[Xenial][PATCH 0/1] x86_max_cores==0 panic on Xen guests

Kamal Mostafa kamal at canonical.com
Wed Mar 28 16:28:16 UTC 2018

BugLink: http://bugs.launchpad.net/bugs/1758869

== SRU ==
Fix "Kernel panic with AWS 4.4.0-1053 / 4.4.0-1015".
Boot-time panic occurs on all c3.large instances, due to a recently
introduced* divide-by-zero which occurs when x86_max_cores contains 0
as is the case in some Xen guest configurations as indicated by this
pre-existing dmesg indicator: "smpboot: x86_max_cores == zero !?!?"

*The divide-by-zero was introduced by mainline commit:
7e702d1 x86/microcode/intel: Extend BDW late-loading further with LLC size check

and fixed (reference https://lkml.org/lkml/2018/2/6/320) by:
a15a753 x86/microcode/AMD: Do not load when running on a hypervisor

This fix patch is currently pending for cc: stable.

== Fix ==
Simple context backport from mainline short circuits code paths through
pre-microcode-loading system checks which are pointless on the guest anyway
since it won't load microcode.  Low regression potential.

Borislav Petkov (1):
  x86/microcode/AMD: Do not load when running on a hypervisor

 arch/x86/kernel/cpu/microcode/core.c | 28 +++++++++++++++++++---------
 1 file changed, 19 insertions(+), 9 deletions(-)


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