linux-kernel - Re: [PATCH v4 3/7] arm64/Kconfig: add LSUI Kconfig

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Message-ID: <aH9JH6WSTLKNYgXS@e129823.arm.com>
Date: Tue, 22 Jul 2025 09:17:35 +0100
From: Yeoreum Yun <yeoreum.yun@....com>
To: Mark Rutland <mark.rutland@....com>
Cc: catalin.marinas@....com, will@...nel.org, broonie@...nel.org,
	oliver.upton@...ux.dev, ardb@...nel.org, frederic@...nel.org,
	james.morse@....com, joey.gouly@....com,
	scott@...amperecomputing.com, maz@...nel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/7] arm64/Kconfig: add LSUI Kconfig

Hi Mark,

> On Mon, Jul 21, 2025 at 09:36:14AM +0100, Yeoreum Yun wrote:
> > Since Armv9.6, FEAT_LSUI supplies the load/store instructions for
> > previleged level to access to access user memory without clearing
> > PSTATE.PAN bit.
> > It's enough to add CONFIG_AS_HAS_LSUI only because the code for LUSI uses
>
> Nit: s/LUSI/LSUI/
>
> > indiviual `.arch_extension` entries.
>
> Nit: s/indiviual/individual/

Sorry. I'll change it...


> > Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>
> > ---
> >  arch/arm64/Kconfig | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index 393d71124f5d..c0beb44ed5b8 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -2238,6 +2238,15 @@ config ARM64_GCS
> >
> >  endmenu # "v9.4 architectural features"
> >
> > +config AS_HAS_LSUI
> > +	def_bool $(as-instr,.arch_extension lsui)
> > +	help
> > +	 Unprivileged Load Store is an extension to introduce unprivileged
> > +	 variants of load and store instructions so that clearing PSTATE.PAN
> > +	 is never required in privileged mode.
> > +	 This feature is available with clang version 20 and later and not yet
> > +	 supported by gcc.
>
> I don't think we need to describe the feature in detail for the AS_HAS_*
> config symbol; I think all we need to say is:
>
> 	Supported by LLVM 20 and later, not yet supported by GNU AS.
>

Okay. I'll change it.

> Otherwise this looks fine.

Thanks!

[...]

--
Sincerely,
Yeoreum Yun