From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754210AbZFPIhH (ORCPT ); Tue, 16 Jun 2009 04:37:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753635AbZFPIgz (ORCPT ); Tue, 16 Jun 2009 04:36:55 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:58412 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751551AbZFPIgy (ORCPT ); Tue, 16 Jun 2009 04:36:54 -0400 Date: Tue, 16 Jun 2009 10:36:35 +0200 From: Ingo Molnar To: Avi Kivity Cc: "H. Peter Anvin" , 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 Message-ID: <20090616083635.GE16229@elte.hu> References: <20090615171845.GA7664@elte.hu> <20090615180527.GB4201@Krystal> <20090615182348.GC11248@elte.hu> <4A369573.1060504@zytor.com> <20090615184536.GH11248@elte.hu> <4A369914.4010903@zytor.com> <4A369ADF.2050305@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4A369ADF.2050305@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Avi Kivity wrote: > 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). Ah, it does save/restore it in svm_vcpu_run. VMX can do this via its context structure (without explicit CR manipulations in host space), right? Ingo