From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754812Ab3EVBmf (ORCPT ); Tue, 21 May 2013 21:42:35 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56062 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754734Ab3EVBmc (ORCPT ); Tue, 21 May 2013 21:42:32 -0400 Date: Tue, 21 May 2013 22:33:30 -0300 From: Marcelo Tosatti To: Gleb Natapov Cc: Xiao Guangrong , 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 Message-ID: <20130522013330.GA8583@amt.cnet> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130521083902.GW4725@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.