Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934558Ab3FSLx0 (ORCPT ); Wed, 19 Jun 2013 07:53:26 -0400 Received: from e28smtp09.in.ibm.com ([122.248.162.9]:53782 "EHLO e28smtp09.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934170Ab3FSLxY (ORCPT ); Wed, 19 Jun 2013 07:53:24 -0400 Message-ID: <51C19BA6.2060501@linux.vnet.ibm.com> Date: Wed, 19 Jun 2013 19:53:10 +0800 From: Xiao Guangrong User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130510 Thunderbird/17.0.6 MIME-Version: 1.0 To: Paolo Bonzini CC: gleb@redhat.com, avi.kivity@gmail.com, mtosatti@redhat.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH 2/7] KVM: MMU: document clear_spte_count References: <1371632965-20077-1-git-send-email-xiaoguangrong@linux.vnet.ibm.com> <1371632965-20077-3-git-send-email-xiaoguangrong@linux.vnet.ibm.com> <51C196E9.2080508@redhat.com> In-Reply-To: <51C196E9.2080508@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13061911-2674-0000-0000-0000097B0B89 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1127 Lines: 29 On 06/19/2013 07:32 PM, Paolo Bonzini wrote: > Il 19/06/2013 11:09, Xiao Guangrong ha scritto: >> Document it to Documentation/virtual/kvm/mmu.txt > > While reviewing the docs, I looked at the code. > > Why can't this happen? > > CPU 1: __get_spte_lockless CPU 2: __update_clear_spte_slow > ------------------------------------------------------------------------------ > write low > read count > read low > read high > write high > check low and count > update count > > The check passes, but CPU 1 read a "torn" SPTE. In this case, CPU 1 will read the "new low bits" and the "old high bits", right? the P bit in the low bits is cleared when do __update_clear_spte_slow, i.e, it is not present, so the whole value is ignored. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/