From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:56550) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1T8q1x-00036G-Fk for qemu-devel@nongnu.org; Tue, 04 Sep 2012 06:06:55 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1T8q1n-0002Sb-Nf for qemu-devel@nongnu.org; Tue, 04 Sep 2012 06:06:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:7736) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1T8q1n-0002SW-Eb for qemu-devel@nongnu.org; Tue, 04 Sep 2012 06:06:39 -0400 Message-ID: <5045D2A8.4020208@redhat.com> Date: Tue, 04 Sep 2012 12:06:32 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <1346640974-30974-1-git-send-email-mmogilvi_qemu@miniinfo.net> <1346640974-30974-6-git-send-email-mmogilvi_qemu@miniinfo.net> <50446D11.5050904@suse.de> <5044C10D.7050600@redhat.com> <87fw6z5d0e.fsf@elfo.mitica> <5044D243.3050506@redhat.com> <5044D2A7.7000609@siemens.com> <5044D36E.3060505@redhat.com> <5044D494.3070304@siemens.com> <5044D78D.1060803@redhat.com> <5044D96C.3000406@redhat.com> <5044DB34.7030305@redhat.com> <5044DBEC.4020601@redhat.com> <5045B8E3.9070305@redhat.com> <5045C6BF.3040207@redhat.com> <5045C7CB.5030307@redhat.com> <5045CBDF.6010203@redhat.com> <5045CF10.9000603@siemens.com> In-Reply-To: <5045CF10.9000603@siemens.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v4 5/5] i8259: fix dynamically masking slave IRQs with IMR register List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka Cc: "quintela@redhat.com" , "qemu-devel@nongnu.org" , =?ISO-8859-1?Q?Andreas_F?= =?ISO-8859-1?Q?=E4rber?= , Avi Kivity , Matthew Ogilvie Il 04/09/2012 11:51, Jan Kiszka ha scritto: >> > >> > I don't mean to say we shouldn't care about them, but there are likely >> > to be a lot more users doing backwards migration than users running >> > those guests, let alone migrating them (forwards or backwards). The >> > pragmatic choice is clear. > BTW, did anyone actually test backward migration recently? I thought to > remember I effectively broke it in 1.1 with some changes to the i8259 > (or was it the PIT?) vmstate, and no one really cared about this or my > first proposals to fix it. Correct: commit ce967e2 (i8254: Rework & fix interaction with HPET in legacy mode, 2012-02-01) bumped the PIT version from 2 to 3. RTC changes will break it more in 1.3. Honestly, backwards migration only works on "enterprise" qemu-kvm because it is tested only there. And so far the only sample across major releases is that RHEL6->RHEL5 migration didn't work. Here the choice is between changing guest behavior by defaulting to 4/2, and always transmitting the subsection by defaulting to 0/0. The latter makes the subsection useless, so at that point we might as well bump the version number and board said flight to the Pacific. Paolo