From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH v4 5/6] KVM: MMU: combine guest pte read between walk and pte prefetch Date: Sat, 03 Jul 2010 15:44:45 +0300 Message-ID: <4C2F30BD.7050702@redhat.com> References: <4C2C9DC0.8050607@cn.fujitsu.com> <4C2C9E6C.2040803@cn.fujitsu.com> <20100702170303.GC25969@amt.cnet> <4C2F117C.2000006@cn.fujitsu.com> <4C2F2835.5060508@redhat.com> <4C2F2A0C.90704@cn.fujitsu.com> <4C2F2C5B.9020503@redhat.com> <4C2F2DBB.50904@cn.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , LKML , KVM list To: Xiao Guangrong Return-path: In-Reply-To: <4C2F2DBB.50904@cn.fujitsu.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 07/03/2010 03:31 PM, Xiao Guangrong wrote: > > Avi Kivity wrote: > > >>> >>> >> if (!direct) { >> r = kvm_read_guest_atomic(vcpu->kvm, >> gw->pte_gpa[level - 2], >> &curr_pte, sizeof(curr_pte)); >> if (r || curr_pte != gw->ptes[level - 2]) { >> kvm_mmu_put_page(shadow_page, sptep); >> kvm_release_pfn_clean(pfn); >> sptep = NULL; >> break; >> } >> } >> >> the code you moved... under what scenario is it not sufficient? >> >> > I not move those code, just use common function instead, that it's > FNAME(check_level_mapping)(), there are do the same work. > > And this check is not sufficient, since it's only checked if the > mapping is zapped or not exist, for other words only when broken this > judgment: > is_shadow_present_pte(*sptep)&& !is_large_pte(*sptep) > > but if the middle level is present and it's not the large mapping, > this check is skipped. > Well, in the description, it looked like everything was using small pages (in kvm, level=1 means PTE level, we need to change this one day). Please describe again and say exactly when the guest or host uses large pages. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.