PMAP_ASNGEN_INVALID
pmap->pm_percpu[i].pmc_asngen = PMAP_ASNGEN_INVALID;
KASSERT(ci->ci_asn_gen != PMAP_ASNGEN_INVALID);
pmap->pm_percpu[ci->ci_cpuid].pmc_asngen = PMAP_ASNGEN_INVALID;