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Message-ID: <1519033461.7876.58.camel@infradead.org>
Subject: Re: [tip:x86/pti] x86/speculation: Use IBRS if available before
 calling into firmware
From:   David Woodhouse <dwmw2@infradead.org>
To:     Ingo Molnar <mingo@kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Tim Chen <tim.c.chen@linux.intel.com>, hpa@zytor.com,
        tglx@linutronix.de, torvalds@linux-foundation.org,
        linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org,
        Borislav Petkov <bp@alien8.de>
In-Reply-To: <20180219093927.644jb6h5peworj62@gmail.com>
References: <1518362359-1005-1-git-send-email-dwmw@amazon.co.uk>
         <tip-670c3e8da87fa4046a55077b1409cf250865a203@git.kernel.org>
         <c77b3da9-136d-9988-119f-e94c86fd34a3@linux.intel.com>
         <1518808600.7876.49.camel@infradead.org>
         <66f94cb1-8160-56e0-680c-2e847ae05893@linux.intel.com>
         <20180217102616.vcwatxsgj2vunlew@gmail.com>
         <20180219092017.GN25201@hirez.programming.kicks-ass.net>
         <1519032552.7876.55.camel@infradead.org>
         <20180219093927.644jb6h5peworj62@gmail.com>
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Date:   Mon, 19 Feb 2018 09:44:21 +0000
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On Mon, 2018-02-19 at 10:39 +0100, Ingo Molnar wrote:
> * David Woodhouse <dwmw2@infradead.org> wrote:
>=20
> >=20
> > On Mon, 2018-02-19 at 10:20 +0100, Peter Zijlstra wrote:
> > >=20
> > >=20
> > > I did not update or otherwise change packages while I was bisecting; =
the
> > > machine is:
> > >=20
> > > vendor_id=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 : GenuineIntel
> > > cpu family=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 : 6
> > > model=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 : 6=
2
> > > model name=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 : Intel(R) Xeon(R) CPU E5-26=
80 v2 @ 2.80GHz
> > > stepping=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 : 4
> > > microcode=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 : 0x428
> > That's IVX with a microcode that doesn't *have* IBRS/IBPB. I don't
> > think there's a publicly available microcode that does; I assume you
> > didn't have one and build it into your kernel for early loading, and
> > thus you really weren't even using IBRS here? The code never even gets
> > patched in?
> Note that PeterZ's boot troubles only match the *symptoms* of the spuriou=
s=C2=A0
> failures reported by Tim Chen. Your commit wasn't bisected to.
>=20
> I linked these two reports on the (remote) possibility that they might be=
 related=C2=A0
> via some alignment dependent bug somewhere else in the x86 kernel - possi=
bly=C2=A0
> completely unrelated to any IBRS/IBPB details.

Understood. I was merely *accentuating* the "completely unrelated to
any IBRS/IBPB" bit, in a "la la la I'm ignoring this because I'm
working on other things" kind of a way... :)

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