Why need the Global Descriptor Table in the kernel?

[Xiangfei Jia <xjianz@xxxxxxxxx>]

On 8086 microprocessors, there are three types of addresses: Logical address, Linear address (or Virtual address),  and 
Physical address. 

Logical addresse contains of a segment (segment identifier) and a
offset. Each segment is represented by a segment descriptor. All these
descriptors are stored either in GDT or LDT. The Linux kernel only has
limited support of semgnets. I also looked at the GDT inside. It seems
that all the segments in the table has the access of the full range of
the memory. BUT, the segments are only useful to allow different
section of memory in a single process. 

My question is (1) does the kernel still use logical address and has to
convert from logcial to linear addresses? (2) why the kernel still use
the GDT, which is not very useful in the kernel?