linux-kernel - RE: [PATCH 0/7] IBRS patch series

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Date:   Fri, 5 Jan 2018 16:44:17 +0000
From:   "Van De Ven, Arjan" <arjan.van.de.ven@...el.com>
To:     Andrea Arcangeli <aarcange@...hat.com>,
        David Woodhouse <dwmw2@...radead.org>
CC:     Paul Turner <pjt@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 0/7] IBRS patch series

> On Fri, Jan 05, 2018 at 04:37:30PM +0000, David Woodhouse wrote:
> > You are completely ignoring pre-Skylake here.
> >
> > On pre-Skylake, retpoline is perfectly sufficient and it's a *lot*
> > faster than the IBRS option which is almost prohibitively slow.
> >
> > We didn't do it just for fun. And it's working fine; it isn't *that*
> > complex.
> 
> How do you enable IBRS when the CPU switches to SMM?

you do not need to. SMM takes care of itself.