From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933161Ab2K0Dae (ORCPT ); Mon, 26 Nov 2012 22:30:34 -0500 Received: from e23smtp07.au.ibm.com ([202.81.31.140]:35308 "EHLO e23smtp07.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933062Ab2K0Dac (ORCPT ); Mon, 26 Nov 2012 22:30:32 -0500 Message-ID: <50B433D0.8060107@linux.vnet.ibm.com> Date: Tue, 27 Nov 2012 11:30:24 +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: Marcelo Tosatti CC: 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> In-Reply-To: <20121126224105.GB10634@amt.cnet> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit x-cbid: 12112703-0260-0000-0000-00000237EC37 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.