linux-kernel - Re: [RFC PATCH 11/56] x86/bugs: Reset MMIO mitigations

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Message-ID: <20260126130548.GHaXdmrPufeYlE_7Vk@fat_crate.local>
Date: Mon, 26 Jan 2026 14:05:48 +0100
From: Borislav Petkov <bp@...en8.de>
To: David Kaplan <david.kaplan@....com>
Cc: Thomas Gleixner <tglx@...utronix.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>, Alexander Graf <graf@...zon.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 11/56] x86/bugs: Reset MMIO mitigations

On Mon, Oct 13, 2025 at 09:33:59AM -0500, David Kaplan wrote:
> Add function to reset MMIO mitigations back to their boot-time defaults.
> 
> Signed-off-by: David Kaplan <david.kaplan@....com>
> ---
>  arch/x86/kernel/cpu/bugs.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index 5668a8b8821b..9139c8187913 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -787,6 +787,16 @@ static void __init mmio_apply_mitigation(void)
>  		cpu_smt_disable(false);
>  }
>  
> +#ifdef CONFIG_DYNAMIC_MITIGATIONS
> +static void mmio_reset_mitigation(void)
> +{
> +	static_branch_disable(&cpu_buf_vm_clear);

This needs to be

	setup_clear_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF_VM_MMIO);

I believe, after:

f6106d41ec84 ("x86/bugs: Use an x86 feature to track the MMIO Stale Data mitigation")

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette