From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752160Ab0IWCyw (ORCPT ); Wed, 22 Sep 2010 22:54:52 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:60530 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751217Ab0IWCyu (ORCPT ); Wed, 22 Sep 2010 22:54:50 -0400 Message-ID: <4C9AC283.3000307@cn.fujitsu.com> Date: Thu, 23 Sep 2010 10:59:15 +0800 From: Xiao Guangrong User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.11) Gecko/20100713 Thunderbird/3.0.6 MIME-Version: 1.0 To: Avi Kivity CC: Marcelo Tosatti , LKML , KVM Subject: Re: [PATCH 4/4] KVM: MMU: Don't touch unsync sp in kvm_mmu_pte_write() References: <4C976D48.6020400@cn.fujitsu.com> <4C976DF6.1020905@cn.fujitsu.com> <4C977CBF.6030702@redhat.com> In-Reply-To: <4C977CBF.6030702@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/20/2010 11:24 PM, Avi Kivity wrote: > On 09/20/2010 04:21 PM, Xiao Guangrong wrote: >> Gfn may have many shadow pages, when one sp need be synced, we write >> protected sp->gfn and sync this sp but we keep other shadow pages >> asynchronous >> >> So, while gfn happen page fault, let it not touches unsync page, the >> unsync >> page only updated at invlpg/flush TLB time >> >> @@ -3157,6 +3164,9 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, >> gpa_t gpa, >> >> mask.cr0_wp = mask.cr4_pae = mask.nxe = 1; >> for_each_gfn_indirect_valid_sp(vcpu->kvm, sp, gfn, node) { >> + if (sp->unsync) >> + continue; >> + >> > > Not sure this is a win. If a gpte is updated from having p=0 to p=1 (or > permissions upgraded), we may not have an invlpg to sync the spte, since > the hardware doesn't require it. With this change, we may get an extra > #PF. > Avi, Thanks for your review, i think this case is not too bad since: 1: This case only impacts local vcpu since if permissions is increased, it's no need send IPT to flush remote vcpu's tlb, so even if we update unsync spte in kvm_mmu_pte_write() path, the #PF still occur on other vcpus. 2: If the unsync sp which is updated in kvm_mmu_pte_write() is not using by the vcpu, it will sync automatically after it's loaded. 3: If the sp is using, update this sp in kvm_mmu_pte_write() will avoid extra #PF, in this case, two(or more) sps have the same gfn, there are mapped in the same page table and with different kinds(unsync/sync), i thinks this case is infrequency. And even we updated it, we can not sure it can be accessed latter, So, i think it's better lazily update unsync sp until it's used or the flush time, your opinion? :-)