From mboxrd@z Thu Jan 1 00:00:00 1970 From: "David Woodhouse" Subject: Re: [PATCH v3 0/3] virtio DMA API core stuff Date: Sun, 22 Nov 2015 22:21:37 -0000 Message-ID: <899d2ad12a8a5f8d54f8e08c290101ee.squirrel@twosheds.infradead.org> References: <20151119153821-mutt-send-email-mst@redhat.com> <1447976286.145626.122.camel@infradead.org> <20151120085658-mutt-send-email-mst@redhat.com> <1448207908.89124.54.camel@infradead.org> <20151122231622-mutt-send-email-mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20151122231622-mutt-send-email-mst@redhat.com> 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 To: "Michael S. Tsirkin" Cc: linux-s390 , KVM , Marcel Apfelbaum , Benjamin Herrenschmidt , Sebastian Ott , "linux-kernel@vger.kernel.org" , Andy Lutomirski , Christian Borntraeger , Joerg Roedel , Martin Schwidefsky , Paolo Bonzini , Linux Virtualization , David Woodhouse , Christoph Hellwig List-Id: virtualization@lists.linuxfoundation.org > There's that, and there's an "I care about security, but > do not want to burn up cycles on fake protections that > do not work" case. It would seem to make most sense for this use case simply *not* to expose virtio devices to guests as being behind an IOMMU at all. Sure, there are esoteric use cases where the guest actually nests and runs further guests inside itself and wants to pass through the virtio devices from the real hardware host. But presumably those configurations will have multiple virtio devices assigned by the host anyway, and further tweaking the configuration to put them behind an IOMMU shouldn't be hard. -- dwmw2