[PATCH] flush_dcache_page in get_user_pages()

Davem said:

"Ho hum, it is tricky :-)))

 At bio_map_user() you need to see the user's most recent write to the
 page if you are going "user --> device".  So if "user --> device"
 bio_map_user() must flush_dcache_page().

 I find the write_to_vm condition confusion which is probably why I am
 sitting here spelling this out :-)

 At bio_unmap_user(), if we are going "device --> user" you have to
 flush_dcache_page().  And actually, this flush could just as
 legitimately occur at bio_map_user() time.

 Therefore, the easiest thing to do is always flush_dcache_page() at
 bio_map_user().

 All the other cases are going to be like this, so we might as well
 cut to the chase and flush_dcache_page() for all the pages inside of
 get_user_pages()."

mm/memory.c

@@ -584,6 +584,7 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 					i = -EFAULT;
 					goto out;
 				}
+				flush_dcache_page(pages[i]);
 				if (!PageReserved(pages[i]))
 					page_cache_get(pages[i]);
 			}