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[Bug 1552592] Re: KVM/QEMU live migration fails with Ubuntu wily kernel 4.2.0-30.35


** Tags added: patch

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  KVM/QEMU live migration fails with Ubuntu wily kernel 4.2.0-30.35

Status in linux package in Ubuntu:

Bug description:
  commit 3f11933efc9ef55ecb2ac7e6d626e8d05a99a4b1 - "KVM: x86: expose
  MSR_TSC_AUX to userspace" from ubuntu-wily master git tree breaks
  KVM/QEMU live migration of host with a graphical user interface.

  == Reproduction ==

  Install kernel with 3f11933efc9ef55ecb2ac7e6d626e8d05a99a4b1 included (Ubuntu-4.2.0-30.35)
  Start VM with GUI
  Start migration (no post copy, same migration as you'd in qemu 2.4)
  When migration has finished and you switch the VNC over to the migration target the VM running but frozen showing the last frame buffer, its also not ping-able (so you ssh session is dead if you used that)

  This is independent of (x86_64) Hardware and Guest OS used and also
  the QEMU cpu type (I used mainly kvm64).

  == Backport Solution ==

  After a reverse bisect on the working 4.4 xenial kernel (where it's
  working with the patch from above) I found the missing part.

  While those two KVM patches listed above were backported/added another on was not, namely:
  81b1b9ca6d5ca5f3ce91c0095402def657cf5db3 (from upstream linus)
  KVM: VMX: Fix host initiated access to guest MSR_TSC_AUX

  As there was a API change I made the rather trivial backport to the
  4.2 kernel and tested it successfully.

  The backported patch is attached to this report.

  Some further information and earlier posts from myself about this issue by can be found here:

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