struct svm_softc {
	int	asid;
	long	nptgen[MAXCPU];
};

ASID 0 is reserved for the host.
ASID 1 is reserved for overflow allocation.
ASIDs [2, max_asid) are free for normal guest allocations.

svm_init()
{
	asid_unr = alloc_unr(2, max_asid - 1, NULL);
}

svm_vminit()
{
	asid = alloc_unr(asid_unr);
	if (asid == -1)
		asid = 1;	/* overflow asid */
	sc->asid = asid;
}

{
	disable_gintr();

	/* nested pmap is now active on this 'hostcpu' */
	pmap->pm_active |= (1 << hostcpu);
	
	flush_asid = 0;
	nptgen = pmap->nptgen;

	if (vcpustate->lastcpu != hostcpu)
		flush_asid = 1;

	if (sc->nptgen[hostcpu] != nptgen) {
		flush_asid = 1;
		sc->nptgen[hostcpu] = nptgen;
	}

	if (sc->asid == 1)
		flush_asid = 1;

	if (flush_asid)
		ctrl->tlb_ctrl = TLB_FLUSH_GUEST;
	else
		ctrl->tlb_ctrl = TLB_FLUSH_NOTHING;

	svm_launch();

	/* nested pmap is no longer active on this 'hostcpu' */
	pmap_pm_active &= ~(1 << hostcpu);
}