linux-kernel - Re: [PATCH v3 23/35] x86/bugs: Add attack vector controls for taa

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Message-ID: <20250211190102.eociwspojygpucrk@jpoimboe>
Date: Tue, 11 Feb 2025 11:01:02 -0800
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>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 23/35] x86/bugs: Add attack vector controls for taa

On Wed, Jan 08, 2025 at 02:25:03PM -0600, David Kaplan wrote:
> @@ -620,7 +624,8 @@ static void __init taa_apply_mitigation(void)
>  		 */
>  		setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
>  
> -		if (taa_nosmt || cpu_mitigations_auto_nosmt())
> +		if (taa_nosmt || cpu_mitigations_auto_nosmt() ||
> +		    cpu_mitigate_attack_vector(CPU_MITIGATE_CROSS_THREAD))
>  			cpu_smt_disable(false);

There's a huge overlap between cpu_mitigations_auto_nosmt() and
CPU_MITIGATE_CROSS_THREAD.

IIUC, the main difference is that cpu_mitigations_auto_nosmt() selects
all the vectors whereas mitigate_cross_thread=on can be combined with
individual vectors.

Maybe we need a should_disable_smt() helper which checks both?

-- 
Josh