KERNEL_TLS_SEGMENT
#define KERNEL_TLS_SELECTOR ((KERNEL_TLS_SEGMENT << 3) | DPL_KERNEL)
tss->gs = (KERNEL_TLS_SEGMENT << 3);
set_segment_descriptor(&gdt[KERNEL_TLS_SEGMENT],
asm volatile("movw %w0, %%gs" : : "r" (KERNEL_TLS_SEGMENT << 3));