mm: make HASHED_PAGE_VIRTUAL page_address' struct page argument const.

Followup to 33dd4e0ec911 "mm: make some struct page's const" which missed the
HASHED_PAGE_VIRTUAL case.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/hash.h

@@ -63,7 +63,7 @@ static inline u32 hash_32(u32 val, unsigned int bits)
 	return hash >> (32 - bits);
 }
 
-static inline unsigned long hash_ptr(void *ptr, unsigned int bits)
+static inline unsigned long hash_ptr(const void *ptr, unsigned int bits)
 {
 	return hash_long((unsigned long)ptr, bits);
 }

include/linux/mm.h

@@ -737,7 +737,7 @@ static __always_inline void *lowmem_page_address(const struct page *page)
 #endif
 
 #if defined(HASHED_PAGE_VIRTUAL)
-void *page_address(struct page *page);
+void *page_address(const struct page *page);
 void set_page_address(struct page *page, void *virtual);
 void page_address_init(void);
 #endif

mm/highmem.c

@@ -326,7 +326,7 @@ static struct page_address_slot {
 	spinlock_t lock;			/* Protect this bucket's list */
 } ____cacheline_aligned_in_smp page_address_htable[1<<PA_HASH_ORDER];
 
-static struct page_address_slot *page_slot(struct page *page)
+static struct page_address_slot *page_slot(const struct page *page)
 {
 	return &page_address_htable[hash_ptr(page, PA_HASH_ORDER)];
 }
@@ -337,7 +337,7 @@ static struct page_address_slot *page_slot(struct page *page)
  *
  * Returns the page's virtual address.
  */
-void *page_address(struct page *page)
+void *page_address(const struct page *page)
 {
 	unsigned long flags;
 	void *ret;