On Sun, May 5, 2024 at 8:35 PM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
>
> 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 bits 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@xxxxxxxxx>
> ---
> kernel/bpf/helpers.c | 140 +++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 140 insertions(+)
>
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 2a69a9a36c0f..83b2a02f795f 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -2744,6 +2744,143 @@ __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 ponter pointing to a memory area to be iterated over
typo: pointer
> + * @nr_bits: The number of bits to be iterated over. Due to the limitation of
> + * memalloc, it can't greater than (4096 * 8).
typo: can't be greater
> + *
> + * 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_bits. It
> + * copy the data of the memory area to the newly created bpf_iter_bits @it for
s/copy/copies/
> + * 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 void *unsafe_ptr__ign, u32 nr_bits)
> +{
> + struct bpf_iter_bits_kern *kit = (void *)it;
> + u32 words = BITS_TO_LONGS(nr_bits);
> + u32 size = BITS_TO_BYTES(nr_bits);
> + u32 left, offset;
> + 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));
> +
> + if (!unsafe_ptr__ign || !nr_bits) {
> + kit->bits = NULL;
> + return -EINVAL;
> + }
> +
> + kit->nr_bits = 0;
> + kit->bits_copy = 0;
> + /* Optimization for u64/u32 mask */
> + if (nr_bits <= 64) {
> + /* For big-endian, we must calculate the offset */
> + offset = IS_ENABLED(CONFIG_S390) ? sizeof(u64) - size : 0;
S390 isn't the only big-endian architecture, it's wrong to hard-code just S390
there is __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ check throughout the
kernel to do this detection
> +
> + err = bpf_probe_read_kernel_common(((char *)&kit->bits_copy) + offset,
> + size, unsafe_ptr__ign);
> + if (err)
> + return -EFAULT;
I'd rewrite the above to something like (not tested, but should give
the right idea):
long bits = 0;
err = bpf_probe_read_kernel_common(&bits, size, unsafe_ptr__ign);
if (err)
return -EFAULT;
#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
bits = __swab64(bits);
#endif
/* deal with bit mask of weird size, ensuring upper bits are zero */
bits <<= 64 - nr_bits;
bits >>= 64 - nr_bits;
kit->bits_copy = bits;
This should take care of both big-endianness, and non-multiple-of-8
sized bitmasks (I think, we need tests).
pw-bot: cr
> +
> + kit->nr_bits = nr_bits;
> + kit->bit = -1;
> + return 0;
> + }
> +
> + /* Fallback to memalloc */
> + kit->bits = bpf_mem_alloc(&bpf_global_ma, size);
> + if (!kit->bits)
> + return -ENOMEM;
> +
> + err = bpf_probe_read_kernel_common(kit->bits, words * sizeof(u64), unsafe_ptr__ign);
> + if (err) {
> + bpf_mem_free(&bpf_global_ma, kit->bits);
> + return err;
> + }
> +
> + /* long-aligned */
> + left = size & (sizeof(u64) - 1);
> + if (!left)
> + goto out;
> +
> + offset = IS_ENABLED(CONFIG_S390) ? sizeof(u64) - left : 0;
> + err = bpf_probe_read_kernel_common((char *)(kit->bits + words - 1) + offset, left,
> + unsafe_ptr__ign + (words - 1) * sizeof(u64));
> + if (err) {
> + bpf_mem_free(&bpf_global_ma, kit->bits);
> + return err;
> + }
tbh, I'm not sure what's the desired behavior here is. David (cc'ed),
you were dealing with cpumasks, how is the bit mask specified there?
Is it considered to be an long[] array or byte[] array? And how is
that working on big-endian, because I think it makes a difference?
Please take a look, thanks.
> +
> +out:
> + kit->nr_bits = nr_bits;
> + kit->bit = -1;
> + 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 bit 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 +2963,9 @@ 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 = {
> --
> 2.30.1 (Apple Git-130)
>
