linux-kernel - Re: [PATCH bpf-next] bpf: Allow to use kfunc XDP hints and frags together

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Date:   Thu, 14 Sep 2023 09:29:57 -0700
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Larysa Zaremba <larysa.zaremba@...el.com>
Cc:     bpf@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>,
        Yonghong Song <yonghong.song@...ux.dev>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
        Jiri Olsa <jolsa@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next] bpf: Allow to use kfunc XDP hints and frags together

On 09/14, Larysa Zaremba wrote:
> There is no fundamental reason, why multi-buffer XDP and XDP kfunc RX hints
> cannot coexist in a single program.
> 
> Allow those features to be used together by modifying the flags conditions.
> 
> Suggested-by: Stanislav Fomichev <sdf@...gle.com>
> Link: https://lore.kernel.org/bpf/CAKH8qBuzgtJj=OKMdsxEkyML36VsAuZpcrsXcyqjdKXSJCBq=Q@mail.gmail.com/
> Signed-off-by: Larysa Zaremba <larysa.zaremba@...el.com>
> ---
>  kernel/bpf/offload.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/offload.c b/kernel/bpf/offload.c
> index ee35f33a96d1..43aded96c79b 100644
> --- a/kernel/bpf/offload.c
> +++ b/kernel/bpf/offload.c
> @@ -232,7 +232,11 @@ int bpf_prog_dev_bound_init(struct bpf_prog *prog, union bpf_attr *attr)
>  	    attr->prog_type != BPF_PROG_TYPE_XDP)
>  		return -EINVAL;
>  
> -	if (attr->prog_flags & ~BPF_F_XDP_DEV_BOUND_ONLY)
> +	if (attr->prog_flags & ~(BPF_F_XDP_DEV_BOUND_ONLY | BPF_F_XDP_HAS_FRAGS))
> +		return -EINVAL;
> +

[..]

> +	if (attr->prog_flags & BPF_F_XDP_HAS_FRAGS &&
> +	    !(attr->prog_flags & BPF_F_XDP_DEV_BOUND_ONLY))
>  		return -EINVAL;

Any reason we have 'attr->prog_flags & BPF_F_XDP_HAS_FRAGS' part here?
Seems like doing '!(attr->prog_flags & BPF_F_XDP_DEV_BOUND_ONLY)' should
be enough, right? We only want to bail out here when BPF_F_XDP_DEV_BOUND_ONLY
is not set and we don't really care whether BPF_F_XDP_HAS_FRAGS is set
or not at this point.