GCPU_SEL
tss->tss_fs = GSEL(GCPU_SEL, SEL_KPL);
setsegment(&ci->ci_gdt[GCPU_SEL].sd, ci, sizeof(struct cpu_info)-1,
setsegment(&ci->ci_gdt[GCPU_SEL].sd, ci, sizeof(struct cpu_info)-1,
setsegment(&cpu_info_primary.ci_gdt[GCPU_SEL].sd, &cpu_info_primary,