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20.14. Hypervisor Features

Hypervisors may allow certain CPU / machine features to be enabled (state='on') or disabled (state='off').

  ...
  <features>
    <pae/>
    <acpi/>
    <apic/>
    <hap/>
    <privnet/>
    <hyperv>
      <relaxed state='on'/>
    </hyperv>
  </features>
  ...
  

Figure 20.20. Hypervisor features

All features are listed within the <features> element, if a <state> is not specified it is disabled. The available features can be found by calling the capabilities XML, but a common set for fully virtualized domains are:

Table 20.11. Hypervisor features elements

StateDescription
<pae>Physical address extension mode allows 32-bit guest virtual machines to address more than 4 GB of memory.
<acpi>Useful for power management, for example, with KVM guest virtual machines it is required for graceful shutdown to work.
<apic>Allows the use of programmable IRQ management. For this element, there is an optional attribute eoi with values on and off which sets the availability of EOI (End of Interrupt) for the guest virtual machine.
<hap>Enables the use of Hardware Assisted Paging if it is available in the hardware.
hypervEnables various features to improve the behavior of guest virtual machines running Microsoft Windows. Using the optional attribute relaxed with values on or off enables or disables the relax constraints on timers