Re: [PATCH bpf-next v4 2/8] bpf: Introduce global percpu data

[Leon Hwang <leon.hwang@linux.dev>]

On Mon, 20 Apr 2026 07:58:06 -0700, "Alexei Starovoitov" <alexei.starovoitov@gmail.com> wrote:
> On Sun Apr 19, 2026 at 10:24 PM PDT, Leon Hwang wrote:
>>
>> int xdp_prog(struct xdp_md * ctx):
>> ; cnt++;
>> 0: (18) r6 = map[id:28][0]+0
>> 2: (bf) r6 = &(void __percpu *)(r6)
>
> well. that insn was inserted by the verifier and it shows up in xlated.
> That was expected.
> The point about 'bogus xlated' was about offset translation.
> map_direct_value_meta() should recover proper insns[i + 1].imm = off;
> In your example it's zero, so not an interesting test.
>

The original insns[i + 1] wasn't broken. See the key change of this
patch.

+			/*
+			 * Reuse the original ld_imm64 insn, and add one
+			 * mov64_percpu_reg insn.
+			 */
+
+			insn_buf[0] = insn[1];
+			insn_buf[1] = BPF_MOV64_PERCPU_REG(insn->dst_reg, insn->dst_reg);
+			cnt = 2;
+
+			i++;
+			new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
+			if (!new_prog)
+				return -ENOMEM;

So, it didn't touch the original ld_imm64 insn. That said, no bogus
xlated about offset translation.

>
[...]
>> @@ -6370,7 +6372,8 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
>> if (tnum_is_const(reg->var_off) &&
>> bpf_map_is_rdonly(map) &&
>> map->ops->map_direct_value_addr &&
>> -                           map->map_type != BPF_MAP_TYPE_INSN_ARRAY) {
>> +                           map->map_type != BPF_MAP_TYPE_INSN_ARRAY &&
>> +                           map->map_type != BPF_MAP_TYPE_PERCPU_ARRAY) {
>
> why add BPF_MAP_TYPE_PERCPU_ARRAY here?
>

After looking into bpf_map_is_rdonly(), yes, no need to add check for
percpu_array here.

Thanks,
Leon

>> int map_off = off + reg->var_off.value;
>> u64 val = 0;