From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Lutomirski Subject: Re: [PATCH v4 0/4] virtio: Clean up scatterlists and use the DMA API Date: Tue, 28 Jul 2015 09:11:43 -0700 Message-ID: References: <55B73A49.9050206@redhat.com> <1438078345.7562.133.camel@kernel.crashing.org> <55B7799C.3060908@redhat.com> <20150728160358-mutt-send-email-mst@redhat.com> <55B77F8C.7010804@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <55B77F8C.7010804@siemens.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Kiszka Cc: "linux-s390@vger.kernel.org" , Benjamin Herrenschmidt , "Michael S. Tsirkin" , Stefan Hajnoczi , Rusty Russell , xen-devel , Christian Borntraeger , Paolo Bonzini , Cornelia Huck , "linux390@de.ibm.com" , Linux Virtualization List-Id: xen-devel@lists.xenproject.org On Jul 28, 2015 6:11 AM, "Jan Kiszka" wrote: > > On 2015-07-28 15:06, Michael S. Tsirkin wrote: > > On Tue, Jul 28, 2015 at 02:46:20PM +0200, Paolo Bonzini wrote: > >> > >> > >> On 28/07/2015 12:12, Benjamin Herrenschmidt wrote: > >>>>> That is an experimental feature (it's x-iommu), so it can change. > >>>>> > >>>>> The plan was: > >>>>> > >>>>> - for PPC, virtio never honors IOMMU > >>>>> > >>>>> - for non-PPC, either have virtio always honor IOMMU, or enforce that > >>>>> virtio is not under IOMMU. > >>>>> > >>> I dislike having PPC special cased. > >>> > >>> In fact, today x86 guests also assume that virtio bypasses IOMMU I > >>> believe. In fact *all* guests do. > >> > >> This doesn't matter much, since the only guests that implement an IOMMU > >> in QEMU are (afaik) PPC and x86, and x86 does not yet promise any kind > >> of stability. > > > > Hmm I think Jan (cc) said it was already used out there. > > Yes, no known issues with vt-d emulation for almost a year now. Error > reporting could be improved, and interrupt remapping is still missing, > but those are minor issues in this context. > > In my testing setups, I also have virtio devices in use, passed through > to an L2 guest, but only in 1:1 mapping so that their broken IOMMU > support causes no practical problems. > How are you getting 1:1 to work? Is it something that L0 QEMU can advertise to L1? If so, can we just do that unconditionally, which would make my patch work? I have no objection to 1:1 devices in general. It's only devices that the PCI code on the guest identifies as not 1:1 but that are nonetheless 1:1 that cause problems.