yia64: Fix show_mem() panic

arch/ia64/mm/contig.c

@@ -46,6 +46,8 @@ show_mem (void)
 	printk("Free swap:       %6dkB\n", nr_swap_pages<<(PAGE_SHIFT-10));
 	i = max_mapnr;
 	while (i-- > 0) {
+		if (!pfn_valid(i))
+			continue;
 		total++;
 		if (PageReserved(mem_map+i))
 			reserved++;

arch/ia64/mm/discontig.c

@@ -499,6 +499,8 @@ void show_mem(void)
 	for_each_pgdat(pgdat) {
 		printk("Node ID: %d\n", pgdat->node_id);
 		for(i = 0; i < pgdat->node_spanned_pages; i++) {
+			if (!ia64_pfn_valid(pgdat->node_start_pfn+i))
+				continue;
 			if (PageReserved(pgdat->node_mem_map+i))
 				reserved++;
 			else if (PageSwapCache(pgdat->node_mem_map+i))

arch/ia64/mm/init.c

@@ -459,8 +459,11 @@ int
 ia64_pfn_valid (unsigned long pfn)
 {
 	char byte;
+	struct page *pg = pfn_to_page(pfn);
 
-	return __get_user(byte, (char *) pfn_to_page(pfn)) == 0;
+	return     (__get_user(byte, (char *) pg) == 0)
+		&& ((((u64)pg & PAGE_MASK) == (((u64)(pg + 1) - 1) & PAGE_MASK))
+			|| (__get_user(byte, (char *) (pg + 1) - 1) == 0));
 }
 EXPORT_SYMBOL(ia64_pfn_valid);