cr6
struct ctlreg cr6;
local_ctl_store(6, &cr6);
cr6.val &= ~0xff000000UL;
local_ctl_load(6, &cr6);
struct ctlreg cr6;
local_ctl_store(6, &cr6);
cr6.val |= 0xff000000UL;
local_ctl_load(6, &cr6);