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Hello, i heard that hardware tasking isnt supported in longmode. But on what do i need a 64bit TSS then ?

You need to put cr3 and esp so that the cpu can find the ring0 page directory and stack when jumping to ring0.
It works just like software multitasking in protected mode.

All what you need in 64-bit TSS is :

1. ESP0 - (esp for ring 0)
2. SS0 - (ss for ring 0)

Proper set of this values is needed to normal Long mode operation.