netdev - Re: [PATCH net v4] bpf, net: Check cgroup_bpf_enabled() only once in do_sock

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Message-ID: <CAADnVQLvbMRvCg2disV+_AR-154BwRpeB8Zg_8YpO=7gzL=Trg@mail.gmail.com>
Date: Thu, 22 Aug 2024 09:00:35 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Tze-nan Wu (吳澤南) <Tze-nan.Wu@...iatek.com>, 
	Stanislav Fomichev <sdf@...ichev.me>
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	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "bpf@...r.kernel.org" <bpf@...r.kernel.org>, 
	"kuniyu@...zon.com" <kuniyu@...zon.com>, 
	"linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>, "ast@...nel.org" <ast@...nel.org>, 
	Cheng-Jui Wang (王正睿) <Cheng-Jui.Wang@...iatek.com>, 
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Subject: Re: [PATCH net v4] bpf, net: Check cgroup_bpf_enabled() only once in do_sock_getsockopt()

On Thu, Aug 22, 2024 at 12:02 AM Tze-nan Wu (吳澤南)
<Tze-nan.Wu@...iatek.com> wrote:
>
>
> BTW, If this should be handled in kernel, modification shown below
> could fix the issue without breaking the "static_branch" usage in both
> macros:
>
>
> +++ /include/linux/bpf-cgroup.h:
>     -#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen)
>     +#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen, compat)
>      ({
>             int __ret = 0;
>             if (cgroup_bpf_enabled(CGROUP_GETSOCKOPT))
>                 copy_from_sockptr(&__ret, optlen, sizeof(int));
>      +      else
>      +          *compat = true;
>             __ret;
>      })
>
>     #define BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock, level, optname,
> optval, optlen, max_optlen, retval)
>      ({
>          int __ret = retval;
>     -    if (cgroup_bpf_enabled(CGROUP_GETSOCKOPT) &&
>     -        cgroup_bpf_sock_enabled(sock, CGROUP_GETSOCKOPT))
>     +    if (cgroup_bpf_sock_enabled(sock, CGROUP_GETSOCKOPT))
>              if (!(sock)->sk_prot->bpf_bypass_getsockopt ||
>                ...
>
>   +++ /net/socket.c:
>     int do_sock_getsockopt(struct socket *sock, bool compat, int level,
>      {
>         ...
>         ...
>     +     /* The meaning of `compat` variable could be changed here
>     +      * to indicate if cgroup_bpf_enabled(CGROUP_SOCK_OPS) is
> false.
>     +      */
>         if (!compat)
>     -       max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen);
>     +       max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen,
> &compat);

This is better, but it's still quite a hack. Let's not override it.
We can have another bool, but the question:
do we really need BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN  ?
copy_from_sockptr(&__ret, optlen, sizeof(int));
should be fast enough to do it unconditionally.
What are we saving here?

Stan ?


>
> > Thanks,
> > --tze-nan
>
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