From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755906Ab2ILPsK (ORCPT ); Wed, 12 Sep 2012 11:48:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56349 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755090Ab2ILPsG (ORCPT ); Wed, 12 Sep 2012 11:48:06 -0400 Date: Wed, 12 Sep 2012 12:44:52 -0300 From: Marcelo Tosatti To: Avi Kivity Cc: Xiao Guangrong , LKML , KVM Subject: Re: [PATCH v6 12/12] KVM: indicate readonly access fault Message-ID: <20120912154452.GA19789@amt.cnet> References: <5032F8FD.2020306@linux.vnet.ibm.com> <5032FA78.9040405@linux.vnet.ibm.com> <5034CB60.30107@redhat.com> <5034D4E3.2080801@linux.vnet.ibm.com> <5048AE96.3050909@redhat.com> <5049C4D7.50101@linux.vnet.ibm.com> <20120910223140.GA24275@amt.cnet> <504F01DE.20505@redhat.com> <20120911143901.GA11792@amt.cnet> <5050AB89.20705@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5050AB89.20705@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 12, 2012 at 06:34:33PM +0300, Avi Kivity wrote: > On 09/11/2012 05:39 PM, Marcelo Tosatti wrote: > > On Tue, Sep 11, 2012 at 12:18:22PM +0300, Avi Kivity wrote: > >> > The same can happen with slot deletion, for example. > >> > > >> > Userspace (which performed the modification which can result in faults > >> > to non-existant/read-only/.../new-tag memslot), must handle the faults > >> > properly or avoid the possibility for reference to memslot information > >> > from the past. > >> > > >> > I think its worthwhile to add a note about this in the API > >> > documentation: "The user of this interface is responsible for handling > >> > references to stale memslot information, either by handling > >> > exit notifications which reference stale memslot information or not > >> > allowing these notifications to exist by stopping all vcpus in userspace > >> > before performing modifications to the memslots map". > >> > >> Or we can drop the new interface and rely on userspace to perform the > >> lookup under its own locking rules. > >> > >> It's slow, but writes to ROM or ROM/device are rare anyway. > > > > Lookup what information? > > Where to dispatch the write. > > In fact userspace has to do that anyway if it's a ROM/device. There's > no way userspace can guess that unless we pass in the slot number (which > isn't synchronized with anything). Alright, do you prefer the details of this exit to be worked out later, when necessary, then? That is, not merge this particular patch of the series?