linux-kernel - Re: [PATCH v2 0/3] arm64/sme: Support disabling streaming mode via ptrace on SME only systems

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Message-ID: <87ms4fmjpq.fsf@linaro.org>
Date: Fri, 21 Nov 2025 13:30:41 -0300
From: Thiago Jung Bauermann <thiago.bauermann@...aro.org>
To: Luis <luis.machado.foss@...il.com>
Cc: Catalin Marinas <cmarinas@...nel.org>,  Will Deacon <will@...nel.org>,
  Shuah Khan <shuah@...nel.org>,  Jonathan Corbet <corbet@....net>,  Oleg
 Nesterov <oleg@...hat.com>,  Mark Brown <broonie@...nel.org>,  Catalin
 Marinas <catalin.marinas@....com>,  Mark Rutland <mark.rutland@....com>,
  David Spickett <david.spickett@....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 v2 0/3] arm64/sme: Support disabling streaming mode via
 ptrace on SME only systems

Luis <luis.machado.foss@...il.com> writes:

> [off-list, as I'm having bouncing issues]
>
> Hi,
>
> On 17/11/2025 21:00, Catalin Marinas wrote:
>> From: Catalin Marinas <catalin.marinas@....com>
>> On Wed, 15 Oct 2025 18:56:35 +0100, Mark Brown wrote:
>>> Currently it is not possible to disable streaming mode via ptrace on SME
>>> only systems, the interface for doing this is to write via NT_ARM_SVE but
>>> such writes will be rejected on a system without SVE support. Enable this
>>> functionality by allowing userspace to write SVE_PT_REGS_FPSIMD format data
>>> via NT_ARM_SVE with the vector length set to 0 on SME only systems. Such
>>> writes currently error since we require that a vector length is specified
>>> which should minimise the risk that existing software is relying on current
>>> behaviour.
>>>
>>> [...]
>> I don't think we'll get gdb feedback soon. Thanks David for the LLDB
>> ack.
>
> Unfortunately this flew under the radar for me, and I haven´t been following these
> discussions closely.
>
> Is there someone working to rectify/validate this in GDB from Arm's side?
>
> I´d gladly review it and get it through into upstream gdb.

I will work on it next week.

-- 
Thiago