linux-kernel - Re: [PATCH v2 2/2] cpu: Ignore "mitigations" kernel parameter if CPU

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Date: Sat, 20 Apr 2024 15:36:30 +0200
From: Borislav Petkov <bp@...en8.de>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Michael Ellerman <mpe@...erman.id.au>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>, Will Deacon <will@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2 2/2] cpu: Ignore "mitigations" kernel parameter if
 CPU_MITIGATIONS=n

On Fri, Apr 19, 2024 at 05:05:55PM -0700, Sean Christopherson wrote:
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 619a04d5c131..928820e61cb5 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2495,9 +2495,13 @@ menuconfig CPU_MITIGATIONS
>  	help
>  	  Say Y here to enable options which enable mitigations for hardware
>  	  vulnerabilities (usually related to speculative execution).
> +	  Mitigations can be disabled or restricted to SMT systems at runtime
> +	  via the "mitigations" kernel parameter.
>  
> -	  If you say N, all mitigations will be disabled. You really
> -	  should know what you are doing to say so.
> +	  If you say N, all mitigations will be disabled.  This CANNOT be
> +	  overridden at runtime.

You probably wanna highlight the fact here that saying N means it'll
simply not even build in the mitigations code, leading to the physical
inability :) to enable them later, at run time.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette