From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756625AbcECV2V (ORCPT ); Tue, 3 May 2016 17:28:21 -0400 Received: from mga09.intel.com ([134.134.136.24]:31055 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756527AbcECV2U (ORCPT ); Tue, 3 May 2016 17:28:20 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.24,574,1455004800"; d="scan'208";a="967997087" Subject: Re: [PATCH] [RFC] x86: work around MPX Erratum To: Borislav Petkov References: <20160502220341.9E8C34FC@viggo.jf.intel.com> <20160503064354.GA11112@gmail.com> <57291268.3060006@intel.com> <20160503211202.GA27604@pd.tnic> Cc: Ingo Molnar , linux-kernel@vger.kernel.org, x86@kernel.org, Andy Lutomirski , Thomas Gleixner , "H. Peter Anvin" , Linus Torvalds From: Dave Hansen Message-ID: <572917F2.2060302@intel.com> Date: Tue, 3 May 2016 14:28:18 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <20160503211202.GA27604@pd.tnic> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/03/2016 02:12 PM, Borislav Petkov wrote: > On Tue, May 03, 2016 at 02:04:40PM -0700, Dave Hansen wrote: >> My concern was not necessarily with folks booting with 'nosmep', but > > Btw, does anything speak for even keeping that 'nosmep' thing? Generally, I'm not sure we need the no$foo options at all. There's always "clearcpuid=" which does the same thing. It just requires you to go look up the X86_FEATURE_* bit first. >> with processors that have MPX present and SMEP fused off (or made >> unavailable by a hypervisor) and which are unaffected by this issue. > > So we won't init MPX on those... Yes, and as long as such a processor doesn't exist today and never exists in the future or the folks that buy such a processor truly don't care about MPX, that's fine to do. I'm just a bit nervous about the whole "never exists in the future" part. >> People would have to be very careful to never create a processor which >> did not have SMEP but did have MPX, since MPX would effectively be >> unusable on such a processor. > > We can disable that combination in qemu too, right? What do you mean by disable? Have qemu error out if MPX and SMEP aren't disabled in concert with each other?