linux-kernel - Re: [PATCH bpf-next v12 2/7] bpf: Add BPF_F_CPU and BPF_F_ALL_CPUS flags support for percpu

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Message-ID: <4d8120f7-f3b6-4654-9b14-0ee7da5f87ac@linux.dev>
Date: Wed, 26 Nov 2025 23:24:09 +0800
From: Leon Hwang <leon.hwang@...ux.dev>
To: bot+bpf-ci@...nel.org, bpf@...r.kernel.org
Cc: ast@...nel.org, andrii@...nel.org, daniel@...earbox.net,
 jolsa@...nel.org, yonghong.song@...ux.dev, song@...nel.org,
 eddyz87@...il.com, dxu@...uu.xyz, deso@...teo.net, martin.lau@...ux.dev,
 john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me,
 haoluo@...gle.com, shuah@...nel.org, kerneljasonxing@...il.com,
 chen.dylane@...ux.dev, willemb@...gle.com, paul.chaignon@...il.com,
 a.s.protopopov@...il.com, memxor@...il.com, yatsenko@...a.com,
 tklauser@...tanz.ch, kernel-patches-bot@...com,
 linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
 martin.lau@...nel.org, clm@...a.com, ihor.solodrai@...ux.dev
Subject: Re: [PATCH bpf-next v12 2/7] bpf: Add BPF_F_CPU and BPF_F_ALL_CPUS
 flags support for percpu_array maps



On 2025/11/26 23:11, bot+bpf-ci@...nel.org wrote:
>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>> index d84af3719..01a99e3a3 100644
>> --- a/include/linux/bpf.h
>> +++ b/include/linux/bpf.h
> 
> [ ... ]
> 
>> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
>> index 1eeb31c5b..67e9e811d 100644
>> --- a/kernel/bpf/arraymap.c
>> +++ b/kernel/bpf/arraymap.c
> 
> [ ... ]
> 
>> @@ -398,10 +405,11 @@ int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value,
>>  	struct bpf_array *array = container_of(map, struct bpf_array, map);
>>  	u32 index = *(u32 *)key;
>>  	void __percpu *pptr;
>> -	int cpu, off = 0;
>> +	void *ptr, *val;
>>  	u32 size;
>> +	int cpu;
>>
>> -	if (unlikely(map_flags > BPF_EXIST))
>> +	if (unlikely((map_flags & BPF_F_LOCK) || (u32)map_flags > BPF_F_ALL_CPUS))
>>  		/* unknown flags */
>>  		return -EINVAL;
>>
>> @@ -409,7 +417,7 @@ int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value,
>>  		/* all elements were pre-allocated, cannot insert a new one */
>>  		return -E2BIG;
>>
>> -	if (unlikely(map_flags & BPF_NOEXIST))
>> +	if (unlikely(map_flags == BPF_NOEXIST))
>                               ^^
> 

?

No such change in this version.

It seems that this change was inferred from v11 to v12 by AI itself.

Thanks,
Leon

> Does changing this from bitwise-AND to equality break flag combination
> handling? The old code checked (map_flags & BPF_NOEXIST), which would
> trigger for any flag combination including BPF_NOEXIST. The new code only
> checks (map_flags == BPF_NOEXIST), so if userspace passes
> (BPF_F_CPU | BPF_NOEXIST), the BPF_NOEXIST flag gets silently ignored
> instead of returning -EEXIST as before.
> 
> While all elements in percpu_array maps are pre-allocated and BPF_NOEXIST
> should always fail anyway, silently ignoring a flag the user explicitly set
> seems inconsistent with the principle of rejecting invalid flag combinations
> at validation time.
> 
>>  		/* all elements already exist */
>>  		return -EEXIST;
>>
> 
> [ ... ]
> 
> 
> ---
> AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
> See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
> 
> CI run summary: https://github.com/kernel-patches/bpf/actions/runs/19708012130