Xen support

Xen hypervisor support. More...

Topics
	Xen device model
	Manage Xen I/O request servers and related device-model state.
	Xen Dom0 control
	Manage Xen domains and host resources from the privileged domain.
	Xen event channels
	Allocate, bind, and service Xen event channels from Zephyr.
	Xen internal support
	Share low-level helpers used by the Zephyr Xen support code.
	Xen grant tables
	Share memory with foreign domains and map foreign grants.
	Xen HVM operations
	Configure Xen HVM guest parameters through HVM hypercalls.
	Xen memory management
	Manage domain physmaps and Xen-owned resources.
	Xen extended regions
	Allocate, free, and map buffers from Xen extended memory regions.
	Xen version queries
	Query the Xen hypervisor version exposed to the current domain.

Detailed Description

Xen hypervisor support.

Interfaces for running Zephyr as a Xen guest or as Xen Dom0.