While setting up a new SuperMicro SuperServer 5018A-FTN4 with an Intel C2758 CPU for a small lab environment an an issue appeared with VirtualBox. It was reporting that the VT-x processor extension wasn’t available when running on Windows Server 2012 R2.
At the time of writing this Google didn’t have any relevant search results for my configuration but I did find an article that suggested disabling the HardwareVirtEx directive in the virtual machines VirtualBox configuration file. This partially worked but was incredibly slow and the VM guest eventually crashed.
According VirtualBox Support Ticket #10694 other programs can also prevent VirtualBox from accessing the VT-x extensions which cause it to report them as not installed.
The solution was to remove the Hyper-V role because it prevented VirtualBox from utilizing the processor’s VT-x extensions even though I didn’t have any active Hyper-V guests running.