From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755298Ab0CQVP3 (ORCPT ); Wed, 17 Mar 2010 17:15:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:9122 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753562Ab0CQVP1 (ORCPT ); Wed, 17 Mar 2010 17:15:27 -0400 Message-ID: <4BA1464C.2020507@redhat.com> Date: Wed, 17 Mar 2010 11:14:52 -1000 From: Zachary Amsden User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.8) Gecko/20100301 Fedora/3.0.3-1.fc12 Thunderbird/3.0.3 MIME-Version: 1.0 To: Sheng Yang CC: Avi Kivity , "Zhang, Yanmin" , Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Marcelo Tosatti , oerg Roedel , Jes Sorensen , Gleb Natapov , "Huang, Zhiteng" , Joerg Roedel Subject: Re: [PATCH] Enhance perf to collect KVM guest os statistics from host side References: <1268717232.2813.36.camel@localhost> <4B9F5021.3080206@redhat.com> <1268793273.2813.70.camel@localhost> <201003171728.43739.sheng@linux.intel.com> In-Reply-To: <201003171728.43739.sheng@linux.intel.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/16/2010 11:28 PM, Sheng Yang wrote: > On Wednesday 17 March 2010 10:34:33 Zhang, Yanmin wrote: > >> On Tue, 2010-03-16 at 11:32 +0200, Avi Kivity wrote: >> >>> On 03/16/2010 09:48 AM, Zhang, Yanmin wrote: >>> >>>> Right, but there is a scope between kvm_guest_enter and really running >>>> in guest os, where a perf event might overflow. Anyway, the scope is >>>> very narrow, I will change it to use flag PF_VCPU. >>>> >>> There is also a window between setting the flag and calling 'int $2' >>> where an NMI might happen and be accounted incorrectly. >>> >>> Perhaps separate the 'int $2' into a direct call into perf and another >>> call for the rest of NMI handling. I don't see how it would work on svm >>> though - AFAICT the NMI is held whereas vmx swallows it. >>> >>> I guess NMIs >>> will be disabled until the next IRET so it isn't racy, just tricky. >>> >> I'm not sure if vmexit does break NMI context or not. Hardware NMI context >> isn't reentrant till a IRET. YangSheng would like to double check it. >> > After more check, I think VMX won't remained NMI block state for host. That's > means, if NMI happened and processor is in VMX non-root mode, it would only > result in VMExit, with a reason indicate that it's due to NMI happened, but no > more state change in the host. > > So in that meaning, there _is_ a window between VMExit and KVM handle the NMI. > Moreover, I think we _can't_ stop the re-entrance of NMI handling code because > "int $2" don't have effect to block following NMI. > > And if the NMI sequence is not important(I think so), then we need to generate > a real NMI in current vmexit-after code. Seems let APIC send a NMI IPI to > itself is a good idea. > > I am debugging a patch based on apic->send_IPI_self(NMI_VECTOR) to replace > "int $2". Something unexpected is happening... > You can't use the APIC to send vectors 0x00-0x1f, or at least, aren't supposed to be able to. Zach