linux-kernel - Re: [PATCH 3/5] arm64/sme: Support disabling streaming mode via ptrace on SME only systems

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Message-ID: <4b691bb8-c047-4546-9ab2-c9a183a10dc8@infradead.org>
Date: Wed, 20 Aug 2025 11:39:18 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: Mark Brown <broonie@...nel.org>, Catalin Marinas
 <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Shuah Khan <shuah@...nel.org>, Jonathan Corbet <corbet@....net>,
 Oleg Nesterov <oleg@...hat.com>
Cc: Mark Rutland <mark.rutland@....com>,
 David Spickett <david.spickett@....com>,
 Thiago Jung Bauermann <thiago.bauermann@...aro.org>,
 Luis Machado <luis.machado.foss@...il.com>,
 linux-arm-kernel@...ts.infradead.org, linux-kselftest@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH 3/5] arm64/sme: Support disabling streaming mode via
 ptrace on SME only systems



On 8/20/25 11:29 AM, Mark Brown wrote:
> diff --git a/Documentation/arch/arm64/sve.rst b/Documentation/arch/arm64/sve.rst
> index 28152492c29c..a61c9d0efe4d 100644
> --- a/Documentation/arch/arm64/sve.rst
> +++ b/Documentation/arch/arm64/sve.rst
> @@ -402,6 +402,11 @@ The regset data starts with struct user_sve_header, containing:
>    streaming mode and any SETREGSET of NT_ARM_SSVE will enter streaming mode
>    if the target was not in streaming mode.
>  
> +* On systems that do not support SVE it is permitted to use SETREGSET to
> +  write SVE_PT_REGS_FPSIMD formatted data via NT_ARM_SVE, in this case the

s/,/;/
or
                                                 NT_ARM_SVE. In this case

> +  vector length should be specified as 0. This allows streaming mode to be
> +  disabled on systems with SME but not SVE.
> +
>  * If any register data is provided along with SVE_PT_VL_ONEXEC then the
>    registers data will be interpreted with the current vector length, not
>    the vector length configured for use on exec.

-- 
~Randy