Xen provides a number of ``assists'' for guest memory management.
These are available on an ``opt-in'' basis to provide commonly-used
extra functionality to a guest.
vm_assist(unsigned int cmd, unsigned int type)
The cmd parameter describes the action to be taken, whilst the
type parameter describes the kind of assist that is being
referred to. Available commands are as follows:
- VMASST_CMD_enable
- Enable a particular assist type
- VMASST_CMD_disable
- Disable a particular assist type
And the available types are:
- VMASST_TYPE_4gb_segments
- Provide emulated support for
instructions that rely on 4GB segments (such as the techniques used
by some TLS solutions).
- VMASST_TYPE_4gb_segments_notify
- Provide a callback to the
guest if the above segment fixups are used: allows the guest to
display a warning message during boot.
- VMASST_TYPE_writable_pagetables
- Enable writable pagetable
mode - described above.
