Does __KERNEL_DS serve a purpose?

[Andy Lutomirski]

I can't see any reason that we need the __KERNEL_DS segment at all --
I think that everything that uses __KERNEL_DS could use __USER_DS
instead.  Am I missing anything?  This has been bugging me for a
while.

I mulled over this a bit when trying to understand the sysret_ss_attrs
bug and then forgot about it.

--Andy