From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754938Ab2DUDbB (ORCPT ); Fri, 20 Apr 2012 23:31:01 -0400 Received: from mail-pz0-f52.google.com ([209.85.210.52]:60797 "EHLO mail-pz0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751138Ab2DUDa7 (ORCPT ); Fri, 20 Apr 2012 23:30:59 -0400 Message-ID: <4F9229EF.4010506@gmail.com> Date: Sat, 21 Apr 2012 11:30:55 +0800 From: Xiao Guangrong User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.1) Gecko/20120216 Thunderbird/10.0.1 MIME-Version: 1.0 To: Marcelo Tosatti CC: Xiao Guangrong , Avi Kivity , LKML , KVM Subject: Re: [PATCH v3 4/9] KVM: MMU: introduce SPTE_ALLOW_WRITE bit References: <4F911B74.4040305@linux.vnet.ibm.com> <4F911BE7.30206@linux.vnet.ibm.com> <20120420213925.GB13817@amt.cnet> In-Reply-To: <20120420213925.GB13817@amt.cnet> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/21/2012 05:39 AM, Marcelo Tosatti wrote: >> @@ -1177,9 +1178,8 @@ static int kvm_set_pte_rmapp(struct kvm *kvm, unsigned long *rmapp, >> new_spte = *sptep & ~PT64_BASE_ADDR_MASK; >> new_spte |= (u64)new_pfn << PAGE_SHIFT; >> >> - new_spte &= ~PT_WRITABLE_MASK; >> - new_spte &= ~SPTE_HOST_WRITEABLE; >> - new_spte &= ~shadow_accessed_mask; >> + new_spte &= ~(PT_WRITABLE_MASK | SPTE_HOST_WRITEABLE | >> + shadow_accessed_mask | SPTE_ALLOW_WRITE); > > Each bit should have a distinct meaning. Here the host pte is being > write-protected, which means only the SPTE_HOST_WRITEABLE bit > should be cleared. Hmm, it is no problem if SPTE_ALLOW_WRITE is not cleared. But the meaning of SPTE_ALLOW_WRITE will become strange: we will see a spte with spte.SPTE_ALLOW_WRITE = 1 (means the spte is writable on host and guest) and spte.SPTE_HOST_WRITEABLE = 0 (means the spte is read-only on host).