From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765973AbZFOTDy (ORCPT ); Mon, 15 Jun 2009 15:03:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755960AbZFOTDq (ORCPT ); Mon, 15 Jun 2009 15:03:46 -0400 Received: from mx2.redhat.com ([66.187.237.31]:47430 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751672AbZFOTDp (ORCPT ); Mon, 15 Jun 2009 15:03:45 -0400 Message-ID: <4A369ADF.2050305@redhat.com> Date: Mon, 15 Jun 2009 22:02:55 +0300 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1b3pre) Gecko/20090513 Fedora/3.0-2.3.beta2.fc11 Lightning/1.0pre Thunderbird/3.0b2 MIME-Version: 1.0 To: "H. Peter Anvin" CC: Ingo Molnar , Mathieu Desnoyers , Linus Torvalds , mingo@redhat.com, paulus@samba.org, acme@redhat.com, linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl, penberg@cs.helsinki.fi, vegard.nossum@gmail.com, efault@gmx.de, jeremy@goop.org, npiggin@suse.de, tglx@linutronix.de, linux-tip-commits@vger.kernel.org Subject: Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods References: <20090615171845.GA7664@elte.hu> <20090615180527.GB4201@Krystal> <20090615182348.GC11248@elte.hu> <4A369573.1060504@zytor.com> <20090615184536.GH11248@elte.hu> <4A369914.4010903@zytor.com> In-Reply-To: <4A369914.4010903@zytor.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/15/2009 09:55 PM, H. Peter Anvin wrote: > Ingo Molnar wrote: > >>> I wouldn't actually expect that, *as long as* there is >>> serialization between the cr2 write and the cr2 read. >>> >> Well, is there any OS that heavily relies on cr2 writes and which >> uses them from NMI context, and which CPU makers care about? >> (Meaning: Windows, pretty much.) >> >> If not then i agree that in theory it should work fine, but in >> practice we only know that we dont know the unknown risk here ;-) >> >> > > I think you can drop "uses them from NMI context" from that statement; > writing to %cr2 is independent of the context. > > I can try to find out internally what Intel's position on writing %cr2 > is, but it'll take a while; however, KVM should be able to tell you if > any random OS uses %cr2 writes (as should a static disassembly of their > kernel.) > Linux is one such OS. When acting as a hypervisor it writes cr2 to present its guests with their expected environment (any hypervisor that uses virtualization extensions will of course need to do this). -- Do not meddle in the internals of kernels, for they are subtle and quick to panic.