linux-kernel - Re: [PATCH v4 2/5] cpu/speculation: Fix CPU mitigation defaults for !x86

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Date: Tue, 23 Apr 2024 07:10:23 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Josh Poimboeuf <jpoimboe@...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>, 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>, 
	Ingo Molnar <mingo@...nel.org>, Stephen Rothwell <sfr@...b.auug.org.au>, 
	Michael Ellerman <mpe@...erman.id.au>, Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH v4 2/5] cpu/speculation: Fix CPU mitigation defaults for !x86

On Fri, Apr 19, 2024, Sean Christopherson wrote:
> On Fri, Apr 19, 2024, Josh Poimboeuf wrote:
> > CPU speculative execution mitigations were inadvertently disabled on
> > non-x86 arches by the following commit:
> > 
> >  f337a6a21e2f ("x86/cpu: Actually turn off mitigations by default for SPECULATION_MITIGATIONS=n")
> > 
> > Fix it by replacing CONFIG_SPECULATION_MITIGATIONS with a new generic
> > CONFIG_CPU_MITIGATIONS option and moving the x86-specific mitigations to
> > a separate menu which depends on CONFIG_CPU_MITIGATIONS.
> 
> Ah drat, I didn't check my mailbox until after Cc'ing Linus my own version[*].
> 
> I don't have a strong preference between the two, though I do think it's worth
> nothing that this will (obvioulsy) allow disabling mitigations at compile time
> on all architectures, which may or may not be desirable.
> 
> [*] https://lore.kernel.org/all/20240420000556.2645001-2-seanjc@google.com

Josh, when you get a chance, can you weigh in on my menu-preserving approach?

I want to get this resolved asap so that we're not scrambing on Friday again :-)