From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jes Sorensen Subject: Re: [PATCH] Write to read-only msr MSR_IA32_PERF_STATUS is harmless, ignore it! Date: Tue, 31 Aug 2010 18:33:34 +0200 Message-ID: <4C7D2EDE.7020708@redhat.com> References: <1283257029-24102-1-git-send-email-Jes.Sorensen@redhat.com> <4C7D2DA6.40105@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org To: Avi Kivity Return-path: Received: from mx1.redhat.com ([209.132.183.28]:57839 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753717Ab0HaQon (ORCPT ); Tue, 31 Aug 2010 12:44:43 -0400 Received: from int-mx03.intmail.prod.int.phx2.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.16]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id o7VGifaU000407 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Tue, 31 Aug 2010 12:44:42 -0400 In-Reply-To: <4C7D2DA6.40105@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 08/31/10 18:28, Avi Kivity wrote: > On 08/31/2010 03:17 PM, Jes.Sorensen@redhat.com wrote: >> From: Jes Sorensen >> >> We regularly see bug reports over this one, however it is a write to >> a read-only register which some operating systems (including Linux) >> tend to write to once in a while. >> >> Ignore the writes since they do no harm. >> > > Does Linux write it with wrmsr_safe()? If not, I don't see how it > works. If it does, then we shouldn't ignore the write, instead issue > the #GP as usual, but be silent about it. To be honest, I am having a hard time determining where the write happens. I looked at this with Gleb and the rip obtained by kvm_read_rip(vcpu) in the code doesn't indicate anything that resembles a wrmsr(). It was either a 560 outb(0xfe, 0x64); /* pulse reset low */ or 49 asm volatile("sti; hlt": : :"memory"); which makes no sense to me, but given it's x86, I am not sure if it could have come from the BIOS or something during reboot? Jes