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bpf: Add bits iterator

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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: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240517023034.48138-2-laoar.shao@gmail.com
This commit is contained in:
Yafang Shao 2024-05-17 10:30:33 +08:00 committed by Andrii Nakryiko
parent fbe3e8473f
commit 4665415975
1 changed files with 119 additions and 0 deletions
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119
kernel/bpf/helpers.c
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@ -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 = {