linux-kernel - RE: [patch RFC 5/5] x86/speculation: Add basic speculation control code

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Date:   Wed, 10 Jan 2018 14:14:23 +0000
From:   "Van De Ven, Arjan" <arjan.van.de.ven@...el.com>
To:     Andrea Arcangeli <aarcange@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
CC:     David Woodhouse <dwmw2@...radead.org>,
        Jiri Kosina <jikos@...nel.org>,
        "Mallick, Asit K" <asit.k.mallick@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "Borislav Petkov" <bp@...en8.de>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: RE: [patch RFC 5/5] x86/speculation: Add basic speculation control
 code

> Hello,
> 
> On Wed, Jan 10, 2018 at 02:46:22PM +0100, Thomas Gleixner wrote:
> > So here is the simple list of questions all to be answered with YES or
> > NO. I don't want to see any of the 'but, though ...'. We all know by now
> > that it's CPU dependent and slow and whatever and that IBRS_ATT will be in
> > future CPUs. So get your act together and tell a clear YES or NO.
> 
> Other comments/code from Tim Chen, and Dave Hansen and most important
> the ibrs_enabled 2 description and implementation on lkml, makes me
> still wonder if even Arjan may have misunderstood some detail about
> IBRS semantics too.

I spent the better part of the last 6 months in dungeons with CPU designers trying to to figure out what we could and could not do. I'm pretty darn sure I know the details.