linux-kernel - RE: [PATCH v4 04/36] x86/bugs: Restructure rfds mitigation

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Message-ID:
 <LV3PR12MB92656DCE365B8F955AB1072A94B32@LV3PR12MB9265.namprd12.prod.outlook.com>
Date: Mon, 14 Apr 2025 19:10:46 +0000
From: "Kaplan, David" <David.Kaplan@....com>
To: Josh Poimboeuf <jpoimboe@...nel.org>
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" <x86@...nel.org>, "H .
 Peter Anvin" <hpa@...or.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, Brendan Jackman <jackmanb@...gle.com>, Derek
 Manwaring <derekmn@...zon.com>
Subject: RE: [PATCH v4 04/36] x86/bugs: Restructure rfds mitigation

[AMD Official Use Only - AMD Internal Distribution Only]

> -----Original Message-----
> From: Josh Poimboeuf <jpoimboe@...nel.org>
> Sent: Thursday, April 10, 2025 11:25 AM
> To: Kaplan, David <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; Brendan Jackman
> <jackmanb@...gle.com>; Derek Manwaring <derekmn@...zon.com>
> Subject: Re: [PATCH v4 04/36] x86/bugs: Restructure rfds mitigation
>
> Caution: This message originated from an External Source. Use proper caution
> when opening attachments, clicking links, or responding.
>
>
> On Mon, Mar 10, 2025 at 11:39:51AM -0500, David Kaplan wrote:
> >  static void __init rfds_select_mitigation(void)  {
> >       if (!boot_cpu_has_bug(X86_BUG_RFDS) || cpu_mitigations_off()) {
> >               rfds_mitigation = RFDS_MITIGATION_OFF;
> >               return;
> >       }
> > -     if (rfds_mitigation == RFDS_MITIGATION_OFF)
> > -             return;
>
> The removal of this RFDS_MITIGATION_OFF check can cause
> verw_mitigation_selected to get wrongly enabled below if it was
> RFDS_MITIGATION_OFF to begin with.
>
> I think it's only a bisection issue, that gets re-added later with
> "x86/bugs: Add attack vector controls for rfds".
>

Ah, good catch.  Will fix.

Thanks --David Kaplan