From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933081AbcBYJzV (ORCPT ); Thu, 25 Feb 2016 04:55:21 -0500 Received: from mx1.redhat.com ([209.132.183.28]:47349 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933036AbcBYJzP (ORCPT ); Thu, 25 Feb 2016 04:55:15 -0500 Subject: Re: [PATCH 09/12] KVM: MMU: coalesce zapping page after mmu_sync_children To: Xiao Guangrong , Takuya Yoshikawa , linux-kernel@vger.kernel.org, kvm@vger.kernel.org References: <1456319873-34182-1-git-send-email-pbonzini@redhat.com> <1456319873-34182-10-git-send-email-pbonzini@redhat.com> <56CE63D1.40009@lab.ntt.co.jp> <56CEAEA7.8080702@linux.intel.com> <56CEC003.1070402@redhat.com> <56CEC516.7010306@linux.intel.com> Cc: mtosatti@redhat.com From: Paolo Bonzini X-Enigmail-Draft-Status: N1110 Message-ID: <56CECF7E.3050801@redhat.com> Date: Thu, 25 Feb 2016 10:55:10 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0 MIME-Version: 1.0 In-Reply-To: <56CEC516.7010306@linux.intel.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25/02/2016 10:10, Xiao Guangrong wrote: > > > On 02/25/2016 04:49 PM, Paolo Bonzini wrote: >> >> >> On 25/02/2016 08:35, Xiao Guangrong wrote: >>>> This may release the mmu_lock before committing the zapping. >>>> Is it safe? If so, we may want to see the reason in the changelog. >>> >>> It is unsafe indeed, please do not do it. >> >> Can you explain why? kvm_zap_obsolete_pages does the same. > > It's not the same, please see the comment in > kvm_mmu_invalidate_zap_all_pages: > /* > * Notify all vcpus to reload its shadow page table > * and flush TLB. Then all vcpus will switch to new > * shadow page table with the new mmu_valid_gen. > * > * Note: we should do this under the protection of > * mmu-lock, otherwise, vcpu would purge shadow page > * but miss tlb flush. > */ > kvm_reload_remote_mmus(kvm); > > That means the tlb is flushed before releasing mmu-lock. > > A example is in rmap_write_protect(), when KVM creates a shadow page > table for > the the guest, it detects no spte pointing to the gfn, so tlb is not > flushed so > that guest can freely updates its pte. Then I'll do a different patch that checks need_resched||spin_needbreak, and if so does commit+cond_resched_lock. I've removed 9/12 from kvm/queue. Again, sorry for giving the impression that these patches were already final. Paolo