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Message-ID: <1516866801.30244.3.camel@infradead.org>
Subject: Re: tip/master falls off NOP cliff with KPTI under KVM
From:   David Woodhouse <dwmw2@infradead.org>
To:     Dexuan-Linux Cui <dexuan.linux@gmail.com>
Cc:     Alexey Dobriyan <adobriyan@gmail.com>, pbonzini@redhat.com,
        rkrcmar@redhat.com, tglx@linutronix.de, mingo@redhat.com,
        hpa@zytor.com, dave.hansen@linux.intel.com,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org, x86@kernel.org,
        arjan@linux.intel.com, decui@microsoft.com
In-Reply-To: <CAA42JLZe+_dCcbam-_KE-kGYCHbZ2OCyJTHV02yznwrdJVJ2hg@mail.gmail.com>
References: <20180110220814.GA29262@avx2> <20180110223457.GA1762@avx2>
         <1515624823.22302.260.camel@amazon.co.uk>
         <CAA42JLZe+_dCcbam-_KE-kGYCHbZ2OCyJTHV02yznwrdJVJ2hg@mail.gmail.com>
Face:   iVBORw0KGgoAAAANSUhEUgAAADAAAAAwBAMAAAClLOS0AAAAG1BMVEUHBwcUFBQpKSlGRkZhYWF9fX2Xl5eysrLMzMxFF+rXAAACaElEQVQ4y21UQXbbIBQE9wJALmAg6ToWON22FrhZthHgbvssUPathC7QWMful2JHSmtWwGg+zPxBCE0DU4QoJQgRgsg4w2gJjBNE8PjFBZgnQMBs+uZ1NQNQjZO3BV4AGDFC0f+l4DBG0VUAM4yv7SO8IgRdHXQ+A78HKL5OAeCfNQV5cHX8DsBUyIJKtYbt98BKaGNCKjfgFVkqYVLbkHKsRsbSCSa0T6npIqLrpRBgQKHUpQmgs9eEKaiUcooE8WWfCGVnBiUcn1uF2XhbfmN9apKnmMP2K4kizKkQWxuaVNOpU2cACIyxO1Po8ETHcXEDMVnozcejkAYA9iaD4pU0ZvNQ8VurNnTuFAYVtuIPUZW25PjDIjQAlGyffIiRQxoWAZBmJ0LTdW2Nyc0iP3DqRhxizvGJkBWZmyFVyZkddWzmBoIBVMpCCJ1CFzl98xav4VJKSSD45KbUT75ixikTphDSRh8+Uz7JLgUTAgAFwzqzjxc/nDY7WUApqY0OMdTwCKZSXplSKkgIRCHElCp8ZnhnKqXuwcNbk1L0VXE+I9alUXoHlLHl3mv7/dWQlJwtjREC7mu9L/U2jQyMUuO2EDS4q9Kl2ddm232bxIE5pjJuVwiljNn/Cfv25/T0cu5cZbwHGVq7h/zp0B4n3S99V/utD+Uo8BiGx9xCsOAV5z7/tjo4Z4z1Lvb90KZ7eFOoOeXOukqF2seo234YYuaQPpRP+cVZU5adT1Edun5Iz3z8fTz3+eSDh0Ip1c7zx1MaijGzTd/3MbRuBHz8cvcVgCMBRpOHvgu59WDhoat+nIZm+LWm9C/aaaGq5DCP9QAAAABJRU5ErkJggg==
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Date:   Thu, 25 Jan 2018 07:53:21 +0000
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On Wed, 2018-01-24 at 16:53 -0800, Dexuan-Linux Cui wrote:
> On Wed, Jan 10, 2018 at 2:53 PM, Woodhouse, David <dwmw@amazon.co.uk> wro=
te:
> >=20
> > On Thu, 2018-01-11 at 01:34 +0300, Alexey Dobriyan wrote:
> > >=20
> > >=20
> > > Bisection points to
> > >=20
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0f3433c1010c6af61c9897=
f0f0447f81b991feac1 is the first bad commit
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0commit f3433c1010c6af=
61c9897f0f0447f81b991feac1
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0Author: David Woodhou=
se <dwmw@amazon.co.uk>
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0Date:=C2=A0=C2=A0=C2=
=A0Tue Jan 9 14:43:11 2018 +0000
> > >=20
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0x86/retpoline/entry: Convert entry assembler indirect jumps
> > Thanks. We've fixed the underlying problem with the alternatives
> > mechanism, *and* changed the retpoline code not to actually rely on
> > said fix.
> Hi David and all,
> It looks the latest upstream tree did fix the issue.
> Can you please specify the related commit(s) that fixed the issue?
> I need to cherry-pick the fix. I suppose a quick reply from you would sav=
e
> =C2=A0me a lot of time. :-)

Hi Dexuan,

The above commit didn't ever make it into Linus' tree in that form; the
issues were fixed beforehand. So there isn't a subsequent commit that
fixes it. I think it might have just been removing some .align 16 from
nospec-branch.h?

The correct version has been backported to 4.9 and 4.4 releases
already; if you pulled in an early version directly from tip/x86/pti
then I'd recommend you drop it and pull in the real version instead.

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