From mboxrd@z Thu Jan  1 00:00:00 1970
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1753323AbeAFVXp (ORCPT <rfc822;ralf@linux-mips.org> + 1 other);
        Sat, 6 Jan 2018 16:23:45 -0500
Received: from Galois.linutronix.de ([146.0.238.70]:46791 "EHLO
        Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751399AbeAFVXo (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Sat, 6 Jan 2018 16:23:44 -0500
Date: Sat, 6 Jan 2018 22:23:38 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Andrew Cooper <andrew.cooper3@citrix.com>
cc: David Woodhouse <dwmw@amazon.co.uk>,
        Andi Kleen <ak@linux.intel.com>, Paul Turner <pjt@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linux-foundation.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Kees Cook <keescook@google.com>,
        Rik van Riel <riel@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Jiri Kosina <jikos@kernel.org>, gnomes@lxorguk.ukuu.org.uk,
        Thomas Lendacky <Thomas.Lendacky@amd.com>
Subject: Re: [PATCH v5 02/12] x86/retpoline: Add initial retpoline support
In-Reply-To: <0c150bb9-f5eb-2bf2-1f64-84c1b315868b@citrix.com>
Message-ID: <alpine.DEB.2.20.1801062222430.2376@nanos>
References: <1515239374-23361-1-git-send-email-dwmw@amazon.co.uk> <1515239374-23361-3-git-send-email-dwmw@amazon.co.uk> <0c150bb9-f5eb-2bf2-1f64-84c1b315868b@citrix.com>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version: 1.0
Content-Type: multipart/mixed; BOUNDARY="8323329-1323891241-1515273819=:2376"
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>

  This message is in MIME format.  The first part should be readable text,
  while the remaining parts are likely unreadable without MIME-aware tools.

--8323329-1323891241-1515273819=:2376
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8BIT

On Sat, 6 Jan 2018, Andrew Cooper wrote:
> On 06/01/18 11:49, David Woodhouse wrote:
> > diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> > index 372ba3f..40e6e54 100644
> > --- a/arch/x86/kernel/cpu/common.c
> > +++ b/arch/x86/kernel/cpu/common.c
> > @@ -904,6 +904,11 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
> >  
> >  	setup_force_cpu_bug(X86_BUG_SPECTRE_V1);
> >  	setup_force_cpu_bug(X86_BUG_SPECTRE_V2);
> > +#ifdef CONFIG_RETPOLINE
> > +	setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
> > +	if (c->x86_vendor == X86_VENDOR_AMD)
> > +		setup_force_cpu_cap(X86_FEATURE_RETPOLINE_AMD);
> 
> This isn't safe.  It needs to be dependant on finding that LFENCEs are
> actually dispatch serialising.
> 
> In particular, when virtualised, you'll most likely be saddled with the
> hypervisors choice of setting, in which case you need to use retpoline
> as a fallback.

On bare metal we are sure, the virtualization part is a different question.

Thanks,

	tglx
--8323329-1323891241-1515273819=:2376--