map_ops htab_lru_percpu_map_ops = {
@@ -1379,6 +1642,7 @@ const struct bpf_map_ops htab_lru_percpu_map_ops = { 
	.map_update_elem = htab_lru_percpu_map_update_elem,

	.map_delete_elem = htab_lru_map_delete_elem,

	.map_seq_show_elem = htab_percpu_map_seq_show_elem,

	BATCH_OPS(htab_lru_percpu),

};



static int fd_htab_map_alloc_check(union bpf_attr *attr)

kernel/bpf/syscall.c

+8 −1
Original line number Diff line number Diff line
@@ -3310,7 +3310,8 @@ static int bpf_map_do_batch(const union bpf_attr *attr, 
	if (IS_ERR(map))

		return PTR_ERR(map);



	if (cmd == BPF_MAP_LOOKUP_BATCH &&

	if ((cmd == BPF_MAP_LOOKUP_BATCH ||

	     cmd == BPF_MAP_LOOKUP_AND_DELETE_BATCH) &&

	    !(map_get_sys_perms(map, f) & FMODE_CAN_READ)) {

		err = -EPERM;

		goto err_put;
@@ -3324,6 +3325,8 @@ static int bpf_map_do_batch(const union bpf_attr *attr, 


	if (cmd == BPF_MAP_LOOKUP_BATCH)

		BPF_DO_BATCH(map->ops->map_lookup_batch);

	else if (cmd == BPF_MAP_LOOKUP_AND_DELETE_BATCH)

		BPF_DO_BATCH(map->ops->map_lookup_and_delete_batch);

	else if (cmd == BPF_MAP_UPDATE_BATCH)

		BPF_DO_BATCH(map->ops->map_update_batch);

	else
@@ -3434,6 +3437,10 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz 
	case BPF_MAP_LOOKUP_BATCH:

		err = bpf_map_do_batch(&attr, uattr, BPF_MAP_LOOKUP_BATCH);

		break;

	case BPF_MAP_LOOKUP_AND_DELETE_BATCH:

		err = bpf_map_do_batch(&attr, uattr,

				       BPF_MAP_LOOKUP_AND_DELETE_BATCH);

		break;

	case BPF_MAP_UPDATE_BATCH:

		err = bpf_map_do_batch(&attr, uattr, BPF_MAP_UPDATE_BATCH);

		break;

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