Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752665Ab2BPQR2 (ORCPT ); Thu, 16 Feb 2012 11:17:28 -0500 Received: from mx1.redhat.com ([209.132.183.28]:18676 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752049Ab2BPQR0 (ORCPT ); Thu, 16 Feb 2012 11:17:26 -0500 Message-ID: <4F3D2C09.1020803@redhat.com> Date: Thu, 16 Feb 2012 18:17:13 +0200 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:9.0) Gecko/20111222 Thunderbird/9.0 MIME-Version: 1.0 To: Andy Lutomirski CC: Amit Shah , tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org, kvm list Subject: Re: [KVM paravirt issue?] Re: vsyscall=emulate regression References: <20120203082748.GB782@amit.redhat.com> <20120214122205.GA29418@amit.redhat.com> <20120215110122.GA3136@amit.redhat.com> In-Reply-To: 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 Content-Length: 2484 Lines: 66 On 02/15/2012 09:36 PM, Andy Lutomirski wrote: > Hi, kvm people- > > Here's a strange failure. It could be a bug in something > RHEL6-specific, but it could be a generic issue that only triggers > with a paravirt guest with old userspace on a non-ept host. There was > a bug like this on Xen, and I'm wondering something's wrong on kvm as > well. > > For background, a change in 3.1 (IIRC) means that, when > vsyscall=emulate or vsyscall=none, the vsyscall page in the fixmap is > NX. It seems like Amit's machine is marking the physical PTE present > but unreadable. No such thing as present and unreadable, without EPT. > So I could have messed up, or there could be a subtle > bug somewhere. Any ideas? What's the code trying to do? Execute an instruction from an non-executable page, trap the #PF, and emulate? And what are the symptoms? wrong error code for the #PF? That could easily be a kvm bug. > > I'll try to reproduce on a non-ept host later on, but that will > involve finding one. rmmod kvm-intel moprobe kvm-intel ept=0 > Hmm. You don't have ept. If your guest kernel supports paravirt, > then you might use the hypercall interface instead of programming the > fixmap directly. There is no hypercall interface for writing page tables in kvm. > > > > > This is what I get with vsyscall=none, where emulate and native work > > fine on the 3.2 kernel on different host hardware, the guest stays the > > same: > > > > > > [ 2.874661] debug: unmapping init memory ffffffff8167f000..ffffffff818dc000 > > [ 2.876778] Write protecting the kernel read-only data: 6144k > > [ 2.879111] debug: unmapping init memory ffff880001318000..ffff880001400000 > > [ 2.881242] debug: unmapping init memory ffff8800015a0000..ffff880001600000 > > [ 2.884637] init[1] vsyscall attempted with vsyscall=none ip:ffffffffff600400 cs:33 sp:7fff2f48fe18 ax:7fff2f48fe50 si:7fff2f48ff08 di:0 > > This like (vsyscall attempted) means that the emulation worked > correctly. Your other traces didn't have it or anything like it, > which mostly rules out do_emulate_vsyscall issues. > Can you point me at the code in question? Amit, a trace would be nice. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/