Task Gate Descriptor
TSS descriptors must reside in the GDT. Task Gate descriptors, on the other hand, may reside in the GDT, an LDT, or the IDT (Interrupt Descriptor Table). Figure 11-1 on page 195 illustrates the format of a Task Gate descriptor. It contains a 16-bit value that selects an entry in the GDT containing a TSS descriptor.
Task Gate Selected by a Far Call/Jump
When a far CALL or a far jump selects a Task Gate descriptor, the DPL of the Task Gate, rather than the DPL of the TSS descriptor, is checked during the privilege level check (the DPL of the TSS is ignored). A task switch occurs if the less-privileged of the RPL or CPL is at least as privileged as the Task Gate's DPL value. As examples:
A Task Gate with a DPL of three permits ...
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