linux-kernel - RE: [PATCH v3 3/5] x86/enter: Use IBRS on syscall and interrupts

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Date:   Wed, 10 Jan 2018 18:47:08 +0000
From:   "Van De Ven, Arjan" <arjan.van.de.ven@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v3 3/5] x86/enter: Use IBRS on syscall and interrupts

> On SKL+ retpoline is mostly there, but has a few dinky holes in and it
> _might_ make sense to use IBRS.
> 
> But I feel it needs explaining what the exact holes are (pjt and dwmw2
> had a fair enumeration IIRC) such that people can judge the risk.

you are correct to need and want this.

the problem is one of patch sequencing a bit;

as retpoline is now it has more of these dinky holes, in the next few days
patches will flow that will fix a bunch of these.

I would like to suggest we do the documentation part after a few days once 
we know how much of these we can reasonable pre-plug.

but yes we must do this tradeoff documentation.