linux-kernel - Re: [PATCH v2 4/8] x86/spec_ctrl: Add sysctl knobs to enable/disable SPEC

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Message-ID: <1515440039.7317.41.camel@amazon.co.uk>
Date:   Mon, 8 Jan 2018 19:34:00 +0000
From:   "Woodhouse, David" <dwmw@...zon.co.uk>
To:     Peter Zijlstra <peterz@...radead.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "hongjiu.lu@...el.com" <hongjiu.lu@...el.com>
CC:     Dave Hansen <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Andrea Arcangeli" <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        "Arjan Van De Ven" <arjan.van.de.ven@...el.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/8] x86/spec_ctrl: Add sysctl knobs to
 enable/disable SPEC_CTRL feature

On Mon, 2018-01-08 at 18:42 +0100, Peter Zijlstra wrote:
> On Mon, Jan 08, 2018 at 09:28:12AM -0800, Tim Chen wrote:
> > On 01/08/2018 08:14 AM, Peter Zijlstra wrote:
> > > On Mon, Jan 08, 2018 at 01:47:07PM +0100, Peter Zijlstra wrote:
> > >>> a good suggestion, but we encountered some issues with it either
> > >>> crashing the kernel at boot or not properly turning on/off.
> > > 
> > > The below boots, but I lack stuff to test the enabling.
> > 
> > Peter,
> > 
> > Thanks.  Will give it a spin.  One other concern is if
> > JUMP_LABEL is not configured, this may not work, and
> > we may still need fall back to a control variable.
> 
> Urgh yes.. I always forget about that case. Will the retpoline crud be
> backported to a GCC old enough to not have asm-goto? If not, we could
> make all of this simply require asm-goto.

I think HJ said he was planning to backport as far as 4.9. When was
asm-goto added?
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