i386: fix iounmap's use of vm_struct's size field

get_vm_area always returns an area with an adjacent guard page.  That guard
page is included in vm_struct.size.  iounmap uses vm_struct.size to
determine how much address space needs to have change_page_attr applied to
it, which will BUG if applied to the guard page.

This patch adds a helper function - get_vm_area_size() in linux/vmalloc.h -
to return the actual size of a vm area, and uses it to make iounmap do the
right thing.  There are probably other places which should be using
get_vm_area_size().

Thanks to Dave Young <hidave.darkstar@gmail.com> for debugging the
problem.

[ Andi, it wasn't clear to me whether x86_64 needs the same fix. ]

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Dave Young <hidave.darkstar@gmail.com>
Cc: Chuck Ebbert <cebbert@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index c2b10ca..89338b4 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -58,6 +58,13 @@ void vmalloc_sync_all(void);
 /*
  *	Lowlevel-APIs (not for driver use!)
  */
+
+static inline size_t get_vm_area_size(const struct vm_struct *area)
+{
+	/* return actual size without guard page */
+	return area->size - PAGE_SIZE;
+}
+
 extern struct vm_struct *get_vm_area(unsigned long size, unsigned long flags);
 extern struct vm_struct *__get_vm_area(unsigned long size, unsigned long flags,
 					unsigned long start, unsigned long end);