Improve robustness of NMI handling, for NMIs recognized in kernel

mode.

- Make the NMI handler run on its own stack (TSS_IST2).
- Store the GSBASE value for each CPU just before the start of
  each NMI stack, permitting efficient retrieval using %rsp-relative
  addressing.
- For NMIs taken from kernel mode, program MSR_GSBASE explicitly
  since one or both of MSR_GSBASE and MSR_KGSBASE can be potentially
  invalid.  The current contents of MSR_GSBASE are saved and restored
  at exit.
- For NMIs handled from user mode, continue to use 'swapgs' to
  load the per-CPU GSBASE.

Reviewed by:	jeff
Debugging help:	jeff
Tested by:	gnn, Artem Belevich <artemb at gmail dot com>

0 files changed, 0 insertions, 0 deletions