Linux VM UEFI boot "WARNING: BIOS bug: CPU MTRRs don't cover all of memory, losing xxx of RAM"

Products

• VMware vSphere ESXi

Issue/Introduction

Symptoms:

• Only 1TB is shown on OS level although virtual machine is configured with larger than 1TB.
• Issue does not occur when virtual machine is configured with Legacy BIOS.
• In the dmesg in guest OS, you see entries similar to:

WARNING: BIOS bug: CPU MTRRs don't cover all of memory losing xxx of RAM.

Environment

VMware vSphere ESXi 5.5
VMware vSphere ESXi 6.0

Cause

This issue occurs due to a limitation of EFI on 6.0 or earlier and design have changed in ESXi 6.5 or later.

Resolution

To resolve the issue, perform any of the below steps:

• Re-install the OS on virtual machine with Legacy BIOS.

 

• Set disable_mtrr_trim in Guest OS.(Contact the OS vendor to ask how to set this).