linux-kernel - Re: [PATCH] kselftest/arm64: abi: fix SVCR detection

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Message-ID: <3279e669-1ee2-4792-9e10-8b40928de6b4@sirena.org.uk>
Date: Mon, 9 Dec 2024 12:36:52 +0000
From: Mark Brown <broonie@...nel.org>
To: Weizhao Ouyang <o451686892@...il.com>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Shuah Khan <shuah@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kselftest/arm64: abi: fix SVCR detection

On Mon, Dec 09, 2024 at 06:52:37PM +0800, Weizhao Ouyang wrote:

> When using svcr_in to check ZA and Streaming Mode, we should make sure
> that the value in x2 is correct, otherwise it may trigger an Illegal
> instruction if FEAT_SVE and !FEAT_SME.

>  	// Set SVCR if we're doing SME
> -	cbz	x1, 1f
>  	adrp	x2, svcr_in
>  	ldr	x2, [x2, :lo12:svcr_in]
> +	cbz	x1, 1f
>  	msr	S3_3_C4_C2_2, x2

This is against an older verison of the code so wouldn't apply now.
It's not also checking the value of SVCR, this is checking the SME flag
passed in via x1.  You can see that the SVCR value is loaded into x2 but
the check is against x1.

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