Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752641AbeAFTra (ORCPT <rfc822;ralf@linux-mips.org> + 1 other);
        Sat, 6 Jan 2018 14:47:30 -0500
Received: from Galois.linutronix.de ([146.0.238.70]:46680 "EHLO
        Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751509AbeAFTr3 (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Sat, 6 Jan 2018 14:47:29 -0500
Date: Sat, 6 Jan 2018 20:47:19 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Dave Hansen <dave.hansen@intel.com>
cc: "Van De Ven, Arjan" <arjan.van.de.ven@intel.com>,
        Konrad Rzeszutek Wilk <konrad@kernel.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andi Kleen <ak@linux.intel.com>,
        David Woodhouse <dwmw@amazon.co.uk>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 4/8] x86/spec_ctrl: Add sysctl knobs to enable/disable
 SPEC_CTRL feature
In-Reply-To: <fab71cca-1a06-d10b-5129-0188b2790a11@intel.com>
Message-ID: <alpine.DEB.2.20.1801062043530.2376@nanos>
References: <cover.1515204614.git.tim.c.chen@linux.intel.com> <b77c0cfc2d50ebdaa721f95012fd735cc374f04c.1515204614.git.tim.c.chen@linux.intel.com> <20180106144110.GA2592@localhost.localdomain> <742ed1d9-7210-8443-0373-5af74f193ab9@intel.com>
 <0575AF4FD06DD142AD198903C74E1CC87A56C6FE@ORSMSX103.amr.corp.intel.com> <fab71cca-1a06-d10b-5129-0188b2790a11@intel.com>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
X-Linutronix-Spam-Score: -1.0
X-Linutronix-Spam-Level: -
X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required,  ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Return-Path: <linux-kernel-owner@vger.kernel.org>

On Sat, 6 Jan 2018, Dave Hansen wrote:

> On 01/06/2018 09:41 AM, Van De Ven, Arjan wrote:
> >>>>  .macro DISABLE_IBRS
> >>>> -	ALTERNATIVE "jmp .Lskip_\@", "", X86_FEATURE_SPEC_CTRL
> >>>> +	testl	$1, dynamic_ibrs
> >>> On every system call we end up hammering on this 'dynamic_ibrs'
> >>> variable. And it looks like it can be flipped via the IPI mechanism.
> >>>
> >>> Would it make sense for this to be per-cpu?
> >>
> >> It's probably better to either just make it __read_mostly or get the
> >> static branches that folks were suggesting actually working.
> > 
> > I still wonder if this isn't just better as a boot command line
> 
> It's simpler that way.  But, ideally, we want to make it runtime
> switchable to match the implementation in the distros.

Stop this silly argument please. The distros shipped lots of crap which we
dont want to have at all.

I told you folks yesterday what I want to see and the sysctl thing is the
least on that list and it's not needed for getting the important thing -
the protection - to work.

Can we pretty please do the basics and worry about that sysctl or whatever
people have on their wishlist once the dust settled.

Thanks,

	tglx