From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756317Ab2K1WlC (ORCPT ); Wed, 28 Nov 2012 17:41:02 -0500 Received: from e23smtp05.au.ibm.com ([202.81.31.147]:39024 "EHLO e23smtp05.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755996Ab2K1WlA (ORCPT ); Wed, 28 Nov 2012 17:41:00 -0500 Message-ID: <50B692F3.4000408@linux.vnet.ibm.com> Date: Thu, 29 Nov 2012 06:40:51 +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: Gleb Natapov , 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> <50B626D7.7070608@linux.vnet.ibm.com> <20121128215750.GA10039@amt.cnet> In-Reply-To: <20121128215750.GA10039@amt.cnet> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit x-cbid: 12112822-1396-0000-0000-0000023A57A6 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/29/2012 05:57 AM, Marcelo Tosatti wrote: > On Wed, Nov 28, 2012 at 10:59:35PM +0800, Xiao Guangrong wrote: >> 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. :) > > I do object, since it is possible to detect precisely the condition by > storing which gfns have been cached. > > Then, Xiao, you need a way to handle large read-only sptes. Sorry, Marcelo, i am still confused why read-only sptes can not work under this patch? The code after read-only large spte is is: + if ((level > PT_PAGE_TABLE_LEVEL && + has_wrprotected_page(vcpu->kvm, gfn, level)) || + mmu_need_write_protect(vcpu, gfn, can_unsync)) { pgprintk("%s: found shadow page for %llx, marking ro\n", __func__, gfn); ret = 1; It return 1, then reexecute_instruction return 0. It is the same as without readonly large-spte.