Role of TSS

Originally, Intel designed TSS to switch between multiple tasks in the operating system through this segment.

However, it is said that using this switching task will take a lot of CPU time and break the CPU Flow. Therefore, neither Linux nor Windows uses TSS for switching tasks.

Tss also records the "I/O permission bitmap ".

In addition, the ESP and SS registers of the 0-2 ring are recorded in the TSS. When the outer ring (such as ring3) enters the inner ring (such as ring0), the ESP and SS of the inner ring in the TSS are automatically loaded. Why does TSS not record the ESP and SS of ring3? This is because these are pushed into the stack when the outer ring enters the inner ring. When the outer ring is returned from the inner ring, it is OK to restore from the stack.