From mboxrd@z Thu Jan  1 00:00:00 1970
From: Muli Ben-Yehuda <muli@il.ibm.com>
Subject: Re: [PATCH qemu-kvm] device assignment: default requires IOMMU
Date: Thu, 24 Dec 2009 09:37:07 +0200
Message-ID: <20091224073706.GA2475@il.ibm.com>
References: <20091223224020.GB3305@sequoia.sous-sol.org>
 <1913B65B-382C-4838-8223-B48246E090F7@suse.de>
 <20091224065123.GD2814@verge.net.au>
 <200912241456.00624.sheng@linux.intel.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Simon Horman <horms@verge.net.au>, Alexander Graf <agraf@suse.de>,
	Chris Wright <chrisw@sous-sol.org>,
	Avi Kivity <avi@redhat.com>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Dmitri Seletski <drjoms@gmail.com>
To: Sheng Yang <sheng@linux.intel.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from mtagate1.de.ibm.com ([195.212.17.161]:37686 "EHLO
	mtagate1.de.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1756818AbZLXHhO (ORCPT <rfc822;kvm@vger.kernel.org>);
	Thu, 24 Dec 2009 02:37:14 -0500
Received: from d12nrmr1607.megacenter.de.ibm.com (d12nrmr1607.megacenter.de.ibm.com [9.149.167.49])
	by mtagate1.de.ibm.com (8.13.1/8.13.1) with ESMTP id nBO7bAYr017370
	for <kvm@vger.kernel.org>; Thu, 24 Dec 2009 07:37:10 GMT
Received: from d12av04.megacenter.de.ibm.com (d12av04.megacenter.de.ibm.com [9.149.165.229])
	by d12nrmr1607.megacenter.de.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id nBO7bA5R1442010
	for <kvm@vger.kernel.org>; Thu, 24 Dec 2009 08:37:10 +0100
Received: from d12av04.megacenter.de.ibm.com (loopback [127.0.0.1])
	by d12av04.megacenter.de.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id nBO7b9bQ020089
	for <kvm@vger.kernel.org>; Thu, 24 Dec 2009 08:37:10 +0100
Content-Disposition: inline
In-Reply-To: <200912241456.00624.sheng@linux.intel.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

On Thu, Dec 24, 2009 at 02:56:00PM +0800, Sheng Yang wrote:

> > > >And, of course, disabling the IOMMU requirement using the old:
> > > >
> > > >  -pcidevice host=[addr],dma=none
> > > >
> > > >or the newer:
> > > >
> > > >  -device pci-assign,host=[addr],iommu=0
> > > >
> > > >will do what it always did (not require an IOMMU, and fail to work
> > > >properly).
> > >
> > > Yay!
> > 
> > Sounds good to me. Though I am curious to know the reasoning
> > behind the current logic.
> > 
> Sounds pretty good. :)
> 
> I think maybe it due to we are interested in implementing PV DMA?

Yes, we are. The current defaults came from the desire to support both
pvdma and also 1-1 host mappings. There were patches floating around
for both. Having said that, I fully agree with this change---the
default should be to require IOMMU. Anything else is "highly
experimental".

Cheers,
Muli