From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33707) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V9GLf-0002KA-0h for qemu-devel@nongnu.org; Tue, 13 Aug 2013 11:17:33 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1V9GLY-000671-NB for qemu-devel@nongnu.org; Tue, 13 Aug 2013 11:17:26 -0400 Received: from mx1.redhat.com ([209.132.183.28]:26172) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V9GLY-00066h-CS for qemu-devel@nongnu.org; Tue, 13 Aug 2013 11:17:20 -0400 Date: Tue, 13 Aug 2013 18:18:18 +0300 From: "Michael S. Tsirkin" Message-ID: <20130813151817.GA2373@redhat.com> References: <20130813125349.GA28317@redhat.com> <87a9klllyz.fsf@codemonkey.ws> <520A48C0.5000205@redhat.com> <520A4C8C.7090202@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <520A4C8C.7090202@suse.de> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH for-1.6] pc: fix up pc initialization List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Andreas =?iso-8859-1?Q?F=E4rber?= Cc: Anthony Liguori , marcel.a@redhat.com, qemu-devel@nongnu.org, Michael Roth , Gerd Hoffmann , Igor Mammedov , Paolo Bonzini On Tue, Aug 13, 2013 at 05:11:08PM +0200, Andreas F=E4rber wrote: > Am 13.08.2013 16:54, schrieb Paolo Bonzini: > > Il 13/08/2013 16:11, Anthony Liguori ha scritto: > >>>> Fix this up, clean up a trivial code duplication > >>>> and add a comment explaining why we special-case 1.5 > >>>> with respect to pvpanic. > >>>> > >>>> Reported-by: Markus Armbruster > >>>> Signed-off-by: Michael S. Tsirkin > >> Thanks for catching this. I'm a little disturbed by this. I use gi= t-am > >> --3way specifically to avoid problems from fuzzing but I guess merge > >> artifacts are possible. > >> > >=20 > > I wonder if we shouldn't disable pvpanic in 1.5 too, one-off behavior= is > > ugly and likely no one will notice. >=20 > I had rejected the previous attempt to completely disable pvpanic devic= e > because it looked to me as if this compatibility aspect had been > forgotten. I didn't imagine the resulting code to look as ugly though, > with us "skipping" _1_5 to not have 1.5 overwrite has_pvpanic for 1.6+. >=20 > mst suggested to patch stable-1.5 to disable it there, too. I am not > against but have doubts as to how well that works with migration, since > 1.5.3 is still a bit off and I would expect 1.5.2 -> 1.6.0 migration to > work without guest-visible changes... We could argue that having to use > -M pc-i440fx-1.5 we can also expect users to add -device pvpanic; > question would be how to convey that knowledge of > if-you-use-pc-x.y-then-you-also-need-to-do-Z to users, which > compat_props usually handle under the hood. We could misuse > pvpanic.ioport=3D0 for that purpose until we have a better solution. >=20 > Regards, > Andreas Well, in this case then this boils down to 1.5.2 migration being buggy - having a small race (migration during reset) which we can then close with 1.5.3 . I don't think anyone ever triggered this race in practice so I'm not sure whether we should be too worried about this. > --=20 > SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 N=FCrnberg, Germany > GF: Jeff Hawn, Jennifer Guild, Felix Imend=F6rffer; HRB 16746 AG N=FCrn= berg