Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757165AbZFRSxR (ORCPT ); Thu, 18 Jun 2009 14:53:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753294AbZFRSxH (ORCPT ); Thu, 18 Jun 2009 14:53:07 -0400 Received: from mx2.redhat.com ([66.187.237.31]:54062 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752327AbZFRSxF (ORCPT ); Thu, 18 Jun 2009 14:53:05 -0400 Date: Thu, 18 Jun 2009 11:51:15 -0700 From: Chris Wright To: Muli Ben-Yehuda Cc: Chris Wright , "Yu, Fenghua" , "'David Woodhouse'" , "'Linus Torvalds'" , "'Stephen Rothwell'" , "'Andrew Morton'" , "'Ingo Molnar'" , "Kay, Allen M" , "'lkml'" , "'iommu'" Subject: Re: [PATCH 1/2] IOMMU Identity Mapping Support: iommu_identity_mapping definition Message-ID: <20090618185115.GC2500@x200.localdomain> References: <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> <20090618182545.GC6838@il.ibm.com> <20090618183121.GB2500@x200.localdomain> <20090618184101.GE6838@il.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090618184101.GE6838@il.ibm.com> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1475 Lines: 34 * Muli Ben-Yehuda (muli@il.ibm.com) wrote: > On Thu, Jun 18, 2009 at 11:31:21AM -0700, Chris Wright wrote: > > > The 1-1 mapping is for all the host devices _not_ assigned to > > guests. To eliminate the i/o overhead imposed on all guests not > > using an assigned device or from i/o from host. > > > > It's just the same as VT-d PassThrough mode for hardware that > > doesn't support it. > > Ok, that makes sense. Thanks, Chris. However, that doesn't appear to > be what the patch does---unless I'm misreading, if > iommu_identity_mapping is set, *all* devices get identity Correct (and same as pt mode). Of course, a subsequent device assignement will set that mapping to gpa<->hpa, so you'll get proper isolation for the assigned device. Essentially it's saying the only reason you cared about the IOMMU was for device assignment. > mapping. Instead of a global command line option, we need to provide a > way to enable/disable pt or identity mapping (I agree that the user > shouldn't know or care which is used, the kernel should pick the best > one automatically) on a per BDF basis. Yeah, that's a possible enhancement. Although once you've disabled one device's isolation you've created a hole... thanks, -chris -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/