From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752291Ab2LYFGC (ORCPT ); Tue, 25 Dec 2012 00:06:02 -0500 Received: from mx1.redhat.com ([209.132.183.28]:2436 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750732Ab2LYFF7 (ORCPT ); Tue, 25 Dec 2012 00:05:59 -0500 Date: Tue, 25 Dec 2012 07:05:55 +0200 From: Gleb Natapov To: Takuya Yoshikawa Cc: mtosatti@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/7] KVM: Write protect the updated slot only when we start dirty logging Message-ID: <20121225050555.GD29007@redhat.com> References: <20121218162558.65a8bfd3.yoshikawa_takuya_b1@lab.ntt.co.jp> <20121218162647.009f468e.yoshikawa_takuya_b1@lab.ntt.co.jp> <20121224132717.GW17584@redhat.com> <20121225130840.74996653.yoshikawa_takuya_b1@lab.ntt.co.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121225130840.74996653.yoshikawa_takuya_b1@lab.ntt.co.jp> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 25, 2012 at 01:08:40PM +0900, Takuya Yoshikawa wrote: > On Mon, 24 Dec 2012 15:27:17 +0200 > Gleb Natapov wrote: > > > > @@ -6897,7 +6897,14 @@ void kvm_arch_commit_memory_region(struct kvm *kvm, > > > spin_lock(&kvm->mmu_lock); > > > if (nr_mmu_pages) > > > kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages); > > > - kvm_mmu_slot_remove_write_access(kvm, mem->slot); > > > + /* > > > + * Write protect all pages for dirty logging. > > > + * Existing largepage mappings are destroyed here and new ones will > > > + * not be created until the end of the logging. > > > + */ > > > + if ((mem->flags & KVM_MEM_LOG_DIRTY_PAGES) && > > > + !(old.flags & KVM_MEM_LOG_DIRTY_PAGES)) > > > + kvm_mmu_slot_remove_write_access(kvm, mem->slot); > > We should not check old slot flags here or at least check that > > old.npages is not zero. Userspace may delete a slot using old flags, > > then, if new memslot is created with dirty log enabled, it will not be > > protected. > > The flag, KVM_MEM_LOG_DIRTY_PAGES, is explicitely cleared when we > delete a slot to free dirty_bitmap: > > if (!npages) > mem->flags &= ~KVM_MEM_LOG_DIRTY_PAGES; > > So when old.npages is not zero, the second condition must be true. > Right. I was looking for where it is cleared and missed that. > Other parts are doing "if (!slot->dirty_bitmap)" to see if the slot > is in dirty logging mode. If you prefer, we can do the same here. > Does not matter to me. If you think it will be more consistent do it. -- Gleb.