Virtual Machines display incorrect or differing CPU models in the Guest OS after live migration.

Products

• VMware vSphere ESXi

Issue/Introduction

Multiple Virtual Machines (VMs) are exhibiting inconsistent CPU models at the Guest OS level (e.g., reporting Intel Xeon E5-2650 v4, Gold 6140, or E5-2683 v4). This discrepancy is observed after the VMs have been live migrated (vMotioned) from a cluster with Enhanced vMotion Compatibility (EVC) enabled to a new destination cluster where all ESXi hosts share an identical CPU model.

Environment

VMware vSphere
VMware vCenter Server
VMware ESXi

Cause

Virtual Machines inherit the CPU model string and instruction set features of the ESXi host on which they were initially powered on. During a live migration (vMotion), the Virtual Machine Monitor (VMM) intentionally preserves this original CPU masking to prevent applications or the guest OS from crashing due to a sudden change in available CPU instructions. As a result, the guest OS will continue to report the legacy CPU model of the source host until the VM undergoes a complete power cycle, which tears down and rebuilds the VMM process on the new host.

Resolution

To resolve the CPU model discrepancy and force the VMs to detect the CPU architecture of the current ESXi hosts:

• Schedule a maintenance window for the affected Virtual Machines.
• Initiate a graceful Shut Down Guest OS for each affected VM. (Note: A standard guest OS reboot/restart is insufficient, as it does not terminate the VMM process on the ESXi host).
• Verify the VMs have reached a completely Powered Off state in the vSphere Client.
• Power On the Virtual Machines.
• Log into the Guest OS and verify that the updated and uniform CPU model is now displayed.

Additional Information

Enhanced vMotion Compatibility (EVC) ensures application stability by establishing a baseline of CPU features across heterogeneous hosts. Hardware changes are only exposed to the guest OS upon a cold boot.