At least patch 1 wants backporting.  Commit e0bb712a28a9 ("x86/ucode: Abort
parallel load early on any control thread error") made the problem easier to
hit, but the bug has been present since the introduction of parallel loading.

Another potential fix would be to have stop_machine_run()'s error value filled
in using cmpxchg.

Andrew Cooper (3):
  x86/ucode: Fix error handling during parallel ucode load
  x86/ucode: Drop structurally unreachable ASSERT()s
  x86/ucode: Create a real type for loading_state

 xen/arch/x86/cpu/microcode/core.c | 37 +++++++++++++++----------------
 1 file changed, 18 insertions(+), 19 deletions(-)

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2.39.5