LOWPTDI
_Static_assert(PMAP_MAP_LOW == VADDR(LOWPTDI, 0), "PMAP_MAP_LOW");
_Static_assert(LOWPTDI * 2 * NBPDR == KERNBASE,
for (i = 0; i < LOWPTDI; i++)
IdlePTD[i] = enable ? IdlePTD[LOWPTDI + i] : 0;
pmap_cold_mapident(0, atop(NBPDR) * LOWPTDI);
pmap_cold_map(0, NBPDR * LOWPTDI, atop(NBPDR) * LOWPTDI);
PTD[KPTDI] = enable ? PTD[LOWPTDI] : 0;
else if (i == LOWPTDI * NPTEPG)