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

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

[Michael Chapman]

** Description changed:

  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
+   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
+   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
+   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
+ 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.

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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
  2.4.1 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.

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

[Alexandre Derumier]

Hi,
Proxmox users have reported same bug (qemu 2.5 with pc-i440fc-2.4 not migrating to qemu 2.4.1)

https://forum.proxmox.com/threads/cant-live-migrate-after-dist-
upgrade.26097/

I don't have verified yet, but it seem to be related.

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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
  2.4.1 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.

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

[Laszlo Ersek (Red Hat)]

http://thread.gmane.org/gmane.comp.emulators.qemu/390272/focus=391042

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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
  2.4.1 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.

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

[Laszlo Ersek (Red Hat)]

sent a patch: http://thread.gmane.org/gmane.comp.emulators.qemu/395014

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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
  2.4.1 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.

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

[Laszlo Ersek (Red Hat)]

** Changed in: qemu
       Status: New => In Progress

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Title:
  Unable to migrate pc-i440fx-2.4 KVM guest from QEMU 2.5.0 to QEMU
  2.4.1

Status in QEMU:
  In Progress

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.

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

[Laszlo Ersek (Red Hat)]

Fix committed in e6915b5f3a874a467a9a65f7ec1d6ef8d251a51a.

** Changed in: qemu
       Status: In Progress => Fix Committed

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Title:
  Unable to migrate pc-i440fx-2.4 KVM guest from QEMU 2.5.0 to QEMU
  2.4.1

Status in QEMU:
  Fix Committed

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.

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

[T. Huth]

** Changed in: qemu
       Status: Fix Committed => Fix Released

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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

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.

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

[ChristianEhrhardt]

Note: Also affects Migration Xenial->Trusty (tested and ran into the
same issue, that was how I found the bug) and very likely also
Yakkety->Trusty.

 qemu | 2.0.0+dfsg-2ubuntu1.27   | trusty-security           | source
 qemu | 1:2.5+dfsg-5ubuntu10.4   | xenial-updates            | source

Subscribing server Team to look at this in the scope of the qemu
packaging SRU work for Xenial.

** Also affects: qemu (Ubuntu)
   Importance: Undecided
       Status: New

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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:
  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
  2.4.1 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.

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

[ChristianEhrhardt]

** Changed in: qemu (Ubuntu)
       Status: New => Triaged

** Changed in: qemu (Ubuntu)
   Importance: Undecided => High

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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:
  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.

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

[ChristianEhrhardt]

** Also affects: qemu (Ubuntu Xenial)
   Importance: Undecided
       Status: New

** Changed in: qemu (Ubuntu Xenial)
       Status: New => Triaged

** Changed in: qemu (Ubuntu Xenial)
   Importance: Undecided => High

** Changed in: qemu (Ubuntu)
       Status: Triaged => Fix Released

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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.

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

[Serge Hallyn]

Migrating a VM from xenial -> trusty (or anything moving backward) is
not supported.

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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.

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

[ChristianEhrhardt]

Hi Serge I agree to "created on xenial -> migrating to trusty" not being supported.
I already tended to even say "created on xenial with the Trusty machine type -> migrating to trusty" is not supported as well (at least it is failing for all combos I tried.

But I wonder how far "anything moving backward" should go.

Especially I found that the "created on Trusty, migrated to xenial (works), but later migrated back to trusty (fails)" seems affected by it as well.
I'd have thought that this would be supported. What is you opinion on this more specific case?

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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.

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

[Serge Hallyn]

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.

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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.

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

[Paolo Bonzini]

> Especially I found that the "created on Trusty, migrated to xenial
> (works), but later migrated back to trusty (fails)" seems affected by
> it as well.

The first migration of the t->x->t sequence does not really matter (if
anything it could introduce _more_ bugs!), so if x->t is not supported
then neither is t->x->t.

The upstream QEMU project doesn't have the manpower to test and support
backwards migration.  We try not to break it, and in this case there
was an easy fix and we suggest that Canonical backports it.  However,
in general it's not guaranteed to work.

The fix is commit e6915b5f3a874a467a9a65f7ec1d6ef8d251a51a.

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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.

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

[ChristianEhrhardt]

Serge, Paulo - thank you both!

I already had the patch but I think it was good to discuss and list the
expected behavior not only for me, but for whoever else that comes by
this or a similar case.

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

[ChristianEhrhardt]

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

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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