kernel gs base, because %rip is adjusted only on kernel-mode trap caused
by iretq execution. On the other hand, the stack contains (hardware
part of) trap frame from the usermode. As a consequence, checking for
frame mode and doing swapgs causes the kernel to enter trap() with
usermode gs base.
Remove the check for mode and conditional swapgs, we already have right
gs base in the MSR.
Submitted by: Nate Eldredge <neldredge math ucsd edu>
MFC after: 3 days
8ad85ff260