The start-of-day environment for guest operating systems is rather
different to that provided by the underlying hardware. In particular,
the processor is already executing in protected mode with paging
Domain 0 is created and booted by Xen itself. For all subsequent
domains, the analogue of the boot-loader is the domain builder,
user-space software running in domain 0. The domain builder is
responsible for building the initial page tables for a domain and
loading its kernel image at the appropriate virtual address.