linux-kernel - Re: [RFC PATCH 1/1] arch: arm64: Implement unaligned atomic emulation

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Message-ID: <aQzKjZci6kgMTziA@finisterre.sirena.org.uk>
Date: Thu, 6 Nov 2025 16:19:25 +0000
From: Mark Brown <broonie@...nel.org>
To: André Almeida <andrealmeid@...lia.com>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kernel-dev@...lia.com, Ryan Houdek <houdek.ryan@...-emu.org>,
	Billy Laws <blaws05@...il.com>
Subject: Re: [RFC PATCH 1/1] arch: arm64: Implement unaligned atomic emulation

On Thu, Nov 06, 2025 at 01:07:35PM -0300, André Almeida wrote:

> +int set_unalign_atomic_ctl(unsigned int val)
> +{
> +	unsigned long valid_mask = PR_ARM64_UNALIGN_ATOMIC_EMULATE;
> +	if (val & ~valid_mask)
> +		return -EINVAL;
> +
> +	/*
> +	 * TODO: check if this is running in a ARM v8.1 or greater.
> +	 * Refuse otherwise.
> +	 */

The code should check for the specific feature you're relying on, not
the architecture level which isn't really a technically discoverable
thing, something like:

	if (!cpus_have_final_cap(ARM64_HAS_LDAPR))
		return -EINVAL;

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