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>

1 files changed, 3 insertions, 11 deletions

diff --git a/arch/i386/mm/init.c b/arch/i386/mm/init.c
index e1a9a805c445..c3b9905af2d5 100644
--- a/arch/i386/mm/init.c
+++ b/arch/i386/mm/init.c
@@ -800,17 +800,9 @@ void mark_rodata_ro(void)
         unsigned long start = PFN_ALIGN(_text);
         unsigned long size = PFN_ALIGN(_etext) - start;
 
-#ifndef CONFIG_KPROBES
-#ifdef CONFIG_HOTPLUG_CPU
-        /* It must still be possible to apply SMP alternatives. */
-        if (num_possible_cpus() <= 1)
-#endif
-        {
-                change_page_attr(virt_to_page(start),
-                                 size >> PAGE_SHIFT, PAGE_KERNEL_RX);
-                printk("Write protecting the kernel text: %luk\n", size >> 10);
-        }
-#endif
+        change_page_attr(virt_to_page(start),
+                         size >> PAGE_SHIFT, PAGE_KERNEL_RX);
+        printk("Write protecting the kernel text: %luk\n", size >> 10);
         start += size;
         size = (unsigned long)__end_rodata - start;
         change_page_attr(virt_to_page(start),