[PATCH] resurrect CONFIG_HIGHPTE

Bill Irwin's patch to fix up pte's in highmem.

With CONFIG_HIGHPTE, the direct pte pointer in struct page becomes the
64-bit physical address of the single pte which is mapping this page.

If the page is not PageDirect then page->pte.chain points at a list of
pte_chains, which each now contain an array of 64-bit physical
addresses of the pte's which are mapping the page.

The functions rmap_ptep_map() and rmap_ptep_unmap() are used for
mapping and unmapping the page which backs the target pte.

The patch touches all architectures (adding do-nothing compatibility
macros and inlines).  It generally mangles lots of header files and may
break non-ia32 compiles.  I've had it in testing since 2.5.31.

2 files changed, 13 insertions, 2 deletions

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 370177037315..042e6ddfcf8a 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -26,6 +26,7 @@ static inline void *kmap(struct page *page) { return page_address(page); }
 
 #define kmap_atomic(page, idx)		page_address(page)
 #define kunmap_atomic(addr, idx)	do { } while (0)
+#define kmap_atomic_to_page(ptr)	virt_to_page(ptr)
 
 #endif /* CONFIG_HIGHMEM */
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5e01743a0bc6..4dfac9d2cb5c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -159,9 +159,9 @@ struct page {
 	struct list_head lru;		/* Pageout list, eg. active_list;
 					   protected by zone->lru_lock !! */
 	union {
-		struct pte_chain * chain;	/* Reverse pte mapping pointer.
+		struct pte_chain *chain;/* Reverse pte mapping pointer.
 					 * protected by PG_chainlock */
-		pte_t		 * direct;
+		pte_addr_t direct;
 	} pte;
 	unsigned long private;		/* mapping-private opaque data */
 
@@ -322,6 +322,16 @@ static inline void set_page_zone(struct page *page, unsigned long zone_num)
 #endif /* CONFIG_HIGHMEM || WANT_PAGE_VIRTUAL */
 
 /*
+ * Return true if this page is mapped into pagetables.  Subtle: test pte.direct
+ * rather than pte.chain.  Because sometimes pte.direct is 64-bit, and .chain
+ * is only 32-bit.
+ */
+static inline int page_mapped(struct page *page)
+{
+	return page->pte.direct != 0;
+}
+
+/*
  * Error return values for the *_nopage functions
  */
 #define NOPAGE_SIGBUS	(NULL)