From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42573) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fqcEc-0003h5-2A for qemu-devel@nongnu.org; Fri, 17 Aug 2018 06:44:02 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fqcEX-0006dy-VS for qemu-devel@nongnu.org; Fri, 17 Aug 2018 06:44:01 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:39030 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fqcEX-0006di-PA for qemu-devel@nongnu.org; Fri, 17 Aug 2018 06:43:57 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 64E8F40241CB for ; Fri, 17 Aug 2018 10:43:57 +0000 (UTC) Date: Fri, 17 Aug 2018 11:43:51 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Message-ID: <20180817104351.GG11124@redhat.com> Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= References: <68a98c1b-e6dd-f2df-1499-17c2b8b583be@redhat.com> <20180817092936.GC11124@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [libvirt] clean/simple Q35 support in libvirt+QEMU for guest OSes that don't support virtio-1.0 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Andrea Bolognani Cc: Laine Stump , Libvirt , qemu list On Fri, Aug 17, 2018 at 12:35:11PM +0200, Andrea Bolognani wrote: > On Fri, 2018-08-17 at 10:29 +0100, Daniel P. Berrang=C3=A9 wrote: > > On Thu, Aug 16, 2018 at 06:20:29PM -0400, Laine Stump wrote: > > > 5) Some guest OSes that we still want to support (and which would > > > otherwise work okay on a Q35 virtual machine) have virtio drivers t= oo > > > old to support virtio-1.0 (CentOS6 and RHEL6 are examples of such O= Ses), > > > but due to the chain of reasons listed above, the "standard" config= for > > > a Q35 guest generated by libvirt doesn't support virtio-0.9, hence > > > doesn't support these guest OSes. > >=20 > > Note when talking about "support" you're really saying it from the > > downstream vendor, specifically RHEL, POV. From upstream or Fedora PO= V > > essentially all x86 OS ever made are in scope for running under QEMU > > if suitable virtual hardware models have been provided. QEMU doesn't > > maintain any whitelist of "supported" OS that differs from what is > > technically capable of being run, in the way downstream vendors do. >=20 > Well, at least in the case of RHEL 6, "not supported" means that it > will not boot at all on q35 with the default guest topology created > by libvirt, so that's not really a downstream-only problem :) I mean from an upstream POV we still support RHEL-6 fine in i440fx, so there's no reason to particularly care about RHEL-6 with q35 upstream. It is only downstream decision to try to force it to use q35, despite it not working right today. > > > C) inside libvirt, the implementation of the "virtio-0.9" model is > > > identical to "virtio", except that the VIR_PCI_CONNECT_TYPE flags f= or > > > these devices contain VIR_PCI_CONNECT_TYPE_PCI rather than > > > VIR_PCI_CONNECT_TYPE_PCIE, resulting in those devices being assigne= d to > > > a legacy PCI slot, and thus they would be transitional mode by defa= ult. > >=20 > > For 'virtio-0.9' libvirt should set "disable-modern=3Dyes" in QEMU ar= gs > >=20 > > For 'virtio-1.0' libvirt should set "disable-legacy=3Dyes" in QEMU ar= gs >=20 > If we decide we want to explicitly spell out the options instead > of relying on QEMU changing behavior based on the slot type, which > is probably a good idea anyway, I think we should have >=20 > virtio-0.9 =3D> disable-legacy=3Dno,disable-modern=3Dno > virtio-1.0 =3D> disable-legacy=3Dyes,disable-modern=3Dno >=20 > There's basically no reason to have a device legacy-only rather > than transitional, and spelling out both options instead of only > one of them just seems more robust. >>From a testing POV it is desirable to be able to have legacy-only. There is also possibility that guest OS impl 1.0 in a buggy manner, so forcing legacy only is desirable. The existing device still already provides a transitional option on i440fx, and on Q35 if you do explicit placement in a PCI slot. So I don't think there's a good reason to have a second transitional device type, especially if we're naming it virtio-0.9, it is rather misleading if it would be in fact able to run virtio-1.0 mode. Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| |: https://libvirt.org -o- https://fstop138.berrange.c= om :| |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :|