[PATCH 0 of 1] Kexec alteration

[Andrew Cooper <andrew.cooper3@citrix.com>]

Hello,

Fixing the root reentrant NMI/MCE issues is quickly turning into a
substantially larger problem than initially thought.

As a result, I have decided to submit the fixes in smaller chunks, in
the hope that they are reviewed and integrated separately.  The first
part is changes to the kexec path, from which I am now happy to drop the
RFC tag.

Please scrutinise carefully.


The vague decided plan going forwards is:

 * Implement spin_{un,}lock_recursive_irq{save,restore}()
 * Audit users of mixed regular/recursive calls on the same spinlock
 * Swap recursive spinlocks to be a separate type
 * Fix the semantics of console_force_unlock
 * Continue audit of NMI and MCE paths, with console semantics fixed
 * {Panic,NMI,MCE}-in-progress flags & reentrancy protection
 * Ability to specify whether iret should be used on trap exit
 * Implement "MCEs never iret, NMIs always iret" policy

The plan for "things I think needs to happen" is:
 * Extend spinlock debugging to know about NMI and MCE contexts
 * Implement strict ordering constraints for spinlock debugging

The "other things needing investigating" list includes:
 * Interaction of paging changes and IDTs while purgatory is changing
   processor modes

~Andrew