linux-kernel - Re: [PATCH v3 06/35] x86/bugs: Restructure mmio mitigation

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Message-ID: <CA+i-1C2RnU0DOX0ryYMGZt8PXUD0BjBMpNDBHfX2HpDB0kBgCA@mail.gmail.com>
Date: Mon, 10 Feb 2025 17:42:20 +0100
From: Brendan Jackman <jackmanb@...gle.com>
To: David Kaplan <david.kaplan@....com>
Cc: 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>, 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 06/35] x86/bugs: Restructure mmio mitigation

On Wed, 8 Jan 2025 at 21:27, David Kaplan <david.kaplan@....com> wrote:
> +static void __init mmio_apply_mitigation(void)
> +{
>         if (mmio_mitigation == MMIO_MITIGATION_OFF)
>                 return;

> /*
> * Enable CPU buffer clear mitigation for host and VMM, if also affected
> * by MDS or TAA. Otherwise, enable mitigation for VMM only.
> */
> if (boot_cpu_has_bug(X86_BUG_MDS) || (boot_cpu_has_bug(X86_BUG_TAA) &&
>       boot_cpu_has(X86_FEATURE_RTM)))
> setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);

This is still peeking at other mitigations in _apply_mitigation.
Shouldn't we shunt that logic into _update_mitigation?

I guess this would need a new enum value but that doesn't seem too
bad. Worth it to have all the inter-mitigation dependencies localised
into *_udpate_mitigation IMO.