tss for ring0 processes?

[JulienDarc]

Hello,

I perfectly understand the need for a tss in interrupts when switching task in interrupts.
Could someone tell me if i still should bother with it when an interrupt occurs while treating a ring0 process?

I have no userspace yet in my os and I want to validate my understanding.

Thanks a lot

[max]

Hey Julien,

the TSS is only used by the CPU when it has to switch from a higher privilege level (ring 3) to a lower one (ring 0). As a kernel task in ring 0 never does this privilege switch, you won't have to write to the TSS in this case.

Greets,
Max

[JulienDarc]

Thanks Max!

I UUUUUUNDERSSSTTTOOODDD!!!!!

I am so happy i will the whole afternoon

[bluemoon]

Note that intel manual specified a proper procedure to switch CPU mode, which include properly setup TSS. Although you may not observe any issue with bogus TSS since nothing could trigger a task switch, you are not following the manual at your own risk.

By the way, I advice to just do it, it's easy to setup TSS, and you need it anyway with user mode or double fault handler.

[JulienDarc]

Yes you are right and I will set up a tss anyway because it is useful.

Thanks a lot!