From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rusty Russell Subject: Re: [PATCH 0/3] virtio-mmio: handle BE guests on LE hosts Date: Tue, 15 Oct 2013 09:32:47 +1030 Message-ID: <877gdfbgmg.fsf@rustcorp.com.au> References: <1381502171-8187-1-git-send-email-marc.zyngier@arm.com> <20131012182837.GC2089@redhat.com> <525BAA40.8070103@arm.com> <20131014085931.GB30954@redhat.com> <1381741495.3247.18.camel@hornet> <20131014104604.GC30954@redhat.com> <1381747859.3247.33.camel@hornet> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Marc Zyngier , "linux-arm-kernel\@lists.infradead.org" , "kvmarm\@lists.cs.columbia.edu" , "kvm\@vger.kernel.org" To: Pawel Moll , "Michael S. Tsirkin" Return-path: Received: from ozlabs.org ([203.10.76.45]:35731 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757485Ab3JNX10 (ORCPT ); Mon, 14 Oct 2013 19:27:26 -0400 In-Reply-To: <1381747859.3247.33.camel@hornet> Sender: kvm-owner@vger.kernel.org List-ID: Pawel Moll writes: > On Mon, 2013-10-14 at 11:46 +0100, Michael S. Tsirkin wrote: >> What I meant is that under the proposed scheme, users with >> existing v1 drivers must configure a v1 device explicitly. >> >> According to the plan, drivers will be updated so they can >> work with both v1 devices and new v2 devices. >> >> But if you configure a v2 device, old drivers >> will not work. > > That's correct, yes. If qemu 2015(16? 17?).01 will provide v2 devices > only, kernel 3.11 is not going to recognize any of them. > > What will happen in reality, though, is that the implementation of the > Linux v1/v2 driver will pre-date *any* v2 device by far. First > implementation of v1 devices appeared almost 2 years after the driver > appeared. It will take year for people to upgrade to v2, and probably > only after they experience problems with page-based addressing mode. > > I think I can live with this. Yes, this makes sense. In particular, MMIO doesn't have any users you don't control at this point. I expect it to be less than 2 years to get into qemu, but there'll be no compelling reason to use v2 devices for at least that long. Cheers, Rusty.