From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <47974B54.30407@redhat.com> Date: Wed, 23 Jan 2008 15:12:36 +0100 From: Gerd Hoffmann MIME-Version: 1.0 Subject: Re: [kvm-devel] [PATCH] export notifier #1 References: <478E4356.7030303@qumranet.com> <20080117162302.GI7170@v2.random> <478F9C9C.7070500@qumranet.com> <20080117193252.GC24131@v2.random> <20080121125204.GJ6970@v2.random> <4795F9D2.1050503@qumranet.com> <20080122144332.GE7331@v2.random> <20080122200858.GB15848@v2.random> <4797384B.7080200@redhat.com> <20080123131939.GJ26420@sgi.com> In-Reply-To: <20080123131939.GJ26420@sgi.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Robin Holt Cc: Christoph Lameter , Andrea Arcangeli , Andrew Morton , Nick Piggin , linux-mm@kvack.org, Benjamin Herrenschmidt , steiner@sgi.com, linux-kernel@vger.kernel.org, Avi Kivity , kvm-devel@lists.sourceforge.net, daniel.blueman@quadrics.com, Hugh Dickins List-ID: >> That would render the notifies useless for Xen too. Xen needs to >> intercept the actual pte clear and instead of just zapping it use the >> hypercall to do the unmap and release the grant. > > We are tackling that by having our own page table hanging off the > structure representing our seg (thing created when we do the equiv of > your grant call). --verbose please. I don't understand that "own page table" trick. Is that page table actually used by the processor or is it just used to maintain some sort of page list? >> Current implementation uses a new vm_ops operation which is called if >> present instead of doing a ptep_get_and_clear_full(). It is in the >> XenSource tree only, mainline hasn't this yet due to implementing only >> the DomU bits so far. When adding Dom0 support to mainline we'll need >> some way to handle it, and I'd like to see the notifies be designed in a >> way that Xen can simply use them. > > Would the callouts Christoph proposed work for you if you maintained > your own page table and moved them after the callouts the mmu_notifiers > are using. I *think* it would. I'm not that deep in the VM details to be sure though. One possible problem I see is that the hypercall does also tear down the mapping, so this isn't just a notify but also changes the page tables, which could confuse the VM later on when it comes to the actual pte clearing. cheers, Gerd -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org