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Date: Wed, 10 Jan 2018 11:03:44 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: David Woodhouse <dwmw2@infradead.org>
Cc: Dave Hansen <dave.hansen@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        Borislav Petkov <bp@alien8.de>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andi Kleen <ak@linux.intel.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Arjan Van De Ven <arjan.van.de.ven@intel.com>
Subject: Re: [patch RFC 5/5] x86/speculation: Add basic speculation control
 code
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On Wed, Jan 10, 2018 at 09:27:59AM +0000, David Woodhouse wrote:
> > The only question I have is if retpoline works at all on SKL (with ucode
> > update); BDW needs the ucode update for retpoline to work because of the
> > RSB fallback.
> 
> As I understand it, Skylake is never getting the IBRS_ATT (all the
> time) feature. That is for future CPUs only.

Ah, so then I got confused by your earlier email. So retpoline will work
on SKL, but it will, like BDW need the ucode update?

> I don't know why you're calling that 'IBRS=2'; are you getting confused
> by Andrea's distro horridness?

Yes, continuation of the nomenclature of that earlier thread.

Still, point remains, do we ever need that MSR fiddling dynamic IBRS
stuff now that we have retpolines? I would prefer to not have it if
there is no compelling reason for it.