Commit 46654159 authored by Yafang Shao's avatar Yafang Shao Committed by Andrii Nakryiko
Browse files

bpf: Add bits iterator 



Add three new kfuncs for the bits iterator:
- bpf_iter_bits_new
  Initialize a new bits iterator for a given memory area. Due to the
  limitation of bpf memalloc, the max number of words (8-byte units) that
  can be iterated over is limited to (4096 / 8).
- bpf_iter_bits_next
  Get the next bit in a bpf_iter_bits
- bpf_iter_bits_destroy
  Destroy a bpf_iter_bits

The bits iterator facilitates the iteration of the bits of a memory area,
such as cpumask. It can be used in any context and on any address.

Signed-off-by: default avatarYafang Shao <laoar.shao@gmail.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240517023034.48138-2-laoar.shao@gmail.com
parent fbe3e847

kernel/bpf/helpers.c

+119 −0
Original line number Diff line number Diff line
@@ -2744,6 +2744,122 @@ __bpf_kfunc void bpf_preempt_enable(void) 
	preempt_enable();

}



struct bpf_iter_bits {

	__u64 __opaque[2];

} __aligned(8);



struct bpf_iter_bits_kern {

	union {

		unsigned long *bits;

		unsigned long bits_copy;

	};

	u32 nr_bits;

	int bit;

} __aligned(8);



/**

 * bpf_iter_bits_new() - Initialize a new bits iterator for a given memory area

 * @it: The new bpf_iter_bits to be created

 * @unsafe_ptr__ign: A pointer pointing to a memory area to be iterated over

 * @nr_words: The size of the specified memory area, measured in 8-byte units.

 * Due to the limitation of memalloc, it can't be greater than 512.

 *

 * This function initializes a new bpf_iter_bits structure for iterating over

 * a memory area which is specified by the @unsafe_ptr__ign and @nr_words. It

 * copies the data of the memory area to the newly created bpf_iter_bits @it for

 * subsequent iteration operations.

 *

 * On success, 0 is returned. On failure, ERR is returned.

 */

__bpf_kfunc int

bpf_iter_bits_new(struct bpf_iter_bits *it, const u64 *unsafe_ptr__ign, u32 nr_words)

{

	struct bpf_iter_bits_kern *kit = (void *)it;

	u32 nr_bytes = nr_words * sizeof(u64);

	u32 nr_bits = BYTES_TO_BITS(nr_bytes);

	int err;



	BUILD_BUG_ON(sizeof(struct bpf_iter_bits_kern) != sizeof(struct bpf_iter_bits));

	BUILD_BUG_ON(__alignof__(struct bpf_iter_bits_kern) !=

		     __alignof__(struct bpf_iter_bits));



	kit->nr_bits = 0;

	kit->bits_copy = 0;

	kit->bit = -1;



	if (!unsafe_ptr__ign || !nr_words)

		return -EINVAL;



	/* Optimization for u64 mask */

	if (nr_bits == 64) {

		err = bpf_probe_read_kernel_common(&kit->bits_copy, nr_bytes, unsafe_ptr__ign);

		if (err)

			return -EFAULT;



		kit->nr_bits = nr_bits;

		return 0;

	}



	/* Fallback to memalloc */

	kit->bits = bpf_mem_alloc(&bpf_global_ma, nr_bytes);

	if (!kit->bits)

		return -ENOMEM;



	err = bpf_probe_read_kernel_common(kit->bits, nr_bytes, unsafe_ptr__ign);

	if (err) {

		bpf_mem_free(&bpf_global_ma, kit->bits);

		return err;

	}



	kit->nr_bits = nr_bits;

	return 0;

}



/**

 * bpf_iter_bits_next() - Get the next bit in a bpf_iter_bits

 * @it: The bpf_iter_bits to be checked

 *

 * This function returns a pointer to a number representing the value of the

 * next bit in the bits.

 *

 * If there are no further bits available, it returns NULL.

 */

__bpf_kfunc int *bpf_iter_bits_next(struct bpf_iter_bits *it)

{

	struct bpf_iter_bits_kern *kit = (void *)it;

	u32 nr_bits = kit->nr_bits;

	const unsigned long *bits;

	int bit;



	if (nr_bits == 0)

		return NULL;



	bits = nr_bits == 64 ? &kit->bits_copy : kit->bits;

	bit = find_next_bit(bits, nr_bits, kit->bit + 1);

	if (bit >= nr_bits) {

		kit->nr_bits = 0;

		return NULL;

	}



	kit->bit = bit;

	return &kit->bit;

}



/**

 * bpf_iter_bits_destroy() - Destroy a bpf_iter_bits

 * @it: The bpf_iter_bits to be destroyed

 *

 * Destroy the resource associated with the bpf_iter_bits.

 */

__bpf_kfunc void bpf_iter_bits_destroy(struct bpf_iter_bits *it)

{

	struct bpf_iter_bits_kern *kit = (void *)it;



	if (kit->nr_bits <= 64)

		return;

	bpf_mem_free(&bpf_global_ma, kit->bits);

}



__bpf_kfunc_end_defs();



BTF_KFUNCS_START(generic_btf_ids)
@@ -2826,6 +2942,9 @@ BTF_ID_FLAGS(func, bpf_wq_set_callback_impl) 
BTF_ID_FLAGS(func, bpf_wq_start)

BTF_ID_FLAGS(func, bpf_preempt_disable)

BTF_ID_FLAGS(func, bpf_preempt_enable)

BTF_ID_FLAGS(func, bpf_iter_bits_new, KF_ITER_NEW)

BTF_ID_FLAGS(func, bpf_iter_bits_next, KF_ITER_NEXT | KF_RET_NULL)

BTF_ID_FLAGS(func, bpf_iter_bits_destroy, KF_ITER_DESTROY)

BTF_KFUNCS_END(common_btf_ids)



static const struct btf_kfunc_id_set common_kfunc_set = {