linux-kernel - Re: [PATCH v2] riscv: Add sysctl to control discard of vstate during syscall

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Message-ID: <aJrVHenvkMTRYcsS@x1>
Date: Mon, 11 Aug 2025 22:46:05 -0700
From: Drew Fustini <fustini@...nel.org>
To: Vivian Wang <wangruikang@...as.ac.cn>
Cc: Darius Rad <darius@...espec.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Alexandre Ghiti <alex@...ti.fr>,
	Samuel Holland <samuel.holland@...ive.com>,
	Björn Töpel <bjorn@...osinc.com>,
	Andy Chiu <andybnac@...il.com>,
	Conor Dooley <conor.dooley@...rochip.com>,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Drew Fustini <dfustini@...storrent.com>
Subject: Re: [PATCH v2] riscv: Add sysctl to control discard of vstate during
 syscall

On Sun, Aug 10, 2025 at 05:52:54PM +0800, Vivian Wang wrote:
> >   Discarding vector state on syscall entry can help identify userpace
> >   programs that are mistakenly relying on vector state being preserved
> >   across syscalls. This can be useful for debugging and test suites.
> >   However, this behavior can negatively impact performance on some
> >   RISC-V implementations.
> >
> >   Say Y here if you want mandatory clobbering of vector state before
> >   entering all syscalls. If you select N, then userspace can still
> >   eanble it via the abi.riscv_v_vstate_discard sysctl knob.
> 
> Typo: eanble -> enable
> 
> Also, I think it kinda makes the false impression that the sysctl knob
> is only available with this set to N? I think this should be structured
> to say something like this being the default value, and also say that
> userspace can override this behavior system-wide via the sysctl knob.

Thanks, that is a good point that I should clarify that the user can
still override via the sysctl knob regardless of whether choosing Y or N
for this Kconfig option.

-Drew