Microcode revision of guest OS is different from Microcode revision of ESXi host

Products

• VMware vSphere ESXi

Issue/Introduction

Microcode revision of guest OS is different from microcode revision of ESXi host.

On linux, microcode revision can be checked by /proc/cpuinfo.

# grep microcode /proc/cpuinfo | head -1
microcode       : 0x5003302

Microcode revision of ESXi host can be checked by vsish command..

# vsish -e cat /hardware/cpu/cpuList/0 | grep "microcode" -A2
   Number of microcode updates:0
   Original Revision:0x05003901
   Current Revision:0x05003901

In this example, 0x5003302 is different from 0x5003901.

Environment

VMware vSphere ESXi

Cause

This could happen when the VM was migrated from a host where the microcode revision is different from microcode revision of the current host.

As of ESXi 6.7 P08, 7.0 U3i, 8.0 or later, ESXi saves and restores microcode revision of VM during vMotion so that the microcode revision won't change after vMotion.

 

If you power on the VM on the host of its microcode revision 0x5003302, and then migrate to the another host of its microcode revision 0x5003901, the VM will persistently recognize its microcode revision as 0x5003302, which is different from the microcode revision of the current host.

Resolution

It's expected behavior and no action is required.