[Qemu-devel] [Bug 1536487] [NEW] Unable to migrate pc-i440fx-2.4 KVM guest from QEMU 2.5.0 to QEMU 2.4.1

[Michael Chapman]

Public bug reported:

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.

** Affects: qemu
     Importance: Undecided
         Status: New

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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:
  New

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
  2.4.0 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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