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: <07707b44fc9032398db551041498d6265ccf0a0313ecd8779bd1fa82a7d96409@mail.kernel.org>
Date: Wed, 26 Nov 2025 15:11:40 +0000 (UTC)
From: bot+bpf-ci@...nel.org
To: leon.hwang@...ux.dev,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,leon.hwang@...ux.dev,kernel-patches-bot@...com,linux-kernel@...r.kernel.org,linux-kselftest@...r.kernel.org,ast@...nel.org,andrii@...nel.org,daniel@...earbox.net,martin.lau@...nel.org,eddyz87@...il.com,yonghong.song@...ux.dev,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

> 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))
                              ^^

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