Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752459AbbKWH5H (ORCPT ); Mon, 23 Nov 2015 02:57:07 -0500 Received: from mx1.redhat.com ([209.132.183.28]:33298 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750724AbbKWH5F (ORCPT ); Mon, 23 Nov 2015 02:57:05 -0500 Date: Mon, 23 Nov 2015 09:56:56 +0200 From: "Michael S. Tsirkin" To: David Woodhouse Cc: Andy Lutomirski , Benjamin Herrenschmidt , Christian Borntraeger , Paolo Bonzini , "linux-kernel@vger.kernel.org" , Martin Schwidefsky , Sebastian Ott , linux-s390 , Cornelia Huck , Joerg Roedel , Linux Virtualization , Christoph Hellwig , KVM , Marcel Apfelbaum Subject: Re: [PATCH v3 0/3] virtio DMA API core stuff Message-ID: <20151123095453-mutt-send-email-mst@redhat.com> 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-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1231 Lines: 29 On Sun, Nov 22, 2015 at 10:21:34PM -0000, David Woodhouse wrote: > > > > 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. Unfortunately it's a no-go: this breaks the much less esoteric usecase of DPDK: using virtio devices with userspace drivers. Well - not breaks as such as this doesn't currently work, but this approach would prevent us from making it work. > > -- > dwmw2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/