From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757362AbaCRSR4 (ORCPT ); Tue, 18 Mar 2014 14:17:56 -0400 Received: from mail.xen.prgmr.com ([71.19.149.6]:33438 "EHLO mail.xen.prgmr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756119AbaCRSRz (ORCPT ); Tue, 18 Mar 2014 14:17:55 -0400 Message-ID: <53288DD1.9060809@prgmr.com> Date: Tue, 18 Mar 2014 11:17:53 -0700 From: Sarah Newman User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.3.0 MIME-Version: 1.0 To: George Dunlap , Jan Beulich , "H. Peter Anvin" CC: Linux Kernel Mailing List , "xen-devel@lists.xen.org" , Ingo Molnar , David Vrabel , Thomas Gleixner Subject: Re: [Xen-devel] [PATCHv1] x86: don't schedule when handling #NM exception References: <1394468273-13676-1-git-send-email-david.vrabel@citrix.com> <531DEB11.2070709@zytor.com> <531DF319.6010800@citrix.com> <53266841.6090308@prgmr.com> <1ebfa80c-4a68-4602-bc98-e5d5f0893998@email.android.com> <5327291D.60009@zytor.com> <532739810200007800124E85@nat28.tlf.novell.com> <53272D79.5050605@eu.citrix.com> In-Reply-To: <53272D79.5050605@eu.citrix.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/17/2014 10:14 AM, George Dunlap wrote: > On 03/17/2014 05:05 PM, Jan Beulich wrote: >>>>> On 17.03.14 at 17:55, "H. Peter Anvin" wrote: >>> So if this interface wasn't an accident it was active negligence and >>> incompetence. >> I don't think so - while it (as we now see) disallows certain things >> inside the guest, back at the time when this was designed there was >> no sign of any sort of allocation/scheduling being done inside the >> #NM handler. And furthermore, a PV specification is by its nature >> allowed to define deviations from real hardware behavior, or else it >> wouldn't be needed in the first place. > > But it's certainly the case that deviating from the hardware in *this* way by default was always > very likely to case the exact kind of bug we've seen here. It is an "interface trap" that was bound > to be tripped over (much like Intel's infamous sysret vulnerability). > > Making it opt-in would have been a much better idea. But the people who made that decision are long > gone, and we now need to deal with the situation as we have it. Should or has there been a review of the current xen PVABI to look for any other such deviations?