This patch implements the functionality of jumping between the kexeced

kernel and the original kernel.
A new flag for sys_kexec_load named KEXEC_JUMP_BACK is added to

indicate that the loaded kernel image is used for jumping back.
To support jumping between two kernels, before jumping to (executing)

the new kernel and jumping back to the original kernel, the devices

are put into quiescent state, and the state of devices and CPU is

saved. After jumping back from kexeced kernel and jumping to the new

kernel, the state of devices and CPU are restored accordingly. The

devices/CPU state save/restore code of software suspend is called to

implement corresponding function.
To support jumping without reserving memory. One shadow backup page

(source page) is allocated for each page used by new (kexeced) kernel

(destination page). When do kexec_load, the image of new kernel is

loaded into source pages, and before executing, the destination pages

and the source pages are swapped, so the contents of destination pages

are backupped. Before jumping to the new (kexeced) kernel and after

jumping back to the original kernel, the destination pages and the

source pages are swapped too.
A jump back protocol is defined and documented.
Signed-off-by: Huang Ying <ying.huang@intel.com>
---
Index: linux-2.6.23-rc8/arch/i386/kernel/machine_kexec.c

===================================================================

--- linux-2.6.23-rc8.orig/arch/i386/kernel/machine_kexec.c	2007-10-10 10:10:22.000000000 +0800

+++ linux-2.6.23-rc8/arch/i386/kernel/machine_kexec.c	2007-10-10 10:10:27.000000000 +0800

@@ -20,6 +20,7 @@

 #include <asm/cpufeature.h>

 #include <asm/desc.h>

 #include <asm/system.h>

+#include <asm/cacheflush.h>
 #define PAGE_ALIGNED __attribute__ ((__aligned__(PAGE_SIZE)))

 static u32 kexec_pgd[1024] PAGE_ALIGNED;

@@ -83,10 +84,14 @@

  * reboot code buffer to allow us to avoid allocations

  * later.

  *

- * Currently nothing.

+ * Turn off NX bit for ...
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