From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752574AbYEZEG7 (ORCPT ); Mon, 26 May 2008 00:06:59 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750798AbYEZEGt (ORCPT ); Mon, 26 May 2008 00:06:49 -0400 Received: from mis011-1.exch011.intermedia.net ([64.78.21.128]:48530 "EHLO mis011-1.exch011.intermedia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750701AbYEZEGs (ORCPT ); Mon, 26 May 2008 00:06:48 -0400 From: Amit Shah Organization: Qumranet Inc. To: Muli Ben-Yehuda Subject: Re: [PATCH v2 -mm 0/2] x86: per-device dma_mapping_ops Date: Mon, 26 May 2008 09:39:20 +0530 User-Agent: KMail/1.9.9 Cc: FUJITA Tomonori , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, alexisb@us.ibm.com, andi@firstfloor.org, kvm@vger.kernel.org, avi@qumranet.com References: <1211178689-3507-1-git-send-email-fujita.tomonori@lab.ntt.co.jp> <200805221613.03686.amit.shah@qumranet.com> <20080525072011.GM7334@il.ibm.com> In-Reply-To: <20080525072011.GM7334@il.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200805260939.21320.amit.shah@qumranet.com> X-OriginalArrivalTime: 26 May 2008 04:06:47.0907 (UTC) FILETIME=[EAF98B30:01C8BEE5] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sunday 25 May 2008 12:50:11 Muli Ben-Yehuda wrote: > On Thu, May 22, 2008 at 04:13:02PM +0530, Amit Shah wrote: > > OK; this sounds helpful. the hook can make a hypercall and confirm > > with the host kernel if the device in question is an assigned > > physical device. If yes, we replace the dma_ops. Though, the > > original intent of having stackable ops is that we might want to go > > through the swiotlb in the guest even for an assigned device if the > > guest dma addresses are not in the addressable range of the guest > > chipset. > > > > > created (it works with hot plugging). It enables IOMMUs to set up an > > > appropriate dma_mapping_ops per device. > > > > From what we've discussed so far, it looks like stackable dma ops will > > definitely be needed. Does this patchset provide something that stacking > > won't? > > Yes---this patchset let's you have a per-device dma-ops, whereas with > stackable you only get global dma-ops. I think it's clear we need > both, and I think per-device dma-ops are the first thing that's > needed. Stacking can then be introduced on a per-device basis. When we would want stacking, we'll want it globally and not per-device, isn't it? Or at least for devices on a particular bus. When an IOMMU driver registers itself, it should tell which devices it's interested in (each device behind a bus or by enumerating each device it cares for). This should take care of all the scenarios and we won't have the need for per-device dma_ops. For something like pvdma, we can walk through the list of pci devices and make a hypercall for each of them to get this information and have the pvdma version of dma_ops registered for that device. This sounds like it's per-device dma_ops, but it's not -- internally, the dma operations walk through each of the IOMMUs registered and call them in sequence. Does this work?