Can’t Start a VM on Windows Server 2008 R2? Could Be Due to Lack of AVX Support.

I recently ran into a situation where I wasn’t able to start virtual machines on a newly installed Windows Server 2008 R2 computer. After a little research I ran into the following Microsoft Knowledge Base article 2517374:

You cannot start virtual machines on a computer that is running Windows Server 2008 R2 and on which a CPU is installed that supports the AVX feature

Here’s the scenario. I installed Windows Server 2008 R2 on a computer with an Intel CPU that supported the Advanced Vector Extensions (AVX) feature. I installed the Hyper-V server role and then imported a virtual machine. However, when I tried to start the virtual machine I received an error indicating that the virtual machine failed to initialize. I enabled hardware assisted virtualization in the BIOS but that didn’t help. I then found the KB251374 article and discovered that Windows Server 2008 R2 doesn’t support the AVX feature. Luckily, Windows Server 2008 R2 SP1 adds the support for AVX. Because my server was a brand new installation, I hadn’t installed SP1. As soon as I installed SP1 I was able to start the virtual machine.

The KB article also documents a workaround where you can force compatible CPU flags by setting a WMI property. However, the workaround has two issues that makes it a pain in the neck. I recommend you install SP1 rather than messing with a problematic workaround.