linux-kernel - Re: [PATCH 7/7] x86/bugs: Replace CONFIG_SPECTRE_BHI_{ON,OFF} with CONFIG_MITIGATION_SPECTRE

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Message-ID: <20240411152459.53ofd6hmhfzgi6td@treble>
Date: Thu, 11 Apr 2024 08:24:59 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Ingo Molnar <mingo@...nel.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alexandre Chartre <alexandre.chartre@...cle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Sean Christopherson <seanjc@...gle.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	KP Singh <kpsingh@...nel.org>, Waiman Long <longman@...hat.com>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 7/7] x86/bugs: Replace CONFIG_SPECTRE_BHI_{ON,OFF} with
 CONFIG_MITIGATION_SPECTRE_BHI

On Thu, Apr 11, 2024 at 09:48:42AM +0200, Ingo Molnar wrote:
> > +++ b/arch/x86/kernel/cpu/bugs.c
> > @@ -1628,7 +1628,7 @@ enum bhi_mitigations {
> >  };
> >  
> >  static enum bhi_mitigations bhi_mitigation __ro_after_init =
> > -	IS_ENABLED(CONFIG_SPECTRE_BHI_ON) ? BHI_MITIGATION_ON : BHI_MITIGATION_OFF;
> > +	IS_ENABLED(CONFIG_MITIGATION_SPECTRE_BHI_ON) ? BHI_MITIGATION_ON : BHI_MITIGATION_OFF;
> 
> Uhm, after this patch there's no CONFIG_MITIGATION_SPECTRE_BHI_ON anymore, 
> which is kindof nasty, as IS_ENABLED() doesn't generate a build failure for 
> non-existent Kconfig variables IIRC ...
> 
> So AFAICT this patch turns on BHI unconditionally.
> 
> I've fixed as per the patch below, but please double check the end result 
> in tip:x86/urgent once I've pushed it out..

Oof, thanks.  The result in tip looks good.

We should add a permanent build time check to catch cases like this.

-- 
Josh