VirtualBox and Hyper-V don’t play well together

I have Hyper-V installed on my Windows 8.1 laptop – a Dell Inspiron 15R, for work related tasks. But I also wanted to play with the latest Ubuntu. So i initially tried installing Ubuntu in Hyper-V, but ran into some issue right from the start. I didn’t feel like tracking down that issue, so I just installed VirtualBox, since I’ve used that before and it worked pretty well.

I wanted to run 64-bit Ubuntu and since I have 16 GB of physical memory, also give it 6GB to play with. Well, right out of the gate, upon launching the VM in VirtualBox, it threw an error stating “VT-x is not available”. I googled my system and checked the BIOS and all looked correct – I should have hardware virtualization available and enabled.

So after fighting with that for a while, then giving up for a while, thinking that some mystery hardware issue was preventing me from running anything in VirtualBox, I decided to try 32 bit Ubuntu instead. This is when I also noticed that the drop down in VirtualBox for OS type only listed 32-bit options. So I once again tried launching the VM and once again got the same error – VT-x not available. So next I tried lowering the amount of memory below 4 GB. Then I got a different error – “Couldn’t find the end of CPUID sub-leaves”. This was the key error – a quick Google search revealed that Hyper-V was the cause of my issues with VirtualBox. I could either install an earlier version of VirtualBox, or uninstall Hyper-V. I chose the latter (at least for now) just to see if it worked. It did. Here is the link to the post that had the answer:

So now I am finishing up this post in 64 bit Ubuntu 13.10, and the 64 bit options became available in VirtualBox after uninstalling Hyper-V. I’m also running 6GB of memory for the VM. Hopefully this post will tie the 2 errors (VT-x and CPUID sub leaves) together for the next person. I’ll figure out how to handle the Hyper-V issue later!

UPDATE – I did not know that you cannot have 2 hypervisors, hence my problems above. Hanselman has a workaround posted here – basically a boot option that has Hyper-V turned off.