e820_host is a Xen-specific option, only available for PV domains, that
provides the domain a virtual e820 memory map based on the host one. It
is enabled with a new Xen hypervisor feature, e.g.

  <features>
    <xen>
      <e820_host state='on'/>
    </xen>
  </features>

e820_host is required when using PCI passthrough and is generally
considered safe for any PV kernel. e820_host is silently ignored if set
in HVM domain configuration. See xl.cfg(5) man page in the Xen
documentation for more details.
Signed-off-by: NMarek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: NJim Fehlig <jfehlig@suse.com>