MSR_KGSBASE
ASSYM(MSR_KGSBASE, MSR_KGSBASE);
wrmsr(MSR_KGSBASE, 0);
wrmsr(MSR_KGSBASE, 0); /* User value while in the kernel */
wrmsr(MSR_KGSBASE, 0); /* XXX User value while we're in the kernel */
wrmsr(MSR_KGSBASE, gd->gd_user_gs);