From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH v4 0/4] virtio: Clean up scatterlists and use the DMA API Date: Wed, 03 Sep 2014 09:43:59 +0200 Message-ID: <5406C6BF.8040908@redhat.com> References: <1409609814.30640.11.camel@pasglop> <1409691213.30640.37.camel@pasglop> <1409695810.30640.57.camel@pasglop> <1409700010.30640.67.camel@pasglop> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1409700010.30640.67.camel@pasglop> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Archive: List-Post: To: Benjamin Herrenschmidt , Andy Lutomirski Cc: "linux-s390@vger.kernel.org" , Konrad Rzeszutek Wilk , "Michael S. Tsirkin" , Linux Virtualization , Christian Borntraeger , "linux390@de.ibm.com" List-ID: Il 03/09/2014 01:20, Benjamin Herrenschmidt ha scritto: > I wouldn't be so certain, as I said, the way virtio is implemented in > qemu bypass the DMA layer which is where IOMMUs sit. The fact that > currently x86 doesn't put an IOMMU there is not even garanteed, is it ? > What happens if you try to mix and match virtio and other emulated > devices that require the iommu on the same bus ? As far as QEMU is concerned, it's trivial to add a property like "direct-ram-access" that selects whether to bypass the IOMMU or not. And it would have zero performance cost if direct RAM access is enabled, compared to the current code. If possible, I would quirk it in the PPC code. Paolo