linux-kernel - Re: [RFC PATCH 21/34] x86/bugs: Add attack vector controls for mds

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Message-ID: <2957b59e-25f4-4510-9053-8ad5067a60e5@amazon.com>
Date: Mon, 30 Sep 2024 17:50:12 -0700
From: "Manwaring, Derek" <derekmn@...zon.com>
To: <david.kaplan@....com>
CC: <bp@...en8.de>, <dave.hansen@...ux.intel.com>, <hpa@...or.com>,
	<jpoimboe@...nel.org>, <linux-kernel@...r.kernel.org>, <mingo@...hat.com>,
	<pawan.kumar.gupta@...ux.intel.com>, <peterz@...radead.org>,
	<tglx@...utronix.de>, <x86@...nel.org>
Subject: Re: [RFC PATCH 21/34] x86/bugs: Add attack vector controls for mds

On 2024-09-12 14:08-0500 David Kaplan wrote:
> @@ -446,7 +450,8 @@ static void __init mds_apply_mitigation(void)
>      if (mds_mitigation == MDS_MITIGATION_FULL) {
>          setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
>          if (!boot_cpu_has(X86_BUG_MSBDS_ONLY) &&
> -            (mds_nosmt || cpu_mitigations_auto_nosmt()))
> +            (mds_nosmt || cpu_mitigations_auto_nosmt() ||
> +             cpu_mitigate_attack_vector(CPU_MITIGATE_CROSS_THREAD)))
>              cpu_smt_disable(false);
>      }
>  }

Maybe I'm missing something here - if you care about user/user, why
would you not care about cross-thread? It seems to me SMT should be
turned off for all of the vectors.

Derek