From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robin Holt Subject: Re: [patch 2/4] mmu_notifier: Callbacks to invalidate address ranges Date: Fri, 1 Feb 2008 18:21:45 -0600 Message-ID: <20080202002145.GA17211@sgi.com> References: <20080201050439.009441434@sgi.com> <20080201050623.344041545@sgi.com> <20080201220952.GA3875@sgi.com> <20080201233528.GE12099@sgi.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Andrea Arcangeli , Peter Zijlstra , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, steiner-sJ/iWh9BUns@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Avi Kivity , kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, daniel.blueman-xqY44rlHlBpWk0Htik3J/w@public.gmane.org, Robin Holt To: Christoph Lameter Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org On Fri, Feb 01, 2008 at 04:05:08PM -0800, Christoph Lameter wrote: > On Fri, 1 Feb 2008, Robin Holt wrote: > > > On Fri, Feb 01, 2008 at 03:19:32PM -0800, Christoph Lameter wrote: > > > On Fri, 1 Feb 2008, Robin Holt wrote: > > > > > > > We are getting this callout when we transition the pte from a read-only > > > > to read-write. Jack and I can not see a reason we would need that > > > > callout. It is causing problems for xpmem in that a write fault goes > > > > to get_user_pages which gets back to do_wp_page that does the callout. > > > > > > Right. You placed it there in the first place. So we can drop the code > > > from do_wp_page? > > > > No, we need a callout when we are becoming more restrictive, but not > > when becoming more permissive. I would have to guess that is the case > > for any of these callouts. It is for both GRU and XPMEM. I would > > expect the same is true for KVM, but would like a ruling from Andrea on > > that. > > do_wp_page is entered when the pte shows that the page is not writeable > and it makes the page writable in some situations. Then we do not > invalidate the remote reference. > > However, when we do COW then a *new* page is put in place of the existing > readonly page. At that point we need to remove the remote pte that is > readonly. Then we install a new pte pointing to a *different* page that is > writable. > > Are you saying that you get the callback when transitioning from a read > only to a read write pte on the *same* page? I believe that is what we saw. We have not put in any more debug information yet. I will try to squeze it in this weekend. Otherwise, I will probably have to wait until early Monday. Thanks Robin ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/