linux-kernel - Re: [PATCH v2] x86/its: use Sapphire Rapids+ feature to opt out

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Message-ID: <9cf0e05b-00e6-4954-96d5-fafeb6e6397a@intel.com>
Date: Thu, 16 Oct 2025 21:12:46 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Jon Kohler <jon@...anix.com>, Thomas Gleixner <tglx@...utronix.de>,
 Borislav Petkov <bp@...en8.de>, Peter Zijlstra <peterz@...radead.org>,
 Josh Poimboeuf <jpoimboe@...nel.org>,
 Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
 Jonathan Corbet <corbet@....net>, Ingo Molnar <mingo@...hat.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
 "H. Peter Anvin" <hpa@...or.com>, Brian Gerst <brgerst@...il.com>,
 Brendan Jackman <jackmanb@...gle.com>, "Ahmed S. Darwish"
 <darwi@...utronix.de>, Alexandre Chartre <alexandre.chartre@...cle.com>,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86/its: use Sapphire Rapids+ feature to opt out

On 10/16/25 18:18, Jon Kohler wrote:
> +	 * hardware, except in the situation where the guest is presented
> +	 * with a feature that only exists in non-vulnerable hardware.
>  	 */
> -	if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
> +	if (boot_cpu_has(X86_FEATURE_HYPERVISOR) &&
> +	    !boot_cpu_has(X86_FEATURE_BUS_LOCK_DETECT))
>  		return true;

This seems like a hack in its purest form. Even worse, it's an
_uncommented_ hack.

This is _literally_ what ITS_NO is for.

So it's a pretty strong NAK from me on this one. No thanks. If you think
this is useful, it's a great thing to carry in a local kernel fork, but
it has no place in mainline.