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Unable to migrate pc-i440fx-2.4 KVM guest from QEMU 2.5.0 to QEMU 2.4.1
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 2.4.0 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.
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