From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43329) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bn0aQ-0007sE-3v for qemu-devel@nongnu.org; Thu, 22 Sep 2016 05:46:35 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bn0aO-0006OV-2H for qemu-devel@nongnu.org; Thu, 22 Sep 2016 05:46:33 -0400 Date: Thu, 22 Sep 2016 10:46:26 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20160922094625.GD2085@work-vm> References: <20160922052105.GD7915@in.ibm.com> <20160922053008.GH2085@umbus.fritz.box> <20160922060024.GE7915@in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160922060024.GE7915@in.ibm.com> Subject: Re: [Qemu-devel] pseries-2.6 migration from QEMU-2.6 to QEMU-2.7 broken List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Bharata B Rao Cc: David Gibson , qemu-ppc@nongnu.org, qemu-devel@nongnu.org, "Nikunj A. Dadhania" , clg@kaod.org * Bharata B Rao (bharata@linux.vnet.ibm.com) wrote: > On Thu, Sep 22, 2016 at 03:30:08PM +1000, David Gibson wrote: > > On Thu, Sep 22, 2016 at 10:51:05AM +0530, Bharata B Rao wrote: > > > Hi, > > > > > > Nikunj and I realized that migrating pseries-2.6 guest from QEMU-2.6 > > > to newer QEMU-2.7 is broken like this: > > > > > > qemu-system-ppc64: error while loading state for instance 0x0 of device 'cpu' > > > qemu-system-ppc64: load of migration failed: Invalid argument > > > > > > Bisecting tells us that 4e0806110c8b896ceff3490f15a616e8b3165efe > > > (ppc: Add PPC_64H instruction flag to POWER7 and POWER8) is the > > > first bad commit. Along with this there are other 3 similar commits > > > which add new bits to insns_flags and insns_flags2 fields of POWER7 > > > and POWER8 CPUs. > > > > > > 4e0806110c8b896ceff3490f15a616e8b3165efe Adds PPC_64H to POWER7 and POWER8 > > > dfdd3e43620a6cd4f2be31da5a257c84a16fc000 Adds PPC_64BX to POWER7 > > > b781537560e3b968b6fe1395e3d07bd67f0009ba Adds PPC_CILDST to POWER7 and POWER8 > > > 7778a575c7055276afdd01737e9d1029a65f923d Adds PPC2_PM_ISA206 to POWER7 and POWER8 > > > > > > The flag values are expected to remain same for a machine version for > > > the migration to succeed, but this expectation is broken now. Should > > > we make the addition of these flags conditional on machine type version ? > > > But these flags are part of POWER8 CPU definition which is common for > > > both pseries and upcoming powernv. > > > > Can you step me through how the new flags are breaking the migration? > > It's not immediately obvious to me. > > Here is what I understand. Given below is the pruned vmstate_ppc_cpu > data structure. > > const VMStateDescription vmstate_ppc_cpu = { > .name = "cpu", > .fields = (VMStateField[]) { > /* Sanity checking */ > VMSTATE_UINT64_EQUAL(env.insns_flags, PowerPCCPU), > VMSTATE_UINT64_EQUAL(env.insns_flags2, PowerPCCPU), > VMSTATE_END_OF_LIST() > }, > }; > > When pseries-2.6 guest is started at the source with QEMU-2.6, insns_flags > and insns_flags2 will not have PPC_64H, PPC_64BX, PPC_CILDST, PPC2_PM_ISA206 > set. However at the target when pseries-2.6 guest is started with QEMU-2.7, > these flags will be set. And I believe VMSTATE_UINT64_EQUAL checks above > will cause migration to fail. You might find the first two patches in: https://lists.gnu.org/archive/html/qemu-devel/2016-08/msg03681.html useful in debugging this; it prints the values when the _EQUAL macros fail and prints the field name that fails. Dave > Regards, > Bharata. > > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK