Ubuntu
qemu package

  1. Bug #1536487
  2. Comment #0

Comment 0 for bug 1536487

Revision history for this message
Michael Chapman (mchapman) wrote :

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.