From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754057AbZFRS27 (ORCPT ); Thu, 18 Jun 2009 14:28:59 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751968AbZFRS2u (ORCPT ); Thu, 18 Jun 2009 14:28:50 -0400 Received: from mtagate1.de.ibm.com ([195.212.17.161]:54859 "EHLO mtagate1.de.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751517AbZFRS2u (ORCPT ); Thu, 18 Jun 2009 14:28:50 -0400 Date: Thu, 18 Jun 2009 21:25:45 +0300 From: Muli Ben-Yehuda To: "Yu, Fenghua" Cc: "'David Woodhouse'" , "'Linus Torvalds'" , "'Stephen Rothwell'" , "'Andrew Morton'" , "'Ingo Molnar'" , "'Christopher Wright'" , "Kay, Allen M" , "'lkml'" , "'iommu'" Subject: Re: [PATCH 1/2] IOMMU Identity Mapping Support: iommu_identity_mapping definition Message-ID: <20090618182545.GC6838@il.ibm.com> References: <20090327212321.070229000@intel.com> <20090416001957.GA1527@linux-os.sc.intel.com> <1240135508.3589.75.camel@macbook.infradead.org> <20090513231351.GA22386@linux-os.sc.intel.com> <1242314271.3393.11.camel@macbook.infradead.org> <20090514175944.GA5168@linux-os.sc.intel.com> <20090618180514.GA24082@linux-os.sc.intel.com> <20090618180835.GB6838@il.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 18, 2009 at 11:14:51AM -0700, Yu, Fenghua wrote: > > > >On Thu, Jun 18, 2009 at 11:05:14AM -0700, Fenghua Yu wrote: > > > >> IOMMU Identity Mapping Support: iommu_identity_mapping definition > >> > >> Identity mapping for IOMMU defines a single domain to 1:1 map all > >> pci devices to all usable memory. > > > >Why use VT-d at all in this case? Do you have a use-case in mind? > > Some users want to use VT-d in KVM but are concerned of DMA > remapping performance. They can use identity mapping and still have > KVM on VT-d. They can also use pass through patch (sent out before) > if hardware supports pass through. Sorry, I must be missing something. For the normal device assignment case, we want the IOMMU page tables to have gpa->hpa mappings rather than the 1-1 identity mapping. How do you envision the 1-1 mapping being used in the device assignment case? Cheers, Muli -- Muli Ben-Yehuda | muli@il.ibm.com | +972-4-8281080 Manager, Virtualization and Systems Architecture Master Inventor, IBM Haifa Research Laboratory