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From: Ingo Molnar <mingo@kernel.org>
To: David Woodhouse <dwmw2@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	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
Subject: Re: [PATCH v4 6/7] x86/cpufeature: Blacklist SPEC_CTRL on early Spectre v2 microcodes
Date: Fri, 26 Jan 2018 10:40:37 +0100	[thread overview]
Message-ID: <20180126094036.uqi5w4qfvbuic37t@gmail.com> (raw)
In-Reply-To: <1516887714.30244.121.camel@infradead.org>


* David Woodhouse <dwmw2@infradead.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

  parent reply	other threads:[~2018-01-26  9:40 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-25  9:23 [PATCH v4 0/7] Basic Speculation Control feature support David Woodhouse
2018-01-25  9:23 ` [PATCH v4 1/7] x86/cpufeatures: Add CPUID_7_EDX CPUID leaf David Woodhouse
2018-01-25  9:23 ` [PATCH v4 2/7] x86/cpufeatures: Add Intel feature bits for Speculation Control David Woodhouse
2018-01-25  9:23 ` [PATCH v4 3/7] x86/cpufeatures: Add AMD " David Woodhouse
2018-01-25  9:23 ` [PATCH v4 4/7] x86/msr: Add definitions for new speculation control MSRs David Woodhouse
2018-01-25  9:23 ` [PATCH v4 5/7] x86/pti: Do not enable PTI on processors which are not vulnerable to Meltdown David Woodhouse
2018-01-25  9:42   ` Peter Zijlstra
2018-01-25  9:56     ` David Woodhouse
2018-01-25 10:01       ` Thomas Gleixner
2018-01-25 15:12   ` Alan Cox
2018-01-25  9:23 ` [PATCH v4 6/7] x86/cpufeature: Blacklist SPEC_CTRL on early Spectre v2 microcodes David Woodhouse
2018-01-25 10:43   ` David Woodhouse
2018-01-25 10:54     ` Thomas Gleixner
2018-01-25 11:20       ` David Woodhouse
2018-01-25 11:34         ` Thomas Gleixner
2018-01-25 13:41           ` David Woodhouse
2018-01-25 14:58             ` Thomas Gleixner
2018-01-25 16:16             ` Alan Cox
2018-01-25 16:24               ` Thomas Gleixner
2018-01-25 16:35                 ` David Woodhouse
2018-01-26  9:40             ` Ingo Molnar [this message]
2018-01-25  9:23 ` [PATCH v4 7/7] x86/speculation: Add basic IBPB (Indirect Branch Prediction Barrier) support David Woodhouse
2018-01-25 11:41   ` Borislav Petkov
2018-01-25 11:47     ` David Woodhouse
2018-01-25 11:50       ` Borislav Petkov
2018-01-25 11:58         ` David Woodhouse
2018-01-25 12:03           ` Borislav Petkov
2018-01-25 12:11             ` David Woodhouse

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