I backported this and tried my tests again, but this alone isn't sufficient to get the T->X->T working (which is effectively 2.0->2.5->2.0). Wily (2.4) is already out of service, so setting this to won't fix.
Thanks for your guidance, but that now properly known I'll set the Xenial task to won't fix for now. ** Changed in: qemu (Ubuntu Xenial) Status: Triaged => Won't Fix -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1536487 Title: Unable to migrate pc-i440fx-2.4 KVM guest from QEMU 2.5.0 to QEMU 2.4.1 Status in QEMU: Fix Released Status in qemu package in Ubuntu: Fix Released Status in qemu source package in Xenial: Won't Fix Bug description: When migrating a pc-i440fc-2.4 KVM guest from QEMU 2.5.0 to QEMU 2.4.1, the target QEMU errors out: qemu-system-x86_64: error while loading state for instance 0x0 of device 'fw_cfg' This appears to be related to the addition of a DMA interface to fw_cfg last October: http://lists.nongnu.org/archive/html/qemu- devel/2015-10/msg04568.html "info qtree" on the source QEMU shows that the DMA interface for fw_cfg had been enabled: bus: main-system-bus type System ... dev: fw_cfg_io, id "" iobase = 1296 (0x510) dma_iobase = 1300 (0x514) dma_enabled = true Incidentally, this guest had just undergone a migration from QEMU 2.4.1 to QEMU 2.5.0, so it looks like DMA was enabled simply through the migration. It seems to me that the DMA interface for fw_cfg should only be enabled on pc-i440fx-2.5 machines or higher. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1536487/+subscriptions