From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754910Ab3EVIqX (ORCPT ); Wed, 22 May 2013 04:46:23 -0400 Received: from e23smtp06.au.ibm.com ([202.81.31.148]:50474 "EHLO e23smtp06.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754646Ab3EVIqR (ORCPT ); Wed, 22 May 2013 04:46:17 -0400 Message-ID: <519C85CC.6040103@linux.vnet.ibm.com> Date: Wed, 22 May 2013 16:46:04 +0800 From: Xiao Guangrong User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 MIME-Version: 1.0 To: Gleb Natapov CC: Marcelo Tosatti , avi.kivity@gmail.com, pbonzini@redhat.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH v6 3/7] KVM: MMU: fast invalidate all pages References: <1368738782-18649-1-git-send-email-xiaoguangrong@linux.vnet.ibm.com> <1368738782-18649-4-git-send-email-xiaoguangrong@linux.vnet.ibm.com> <20130520194624.GA21392@amt.cnet> <20130520201545.GC14287@redhat.com> <20130520204047.GA23364@amt.cnet> <20130521083902.GW4725@redhat.com> <20130522013330.GA8583@amt.cnet> <20130522063413.GL14287@redhat.com> In-Reply-To: <20130522063413.GL14287@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13052208-7014-0000-0000-0000030EC183 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/22/2013 02:34 PM, Gleb Natapov wrote: > On Tue, May 21, 2013 at 10:33:30PM -0300, Marcelo Tosatti wrote: >> On Tue, May 21, 2013 at 11:39:03AM +0300, Gleb Natapov wrote: >>>> Any pages with stale information will be zapped by kvm_mmu_zap_all(). >>>> When that happens, page faults will take place which will automatically >>>> use the new generation number. >>>> >>>> So still not clear why is this necessary. >>>> >>> This is not, strictly speaking, necessary, but it is the sane thing to do. >>> You cannot update page's generation number to prevent it from been >>> destroyed since after kvm_mmu_zap_all() completes stale ptes in the >>> shadow page may point to now deleted memslot. So why build shadow page >>> table with a page that is in a process of been destroyed? >> >> OK, can this be introduced separately, in a later patch, with separate >> justification, then? >> >> Xiao please have the first patches of the patchset focus on the problem >> at hand: fix long mmu_lock hold times. >> >>> Not sure what you mean again. We flush TLB once before entering this function. >>> kvm_reload_remote_mmus() does this for us, no? >> >> kvm_reload_remote_mmus() is used as an optimization, its separate from the >> problem solution. >> >>>> >>>> What was suggested was... go to phrase which starts with "The only purpose >>>> of the generation number should be to". >>>> >>>> The comment quoted here does not match that description. >>>> >>> The comment describes what code does and in this it is correct. >>> >>> You propose to not reload roots right away and do it only when root sp >>> is encountered, right? So my question is what's the point? There are, >>> obviously, root sps with invalid generation number at this point, so >>> reload will happen regardless in kvm_mmu_prepare_zap_page(). So why not >>> do it here right away and avoid it in kvm_mmu_prepare_zap_page() for >>> invalid and obsolete sps as I proposed in one of my email? >> >> Sure. But Xiao please introduce that TLB collapsing optimization as a >> later patch, so we can reason about it in a more organized fashion. > > So, if I understand correctly, you are asking to move is_obsolete_sp() > check from kvm_mmu_get_page() and kvm_reload_remote_mmus() from > kvm_mmu_invalidate_all_pages() to a separate patch. Fine by me, but if > we drop kvm_reload_remote_mmus() from kvm_mmu_invalidate_all_pages() the > call to kvm_mmu_invalidate_all_pages() in emulator_fix_hypercall() will > become nop. But I question the need to zap all shadow pages tables there > in the first place, why kvm_flush_remote_tlbs() is not enough? I do not know too... I even do no know why kvm_flush_remote_tlbs is needed. :(