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Description of problem:

After upgrading a Centos 7.4.1708 KVM server to microcode_ctl 2.1-22.2
containing ucode 06-4f-01, revision 0xb000025, date 2017-11-18 the
server emits machine check exceptions like this approx. two times per hour:

Hardware event. This is not a software error.
MCE 0
CPU 13 BANK 0
TIME 1515150637 Fri Jan  5 12:10:37 2018
MCG status:
MCi status:
Corrected error
Error enabled
MCA: Internal parity error
STATUS 90000040000f0005 MCGSTATUS 0
MCGCAP 7000c16 APICID 26 SOCKETID 1
CPUID Vendor Intel Family 6 Model 79

Socket and core number vary, STATUS is always one of 90000040000f0005,
d0000040000f0005 or d0000080000f0005

I didn't see any crashes on the server or its KVM guests.

Version-Release number of selected component (if applicable):

microcode_ctl 2.1-22.2

How reproducible:

Steps to Reproduce:
1.
2.
3.

Actual results:


Expected results:


Additional info:

After downgrading to microcode_ctl to 2.1-22 the server no longer emits
any machine check exceptions.

Machine is equipped with two Intel(R) Xeon(R) CPU E5-2640 v4 @ 2.40GHz and
serves as base for seven virtual machines, three running Centos-7.4.1708 and
four running Windows Server 2008R2.

With the latest upgrade microcode_ctl 2.1-22.5 got installed.
Microcode is downgraded to revision 0xb000021, date = 2017-03-01.

As expected there are no problems with this microcode.

This bug is resolved and can be closed.