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[Malcolm Scott <launchpad@xxxxxxxxxxx>]

That's the patch which *introduces* the regression.

The missing one is 98dd166ea3a3c3b57919e20d9b0d1237fcd0349d.

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https://bugs.launchpad.net/bugs/1542941

Title:
  Regression: problems migrating recent wily/vivid Xen VMs due to memory
  hotplug fix

Status in linux package in Ubuntu:
  Confirmed

Bug description:
  Commit 633d6f17cd91ad5bf2370265946f716e42d388c6 (aka
  38d30afb12140c0e3a446fe779dc9cd29548f313 in vivid) in Xen domU causes
  high resource requirements in the underlying target dom0 (migrating a
  64-bit domU involves a 1GB malloc in dom0, as well as a lot of
  unnecessary work).

  In my specific case, that 1GB malloc fails as my dom0s aren't big
  enough, causing all migrations to fail with the migrating VM
  suspended.

  This is fixed in commit 98dd166ea3a3c3b57919e20d9b0d1237fcd0349d
  "x86/xen: prepare p2m list for memory hotplug":

  """
  Commit 054954eb051f35e74b75a566a96fe756015352c8 ("xen: switch to linear
  virtual mapped sparse p2m list") introduced a regression regarding to
  memory hotplug for a pv-domain: as the virtual space for the p2m list
  is allocated for the to be expected memory size of the domain only,
  hotplugged memory above that size will not be usable by the domain.

  Correct this by using a configurable size for the p2m list in case of
  memory hotplug enabled (default supported memory size is 512 GB for
  64 bit domains and 4 GB for 32 bit domains).

  Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
  Cc: <stable@xxxxxxxxxxxxxxx> # 3.19+
  Reviewed-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
  Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
  """

  Please consider incorporating 98dd166ea3a3c3b57919e20d9b0d1237fcd0349d
  into the wily and vivid kernels.  Thanks.

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