linux-kernel - Re: [PATCH -next v20 20/26] riscv: Add prctl controls for userspace vector management

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Date:   Tue, 30 May 2023 22:14:16 +0800
From:   Andy Chiu <andy.chiu@...ive.com>
To:     Rémi Denis-Courmont <remi@...lab.net>
Cc:     palmer@...belt.com, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next v20 20/26] riscv: Add prctl controls for userspace
 vector management

On Thu, May 25, 2023 at 12:16 AM Rémi Denis-Courmont <remi@...lab.net> wrote:
>
> Le keskiviikkona 24. toukokuuta 2023, 12.25.30 EEST Andy Chiu a écrit :
> > How about adding the following 2 patches to deal with the problem.
> > However, I am concerned if this makes ELF_HWCAP too complicated. e.g.
> > Future extensions may as well want to do something here after we create
> > an entry here.
>
> Fine with me but I feel that we are missing the bigger picture here, as to
> what the usage pattern/guideline for the prctl() on userspace side should be?

Yes, I agree the use of this prctl is only meaningful for the init
system, or some ansenstor processes that make policy decisions. And
with ELF_HWCAP reflecting per-process's availability of V, which is
decided by either the prctl/sysctl, programs/libraries do not really
need to call this prctl unless they are doing aforementioned stuffs.

I am going to document these when rolling out the next revision.

>
> Maybe it was already discussed, and I just missed it, but I couldn't find it in
> the documentation.

We had discussed the potential theoretical abi breakage[1], and came
out with a need of a prctl/sysctl interface for distro's early
userspace programs.

>
> --
> Rémi Denis-Courmont
> http://www.remlab.net/
>
>
>

[1]:https://lore.kernel.org/all/mhng-47aa965a-2b25-4ac0-984a-c2e6f3a051ee@palmer-ri-x1c9/

Thanks,
Andy