[Bug 2048517] Re: EPYC-Rome model without XSAVES may break live migration since the removal of the flag on the physical CPU

[Mauricio Faria de Oliveira]

Hi Giuseppe,

That's good news; thanks for testing!

Yes, that's correct. I'll review the patch for SRU considerations (e.g.,
potential side-effects/regressions for existing users, not always
directly clear from the code changes) and proceed if all is OK.

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

** Changed in: qemu (Ubuntu)
       Status: Incomplete => Invalid

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

** Changed in: nova (Ubuntu)
   Importance: Undecided => Medium

** Changed in: nova (Ubuntu)
     Assignee: (unassigned) => Mauricio Faria de Oliveira (mfo)

** Changed in: qemu (Ubuntu)
     Assignee: Sergio Durigan Junior (sergiodj) => (unassigned)

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https://bugs.launchpad.net/bugs/2048517

Title:
  EPYC-Rome model without XSAVES may break live migration since the
  removal of the flag on the physical CPU

Status in nova package in Ubuntu:
  Triaged
Status in qemu package in Ubuntu:
  Invalid

Bug description:
  The linux kernel upstream disabled XSAVES on AMD EPYC Rome CPUs ([1]). Upstream qemu shortly followed with a patch adding a CPU model version of EPYC-Rome without XSAVES ([2])
  The change in the kernel has been backported to ubuntu focal ([3]).

  Without further workarounds or the adapted CPU model in qemu this will lead to a situation were virtual machines with an EPYC-Rome CPU model created on hypervisors with newer EPYC CPUs will have the XSAVES flag enabled, thus preventing live migration to hypervisors with EPYC Rome CPUs were XSAVES is no longer available.
  Therefore I would like to argue that the patch adapting the CPU model in qemu should also be backported to ubuntu focal.


  
  [1]
  https://lore.kernel.org/all/20230307174643.1240184-1-andrew.cooper3@citrix.com/

  [2]
  https://patchew.org/QEMU/20230524213748.8918-1-davydov-max@yandex-team.ru/

  [3]
  https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2023420

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