[PATCH 0 of 4 RFC] Kexec path alteration

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

I discovered a triple fault bug in the crash kernel while working on the
wider reentrant NMI/MCE issues discussed on the past few weeks on the
list.

As this is quite a substantial change, I present it here as an RFC ahead
of the longer series for reentrant behaviour (which I am still working
on).

I present patches 2 thru 4 simply as debugging aids for the bug fixed in
patch 1.  I am primarily rally concerned about RFC feedback from patch
1, although comments on patches 2 and 3 will not go amis, as they are
expected to be in the longer reentrant series.

Patch 4 is a debugkey '1' which deliberately creates reentrant NMIs and
stack corruption.  It is not intended for actually committing into the
codebase.

I am at a loss to explain why the triple fault is actually occurring; I
failed to get anything from early printk from the crash kernel, but did
not attempt to debug the extra gubbins which kexec puts in the blob.
The fault however is completely deterministic and can be verified by
commenting out the call to enable_nmis() in machine_kexec()

My setup is xen-unstable, 2.6.32-classic based dom0 and kdump kernels
with kexec-tools 2.0.2

~Andrew