From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH v3 4/9] KVM: MMU: introduce SPTE_ALLOW_WRITE bit Date: Sun, 22 Apr 2012 18:12:55 +0300 Message-ID: <4F941FF7.10808@redhat.com> References: <4F911B74.4040305@linux.vnet.ibm.com> <4F911BE7.30206@linux.vnet.ibm.com> <20120420213925.GB13817@amt.cnet> <4F9229EF.4010506@gmail.com> <20120421042208.GB2763@amt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Xiao Guangrong , Xiao Guangrong , LKML , KVM To: Marcelo Tosatti Return-path: In-Reply-To: <20120421042208.GB2763@amt.cnet> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 04/21/2012 07:22 AM, Marcelo Tosatti wrote: > On Sat, Apr 21, 2012 at 11:30:55AM +0800, Xiao Guangrong wrote: > > 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). > > You are combining gpte writable bit, and host pte writable bit (which > are separate and independent of each other) into one bit. > > SPTE_HOST_WRITEABLE already indicates whether the host pte is writable > or not. Maybe we should rename SPTE_ALLOW_WRITE to SPTE_NOT_SHADOWED (or SPTE_SHADOWED with the opposite meaning). Alternatively, SPTE_MMU_WRITEABLE (complements SPTE_HOST_WRITEABLE). -- error compiling committee.c: too many arguments to function