x86: Fix alternatives and kprobes to remap write-protected kernel text

Reenable kprobes and alternative patching when the kernel text is write
protected by DEBUG_RODATA

Add a general utility function to change write protected text.  The new
function remaps the code using vmap to write it and takes care of CPU
synchronization.  It also does CLFLUSH to make icache recovery faster.

There are some limitations on when the function can be used, see the
comment.

This is a newer version that also changes the paravirt_ops code.
text_poke also supports multi byte patching now.

Contains bug fixes from Zach Amsden and suggestions from Mathieu
Desnoyers.

Cc: Jan Beulich <jbeulich@novell.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Mathieu Desnoyers <compudj@krystal.dyndns.org>
Cc: Zach Amsden <zach@vmware.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/asm-i386/alternative.h

@@ -149,4 +149,6 @@ apply_paravirt(struct paravirt_patch_site *start,
 #define __parainstructions_end	NULL
 #endif
 
+extern void text_poke(void *addr, unsigned char *opcode, int len);
+
 #endif /* _I386_ALTERNATIVE_H */

include/asm-x86_64/alternative.h

@@ -154,4 +154,6 @@ apply_paravirt(struct paravirt_patch *start, struct paravirt_patch *end)
 #define __parainstructions_end NULL
 #endif
 
+extern void text_poke(void *addr, unsigned char *opcode, int len);
+
 #endif /* _X86_64_ALTERNATIVE_H */

include/asm-x86_64/pgtable.h

@@ -403,6 +403,8 @@ extern struct list_head pgd_list;
 
 extern int kern_addr_valid(unsigned long addr); 
 
+pte_t *lookup_address(unsigned long addr);
+
 #define io_remap_pfn_range(vma, vaddr, pfn, size, prot)		\
 		remap_pfn_range(vma, vaddr, pfn, size, prot)