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

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Message-ID: <aH4b4G2DSxG5FnHb@J2N7QTR9R3>
Date: Mon, 21 Jul 2025 11:52:16 +0100
From: Mark Rutland <mark.rutland@....com>
To: Yeoreum Yun <yeoreum.yun@....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

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/

> 
> 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.

Otherwise this looks fine.

Mark.

> +
>  config ARM64_SVE
>  	bool "ARM Scalable Vector Extension support"
>  	default y
> -- 
> LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}
> 
>