linux-kernel - Re: [RFC PATCH 01/56] Documentation/admin-guide: Add documentation

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Message-ID: <yyzwkqzv2njelf3uhuy5x22hl7p3nvl6nilcakyjvxscccrpcm@zqnol2wanwey>
Date: Thu, 16 Oct 2025 14:24:53 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: David Kaplan <david.kaplan@....com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>, 
	Peter Zijlstra <peterz@...radead.org>, Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, 
	Ingo Molnar <mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H . Peter Anvin" <hpa@...or.com>, Alexander Graf <graf@...zon.com>, 
	Boris Ostrovsky <boris.ostrovsky@...cle.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 01/56] Documentation/admin-guide: Add documentation

On Mon, Oct 13, 2025 at 09:33:49AM -0500, David Kaplan wrote:
> +Runtime Limitations
> +^^^^^^^^^^^^^^^^^^^
> +
> +There are a few mitigations that cannot be toggled at runtime due to the way
> +they are structured.  Specifically, kernel PTI (page table isolation) cannot be
> +toggled because of the complexity of this mitigation.  Additionally, SMT cannot
> +be disabled at runtime.  Therefore, if a bug mitigation requires disabling SMT,
> +a warning message will be printed.

Is there a particular reason SMT can't be disabled?  There's definitely
a way to do it, see /sys/devices/system/cpu/smt/{active,control}.

-- 
Josh