i386 KEXEC must depend on X86_CMPXCHG64

This patch fixes the following compile error with
CONFIG_X86_CMPXCHG64=n:

<-- snip -->

...
CC arch/i386/kernel/machine_kexec.o
arch/i386/kernel/machine_kexec.c: In function 'identity_map_page':
arch/i386/kernel/machine_kexec.c:78: error: implicit declaration of function 'set_64bit' make[1]: *** [arch/i386/kernel/machine_kexec.o] Error 1

<-- snip -->

@@ -662,7 +662,7 @@
 
 config KEXEC
 	bool "kexec system call (EXPERIMENTAL)"
-	depends on EXPERIMENTAL
+	depends on EXPERIMENTAL && X86_CMPXCHG64
 	help
 	  kexec is a system call that implements the ability to shutdown your
 	  current kernel, and to start another kernel.  It is like a reboot

Good catch but wrong fix. This code works fine on a 386. Or it did last time I tried it.

This dependency only exists if 3 level page tables are configured. CONFIG_X86_PAE

The call to set_64bit is a specialized version of set_pmd. Which also uses set_64_bit. So I don't see how your kernel can even build without this.

The only way I can see this even being selected is building a kernel for a 386 or 486 and wanting pae support. Which won't work on a 386 or a 486. Making it a pointless exercise.

So I think either the pgtable-3level.h needs to fixed, or we just make CONFIG_HIGHME64G depend on CONFIG_X86_CMPXCHG64.

Eric

Sounds reasonable (and sorry for the late answer).

Patch below.

cu
Adrian

<-- snip -->

Due to the usage of set_64bit in include/asm-i386/pgtable-3level.h, HIGHMEM64G must depend on X86_CMPXCHG64.

@@ -442,6 +442,7 @@
 
 config HIGHMEM64G
 	bool "64GB"
+	depends on X86_CMPXCHG64
 	help
 	  Select this if you have a 32-bit processor and more than 4
 	  gigabytes of physical RAM.