HWPOISON: Add madvise() based injector for hardware poisoned pages v4

Impact: optional, useful for debugging

Add a new madvice sub command to inject poison for some
pages in a process' address space.  This is useful for
testing the poison page handling.

This patch can allow root to tie up large amounts of memory.
I got feedback from container developers and they didn't see any
problem.

v2: Use write flag for get_user_pages to make sure to always get
a fresh page
v3: Don't request write mapping (Fengguang Wu)
v4: Move MADV_* number to avoid conflict with KSM (Hugh Dickins)

Signed-off-by: Andi Kleen <ak@linux.intel.com>
diff --git a/include/asm-generic/mman-common.h b/include/asm-generic/mman-common.h
index 3b69ad3..c325d1e 100644
--- a/include/asm-generic/mman-common.h
+++ b/include/asm-generic/mman-common.h
@@ -34,6 +34,7 @@
 #define MADV_REMOVE	9		/* remove these pages & resources */
 #define MADV_DONTFORK	10		/* don't inherit across fork */
 #define MADV_DOFORK	11		/* do inherit across fork */
+#define MADV_HWPOISON	100		/* poison a page for testing */
 
 /* compatibility flags */
 #define MAP_FILE	0