This is required since the NX protection proagates from the highest level, enforcing NX on the entire range, independent of whether lower level P*Es have the bit set or not. It might be useful to add a platform specific constant to allow making page tables NX on architectures that have a different behavior.
* Move MiBuildPfnDatabaseFromPageTables into MiBuildPfnDatabase
* Make sure to call MmInitializeProcessAddressSpace() from the x64 version of MiInitMachineDependent()
* Handle result of MmInitializeProcessAddressSpace in MiInitMachineDependent (Should do the same for x86)
* Remove obsolete x64 debug print