From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexander Graf Subject: Re: [PATCH qemu-kvm] device assignment: default requires IOMMU Date: Mon, 18 Jan 2010 15:18:09 +0100 Message-ID: <4B546DA1.4050107@suse.de> References: <20091223224020.GB3305@sequoia.sous-sol.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Avi Kivity , Marcelo Tosatti , kvm@vger.kernel.org, Dmitri Seletski , Sheng Yang To: Chris Wright Return-path: Received: from cantor2.suse.de ([195.135.220.15]:47055 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751470Ab0AROSP (ORCPT ); Mon, 18 Jan 2010 09:18:15 -0500 In-Reply-To: <20091223224020.GB3305@sequoia.sous-sol.org> Sender: kvm-owner@vger.kernel.org List-ID: Chris Wright wrote: > [ resend, fixing email header, sorry for duplicate ] > > The default mode for device assignment is to rely on an IOMMU for > proper translations and a functioning device in the guest. The current > logic makes this requirement advisory, and simply disables the request > for IOMMU if one is not found on the host. This makes for a confused > user when the device assignment appears to work, but the device in the > guest is not functioning (I've seen about a half-dozen reports with > this failure mode). > > Change the logic such that the default requires the IOMMU. Period. > If the host does not have an IOMMU, device assignment will fail. > > This is a user visible change, however I think the current situation is > simply broken. > > 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). > Avi, could you please cherry-pick this into 0.12-stable? I don't feel too eager getting 500 bug reports from people who try out device passthrough with disabled or no IOMMU. Alex