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Date: Thu, 25 Jan 2018 15:58:35 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: David Woodhouse <dwmw2@infradead.org>
cc: arjan@linux.intel.com, karahmed@amazon.de, x86@kernel.org,
    linux-kernel@vger.kernel.org, tim.c.chen@linux.intel.com, bp@alien8.de,
    peterz@infradead.org, pbonzini@redhat.com, ak@linux.intel.com,
    torvalds@linux-foundation.org, gregkh@linux-foundation.org,
    dave.hansen@intel.com, gnomes@lxorguk.ukuu.org.uk, ashok.raj@intel.com,
    mingo@kernel.org
Subject: Re: [PATCH v4 6/7] x86/cpufeature: Blacklist SPEC_CTRL on early
 Spectre v2 microcodes
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On Thu, 25 Jan 2018, David Woodhouse 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.

Thanks for that. That's the only sensible approach as long as we have to
deal with the current Quality Assumptions...

Thanks,

	tglx