You might ask on #virt for the opinion there, but I don't believe migrating backward is supported in any case. t->x->t doesn't change the fact that there is x->t.
-- 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: Triaged 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
