linux-kernel - Re: [PATCH] arm64/ptrace: Don't flush ZA/ZT storage when writing ZA via ptrace

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Date: Thu, 18 Jan 2024 12:02:24 +0000
From: Will Deacon <will@...nel.org>
To: Oleg Nesterov <oleg@...hat.com>,
	Mark Brown <broonie@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>
Cc: kernel-team@...roid.com,
	Will Deacon <will@...nel.org>,
	linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Dave Martin <dave.martin@....com>
Subject: Re: [PATCH] arm64/ptrace: Don't flush ZA/ZT storage when writing ZA via ptrace

On Mon, 15 Jan 2024 18:42:38 +0000, Mark Brown wrote:
> When writing ZA we currently unconditionally flush the buffer used to store
> it as part of ensuring that it is allocated. Since this buffer is shared
> with ZT0 this means that a write to ZA when PSTATE.ZA is already set will
> corrupt the value of ZT0 on a SME2 system. Fix this by only flushing the
> backing storage if PSTATE.ZA was not previously set.
> 
> This will mean that short or failed writes may leave stale data in the
> buffer, this seems as correct as our current behaviour and unlikely to be
> something that userspace will rely on.
> 
> [...]

Applied to arm64 (for-next/core), thanks!

[1/1] arm64/ptrace: Don't flush ZA/ZT storage when writing ZA via ptrace
      https://git.kernel.org/arm64/c/b7c510d04904

Cheers,
-- 
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev