Windows 2012 R2 Hyper-V Licensing Windows XP, Windows 7, Linux,... Application Server

Hello Hyper-V guys!

I want do deploy a simple Application Server (2 CPUs), where there are some tasks who need to be seperated from OS to OS (So not running on one Host).

I know with a Windows 2012 R2 Windows Server i can set up two Hyper-V VMs.

But i have also a Application that runs on Windows XP (and can't be upgraded) and a Solution in Linux.

If i want to Set up 4 VMs = 2x Windows 2012 R2, 1 XP and 1 Linux on Hyper-V how much Windows-Server 2012 R2 Licenses do i need?

Thank you very much for your help.