From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Yafang Shao <laoar.shao@gmail.com>
Cc: ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com,
andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com,
song@kernel.org, yonghong.song@linux.dev, kpsingh@kernel.org,
sdf@google.com, haoluo@google.com, jolsa@kernel.org,
bpf@vger.kernel.org
Subject: Re: [PATCH v2 bpf-next 1/2] bpf: Add bits iterator
Date: Tue, 27 Feb 2024 17:24:22 -0800 [thread overview]
Message-ID: <CAEf4BzZfUnV+k6kGo1+JDhhQ1SOnTJ84M-0GVn0m66z9d6DiqQ@mail.gmail.com> (raw)
In-Reply-To: <20240225100637.48394-2-laoar.shao@gmail.com>
On Sun, Feb 25, 2024 at 2:07 AM Yafang Shao <laoar.shao@gmail.com> 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@gmail.com>
> ---
> kernel/bpf/helpers.c | 100 +++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 100 insertions(+)
>
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 93edf730d288..052f63891834 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -2542,6 +2542,103 @@ __bpf_kfunc void bpf_throw(u64 cookie)
> WARN(1, "A call to BPF exception callback should never return\n");
> }
>
> +struct bpf_iter_bits {
> + __u64 __opaque[2];
> +} __aligned(8);
> +
> +struct bpf_iter_bits_kern {
> + unsigned long *bits;
> + 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
> + * @nr_bits: The number of bits to be iterated over. Due to the limitation of
> + * memalloc, it can't greater than (4096 * 8).
> + *
> + * 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
> + * 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 size = BITS_TO_BYTES(nr_bits);
> + 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->bits = bpf_mem_alloc(&bpf_global_ma, size);
> + if (!kit->bits)
> + return -ENOMEM;
it's probably going to be a pretty common case to do bits iteration
for nr_bits<=64, right? So as an optimization, instead of doing
bpf_mem_alloc() for this case, you can just copy up to 8 bytes and
store it in a union of `unsigned long *bits` and `unsigned long
bits_copy`. As a performance optimization (and to reduce dependency on
memory allocation). WDYT?
> +
> + err = bpf_probe_read_kernel_common(kit->bits, size, unsafe_ptr__ign);
> + if (err) {
> + bpf_mem_free(&bpf_global_ma, kit->bits);
> + kit->bits = NULL;
> + return err;
> + }
> +
> + 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;
> + const unsigned long *bits = kit->bits;
> + int bit;
> +
> + if (!bits)
> + return NULL;
> +
> + bit = find_next_bit(bits, kit->nr_bits, kit->bit + 1);
> + if (bit >= kit->nr_bits)
> + 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->bits)
> + return;
> + bpf_mem_free(&bpf_global_ma, kit->bits);
> +}
> +
> __bpf_kfunc_end_defs();
>
> BTF_KFUNCS_START(generic_btf_ids)
> @@ -2618,6 +2715,9 @@ BTF_ID_FLAGS(func, bpf_dynptr_is_null)
> BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly)
> BTF_ID_FLAGS(func, bpf_dynptr_size)
> BTF_ID_FLAGS(func, bpf_dynptr_clone)
> +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 = {
> --
> 2.39.1
>
next prev parent reply other threads:[~2024-02-28 1:24 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-25 10:06 [PATCH v2 bpf-next 0/2] bpf: Add a generic bits iterator Yafang Shao
2024-02-25 10:06 ` [PATCH v2 bpf-next 1/2] bpf: Add " Yafang Shao
2024-02-28 1:24 ` Andrii Nakryiko [this message]
2024-02-28 2:25 ` Yafang Shao
2024-02-28 6:04 ` Andrii Nakryiko
2024-02-29 2:15 ` Yafang Shao
2024-02-29 17:26 ` Andrii Nakryiko
2024-02-29 22:19 ` John Fastabend
2024-03-01 6:40 ` Yafang Shao
2024-03-01 18:01 ` John Fastabend
2024-02-25 10:06 ` [PATCH v2 bpf-next 2/2] selftests/bpf: Add selftest for bits iter Yafang Shao
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