On Fri, Mar 29, 2024 at 11:47 AM Andrii Nakryiko <andrii@xxxxxxxxxx> wrote:
>
> Using new per-CPU BPF instruction, partially inline
> bpf_map_lookup_elem() helper for per-CPU hashmap BPF map. Just like for
> normal HASH map, we still generate a call into __htab_map_lookup_elem(),
> but after that we resolve per-CPU element address using a new
> instruction, saving on extra functions calls.
>
> Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> ---
> kernel/bpf/hashtab.c | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
>
> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
> index e81059faae63..74950f373bab 100644
> --- a/kernel/bpf/hashtab.c
> +++ b/kernel/bpf/hashtab.c
> @@ -2308,6 +2308,26 @@ static void *htab_percpu_map_lookup_elem(struct bpf_map *map, void *key)
> return NULL;
> }
>
> +/* inline bpf_map_lookup_elem() call for per-CPU hashmap */
> +static int htab_percpu_map_gen_lookup(struct bpf_map *map, struct bpf_insn *insn_buf)
> +{
> + struct bpf_insn *insn = insn_buf;
> +
> + if (!bpf_jit_supports_percpu_insns())
> + return -EOPNOTSUPP;
> +
> + BUILD_BUG_ON(!__same_type(&__htab_map_lookup_elem,
> + (void *(*)(struct bpf_map *map, void *key))NULL));
> + *insn++ = BPF_EMIT_CALL(__htab_map_lookup_elem);
> + *insn++ = BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 3);
> + *insn++ = BPF_ALU64_IMM(BPF_ADD, BPF_REG_0,
> + offsetof(struct htab_elem, key) + map->key_size);
> + *insn++ = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, 0);
here and in the previous patch probably need to gate this by
sizeof(void *) == 8
Just to prevent future bugs.
> + *insn++ = BPF_LDX_ADDR_PERCPU(BPF_REG_0, BPF_REG_0, 0);
Overall it looks great!
