What are the hardware requirements for Hypervisor.framework?

I was planning to use xhyve to virtualise FreeBSD on my early 2009 Mac Pro (eight core) which has a fresh install of El Capitan (with all updates).I installed via homebrew and I get the following error when trying to run:

vmx_init: processor not supported by Hypervisor.framework
Unable to create VM (-85377018)

I have verified that the version of xhyve (0.2.0) works on my 2011 iMac. Having a look I can see that on my iMac hv_support is enabled:

iMac$> sysctl kern.hv_support
kern.hv_support: 1

But on my Mac Pro it is not:

Mac Pro$> sysctl kern.hv_support
kern.hv_support: 0

kern.hv_support is a read-only value so cannot be changed using sysctl.

My Mac Pro has an Intel E5520 which I believe supports Intel VT-d, VT-x, and EPT. Apple also has a page detailing the minimum firmware version and hardware required for VT-x, I’m using a newer Mac Pro than specified and the hardware is the most up to date I can find (MP41.0081.B07).

I can find zero documentation about Hypervisor.framework other than the fact that it is new in Yosemite. I’m unsure whether there is some switch I can toggle to enable this, or whether I am completely scuppered…

Any advice on Hypervisor.framework, or suggestions on getting this working? While the answer “give up, it doesn’t work” might be the correct answer, it would be good to see some documentation backing this up.

Apple's documentation for the Hypervisor framework (https://developer.apple.com/library/mac/documentation/DriversKernelHardware/Reference/Hypervisor/index.html) mentions that the processor needs to support Unrestricted Mode, which is a feature available only on a Westmere or newer generation Intel processor. Seeing as the Westmere generation was released on January of 2010, your Mac Pro most likely doesn't support this.