linux-kernel - RE: [PATCH v3 12/35] x86/bugs: Restructure retbleed mitigation

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Message-ID:
 <LV3PR12MB926577552148346FDB2CC83794F22@LV3PR12MB9265.namprd12.prod.outlook.com>
Date: Mon, 10 Feb 2025 20:50:57 +0000
From: "Kaplan, David" <David.Kaplan@....com>
To: Brendan Jackman <jackmanb@...gle.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" <x86@...nel.org>, "H . Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v3 12/35] x86/bugs: Restructure retbleed mitigation

[AMD Official Use Only - AMD Internal Distribution Only]

> -----Original Message-----
> From: Brendan Jackman <jackmanb@...gle.com>
> Sent: Monday, February 10, 2025 12:35 PM
> To: Kaplan, David <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 12/35] x86/bugs: Restructure retbleed mitigation
>
> Caution: This message originated from an External Source. Use proper caution
> when opening attachments, clicking links, or responding.
>
>
> On Wed, 8 Jan 2025 at 21:29, David Kaplan <david.kaplan@....com> wrote:
> > @@ -1827,16 +1821,6 @@ static void __init spectre_v2_select_mitigation(void)
> >                         break;
> >                 }
> >
> > -               if (IS_ENABLED(CONFIG_MITIGATION_IBRS_ENTRY) &&
> > -                   boot_cpu_has_bug(X86_BUG_RETBLEED) &&
> > -                   retbleed_cmd != RETBLEED_CMD_OFF &&
> > -                   retbleed_cmd != RETBLEED_CMD_STUFF &&
> > -                   boot_cpu_has(X86_FEATURE_IBRS) &&
> > -                   boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) {
> > -                       mode = SPECTRE_V2_IBRS;
> > -                       break;
> > -               }
> > -
> >                 mode = spectre_v2_select_retpoline();
> >                 break;
>
> It isn't quite clear why this gets removed here. Doesn't
> retbleed_update_mitigation() still depend on this?
>
> It gets added back in 15/35 so this would be at most a problem of git history.

Thanks, I'll fix this.  The logic had to change because retbleed_cmd is removed as part of the restructure, but that doesn't mean the whole block needs to be removed...and it does move into spectre_v2_update_mitigation() in patch 15.

--David Kaplan