linux-kernel - Re: [PATCH v4 6/7] x86/cpufeature: Blacklist SPEC

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Date:   Fri, 26 Jan 2018 10:40:37 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>, arjan@...ux.intel.com,
        karahmed@...zon.de, x86@...nel.org, linux-kernel@...r.kernel.org,
        tim.c.chen@...ux.intel.com, bp@...en8.de, peterz@...radead.org,
        pbonzini@...hat.com, ak@...ux.intel.com,
        torvalds@...ux-foundation.org, gregkh@...ux-foundation.org,
        dave.hansen@...el.com, gnomes@...rguk.ukuu.org.uk,
        ashok.raj@...el.com
Subject: Re: [PATCH v4 6/7] x86/cpufeature: Blacklist SPEC_CTRL on early
 Spectre v2 microcodes


* David Woodhouse <dwmw2@...radead.org> wrote:

> On Thu, 2018-01-25 at 12:34 +0100, Thomas Gleixner wrote:
> > 
> > This stuff is really a master piece of trainwreck engineering.
> > 
> > So yeah, whatever we do we end up with a proper mess. Lets go for a
> > blacklist and hope that we'll have something which holds at some
> > foreseeable day in the future.
> > 
> > The other concern I have is IBRS vs. IBPB. Are we sufficiently sure that
> > IBPB is working on those IBRS blacklisted ucode revisions? Or should we
> > just play safe and not touch any of this at all when we detect a
> > blacklisted one?
> 
> That isn't sufficiently clear to me. I've changed it back to blacklist
> *everything* for now, to be safe. If at any point Intel want to get
> their act together and give us coherent information to the contrary, we
> can change to separate IBPB/IBRS blacklists.

Yes.

I also agree that blacklists are the fundamentally correct approach here: a 
bit-rotting blacklist is far better to users than a bit-rotting whitelist, 
assuming that the number of CPU and microcode bugs goes down with time.

Thanks,

	Ingo