RE: tip/master falls off NOP cliff with KPTI under KVM

[Dexuan Cui]

> From: David Woodhouse [mailto:dwmw2@xxxxxxxxxxxxx]
> Sent: Wednesday, January 24, 2018 23:53
> 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@xxxxxxxxxxxx> wrote:
> > >
> > > On Thu, 2018-01-11 at 01:34 +0300, Alexey Dobriyan wrote:
> > > >
> > > >
> > > > Bisection points to
> > > >
> > > > ÂÂÂÂÂÂÂÂf3433c1010c6af61c9897f0f0447f81b991feac1 is the first bad
> commit
> > > > ÂÂÂÂÂÂÂÂcommit f3433c1010c6af61c9897f0f0447f81b991feac1
> > > > ÂÂÂÂÂÂÂÂAuthor: David Woodhouse <dwmw@xxxxxxxxxxxx>
> > > > ÂÂÂÂÂÂÂÂDate:ÂÂÂTue Jan 9 14:43:11 2018 +0000
> > > >
> > > > ÂÂÂÂÂÂÂÂÂÂÂÂx86/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 save
> > Âme 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.

Thanks for the clarification, David!
I'm going to pull the latest version from Linus's master branch.

Thanks,
-- Dexuan