BASE_FB2
fb_cnattach(tag, BASE_FB2, (void *)BASE_FB);
{ "fb", BASE_FB, BASE_FB2, -1, &elb_fb_tag },
BASE_FB2 + SIZE_FB - 1
ppc4xx_tlb_reserve(BASE_FB2, BASE_FB2, TLB_PG_SIZE, TLB_I | TLB_G);