From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755557Ab2K1O7q (ORCPT ); Wed, 28 Nov 2012 09:59:46 -0500 Received: from e28smtp03.in.ibm.com ([122.248.162.3]:37917 "EHLO e28smtp03.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755392Ab2K1O7p (ORCPT ); Wed, 28 Nov 2012 09:59:45 -0500 Message-ID: <50B626D7.7070608@linux.vnet.ibm.com> Date: Wed, 28 Nov 2012 22:59:35 +0800 From: Xiao Guangrong User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120911 Thunderbird/15.0.1 MIME-Version: 1.0 To: Gleb Natapov CC: Marcelo Tosatti , Avi Kivity , LKML , KVM Subject: Re: [PATCH 3/3] KVM: x86: improve reexecute_instruction References: <50AAC77C.8040505@linux.vnet.ibm.com> <50AAC7F9.7050305@linux.vnet.ibm.com> <20121126224105.GB10634@amt.cnet> <50B433D0.8060107@linux.vnet.ibm.com> <20121128141230.GI928@redhat.com> In-Reply-To: <20121128141230.GI928@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit x-cbid: 12112814-3864-0000-0000-000005C2595A Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/28/2012 10:12 PM, Gleb Natapov wrote: > On Tue, Nov 27, 2012 at 11:30:24AM +0800, Xiao Guangrong wrote: >> On 11/27/2012 06:41 AM, Marcelo Tosatti wrote: >> >>>> >>>> - return false; >>>> +again: >>>> + page_fault_count = ACCESS_ONCE(vcpu->kvm->arch.page_fault_count); >>>> + >>>> + /* >>>> + * if emulation was due to access to shadowed page table >>>> + * and it failed try to unshadow page and re-enter the >>>> + * guest to let CPU execute the instruction. >>>> + */ >>>> + kvm_mmu_unprotect_page(vcpu->kvm, gpa_to_gfn(gpa)); >>>> + emulate = vcpu->arch.mmu.page_fault(vcpu, cr3, PFERR_WRITE_MASK, false); >>> >>> Can you explain what is the objective here? >>> >> >> Sure. :) >> >> The instruction emulation is caused by fault access on cr3. After unprotect >> the target page, we call vcpu->arch.mmu.page_fault to fix the mapping of cr3. >> if it return 1, mmu can not fix the mapping, we should report the error, >> otherwise it is good to return to guest and let it re-execute the instruction >> again. >> >> page_fault_count is used to avoid the race on other vcpus, since after we >> unprotect the target page, other cpu can enter page fault path and let the >> page be write-protected again. >> >> This way can help us to detect all the case that mmu can not be fixed. >> > Can you write this in a comment above vcpu->arch.mmu.page_fault()? Okay, if Marcelo does not object this way. :)