linux-kernel - Re: [PATCH AUTOSEL 5.10 2/6] x86/cpu: Don't clear X86_FEATURE_LAHF_LM flag in init_amd_k8() on AMD when running in a virtual machine

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Message-ID: <aAKDyGpzNOCdGmN2@duo.ucw.cz>
Date: Fri, 18 Apr 2025 18:54:32 +0200
From: Pavel Machek <pavel@...x.de>
To: Sasha Levin <sashal@...nel.org>
Cc: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Max Grobecker <max@...becker.info>, Ingo Molnar <mingo@...nel.org>,
	Borislav Petkov <bp@...en8.de>, tglx@...utronix.de,
	mingo@...hat.com, dave.hansen@...ux.intel.com, x86@...nel.org,
	thomas.lendacky@....com, perry.yuan@....com,
	mario.limonciello@....com, riel@...riel.com, mjguzik@...il.com,
	seanjc@...gle.com, darwi@...utronix.de
Subject: Re: [PATCH AUTOSEL 5.10 2/6] x86/cpu: Don't clear
 X86_FEATURE_LAHF_LM flag in init_amd_k8() on AMD when running in a virtual
 machine

Hi!

> From: Max Grobecker <max@...becker.info>
> 
> [ Upstream commit a4248ee16f411ac1ea7dfab228a6659b111e3d65 ]

> This can prevent some docker containers from starting or build scripts to create
> unoptimized binaries.
> 
> Admittably, this is more a small inconvenience than a severe bug in the kernel
> and the shoddy scripts that rely on parsing /proc/cpuinfo
> should be fixed instead.

I'd say this is not good stable candidate.

Best regards,
								Pavel

> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -839,7 +839,7 @@ static void init_amd_k8(struct cpuinfo_x86 *c)
>  	 * (model = 0x14) and later actually support it.
>  	 * (AMD Erratum #110, docId: 25759).
>  	 */
> -	if (c->x86_model < 0x14 && cpu_has(c, X86_FEATURE_LAHF_LM)) {
> +	if (c->x86_model < 0x14 && cpu_has(c, X86_FEATURE_LAHF_LM) && !cpu_has(c, X86_FEATURE_HYPERVISOR)) {
>  		clear_cpu_cap(c, X86_FEATURE_LAHF_LM);
>  		if (!rdmsrl_amd_safe(0xc001100d, &value)) {
>  			value &= ~BIT_64(32);

-- 
DENX Software Engineering GmbH,        Managing Director: Erika Unter
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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