From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756181Ab3BVELl (ORCPT ); Thu, 21 Feb 2013 23:11:41 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52392 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756132Ab3BVELc (ORCPT ); Thu, 21 Feb 2013 23:11:32 -0500 Message-ID: <1361506273.2801.327.camel@bling.home> Subject: Re: [PATCH] iommu: making IOMMU sysfs nodes API public From: Alex Williamson To: David Gibson Cc: Alexey Kardashevskiy , Joerg Roedel , Benjamin Herrenschmidt , linux-kernel@vger.kernel.org Date: Thu, 21 Feb 2013 21:11:13 -0700 In-Reply-To: <20130222000415.GI21011@truffula.fritz.box> References: <1360628713.3248.8.camel@bling.home> <1360642004-7419-1-git-send-email-aik@ozlabs.ru> <1360645643.3248.91.camel@bling.home> <511A54DC.9030908@ozlabs.ru> <1360689304.3248.154.camel@bling.home> <5121C709.80007@ozlabs.ru> <1361251440.2801.142.camel@bling.home> <20130219073853.GS21067@truffula.fritz.box> <1361304711.2801.232.camel@bling.home> <20130222000415.GI21011@truffula.fritz.box> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2013-02-22 at 11:04 +1100, David Gibson wrote: > On Tue, Feb 19, 2013 at 01:11:51PM -0700, Alex Williamson wrote: > > On Tue, 2013-02-19 at 18:38 +1100, David Gibson wrote: > > > On Mon, Feb 18, 2013 at 10:24:00PM -0700, Alex Williamson wrote: > > > > On Mon, 2013-02-18 at 17:15 +1100, Alexey Kardashevskiy wrote: > [snip] > > > > Adding the window size to sysfs seems more readily convenient, > > > > but is it so hard for userspace to open the files and call a couple > > > > ioctls to get far enough to call IOMMU_GET_INFO? I'm unconvinced the > > > > clutter in sysfs more than just a quick fix. Thanks, > > > > > > And finally, as Alexey points out, isn't the point here so we know how > > > much rlimit to give qemu? Using ioctls we'd need a special tool just > > > to check the dma window sizes, which seems a bit hideous. > > > > Is it more hideous that using iommu groups to report a vfio imposed > > restriction? Are a couple open files and a handful of ioctls worse than > > code to parse directory entries and the future maintenance of an > > unrestricted grab bag of sysfs entries? > > The fact that the memory is locked is a vfio restriction, but the > actual dma window size is, genuinely, a property of the group. A group is an association of devices based on isolation and visibility. The dma window happens to be associated with a group on your platform, but that's not always the case. This is why I was hoping something in sysfs already reported the dma window so that we could point to it rather than creating an interface where it doesn't really belong. Thanks, Alex