Running windows 8.1 64 bit inside virtual box was not completely painless. I had one issue getting it started that really drove me bonkers so I’m documenting the fix. Basically it requires a command line fix. We’ll need the virtual machine’s name so open the terminal and run:

# vboxmanage list vms

It will output the names of the virtual machines and their respective guid:

Example Output: [I named my machine "asinc-win8-64-d"]

"asinc-win8-64-d" {b1a4a89f-5abe-4509-929e-5ab484f9b37b}

You’ll need the name for the next terminal command that actually fixes the problem. Note the command is only 1 line long and ends with [space] then the numeral 1. CMPXCHG16B is all one “word”. Sorry about the formatting…

# vboxmanage setextradata "virtualmachinenamehere" VBoxInternal/CPUM/CMPXCHG16B 1

So after you type that you’ll need to restart virtual box. It should work after that.

Here’s where I found the info if you care. https://forums.virtualbox.org/viewtopic.php?f=1&t=50648