x86/mm: factor out of top-down direct mapping setup

Create a new function memory_map_top_down to factor out of the top-down
direct memory mapping pagetable setup.  This is also a preparation for the
following patch, which will introduce the bottom-up memory mapping.  That
said, we will put the two ways of pagetable setup into separate functions,
and choose to use which way in init_mem_mapping, which makes the code more
clear.

Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Toshi Kani <toshi.kani@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Thomas Renninger <trenn@suse.de>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Jiang Liu <jiang.liu@huawei.com>
Cc: Wen Congyang <wency@cn.fujitsu.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: Taku Izumi <izumi.taku@jp.fujitsu.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Nazarewicz <mina86@mina86.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/x86/mm/init.c

@@ -418,27 +418,27 @@ static unsigned long __init get_new_step_size(unsigned long step_size)
 	return step_size << 5;
 }
 
-void __init init_mem_mapping(void)
+/**
+ * memory_map_top_down - Map [map_start, map_end) top down
+ * @map_start: start address of the target memory range
+ * @map_end: end address of the target memory range
+ *
+ * This function will setup direct mapping for memory range
+ * [map_start, map_end) in top-down. That said, the page tables
+ * will be allocated at the end of the memory, and we map the
+ * memory in top-down.
+ */
+static void __init memory_map_top_down(unsigned long map_start,
+				       unsigned long map_end)
 {
-	unsigned long end, real_end, start, last_start;
+	unsigned long real_end, start, last_start;
 	unsigned long step_size;
 	unsigned long addr;
 	unsigned long mapped_ram_size = 0;
 	unsigned long new_mapped_ram_size;
 
-	probe_page_size_mask();
-
-#ifdef CONFIG_X86_64
-	end = max_pfn << PAGE_SHIFT;
-#else
-	end = max_low_pfn << PAGE_SHIFT;
-#endif
-
-	/* the ISA range is always mapped regardless of memory holes */
-	init_memory_mapping(0, ISA_END_ADDRESS);
-
 	/* xen has big range in reserved near end of ram, skip it at first.*/
-	addr = memblock_find_in_range(ISA_END_ADDRESS, end, PMD_SIZE, PMD_SIZE);
+	addr = memblock_find_in_range(map_start, map_end, PMD_SIZE, PMD_SIZE);
 	real_end = addr + PMD_SIZE;
 
 	/* step_size need to be small so pgt_buf from BRK could cover it */
@@ -453,13 +453,13 @@ void __init init_mem_mapping(void)
 	 * end of RAM in [min_pfn_mapped, max_pfn_mapped) used as new pages
 	 * for page table.
 	 */
-	while (last_start > ISA_END_ADDRESS) {
+	while (last_start > map_start) {
 		if (last_start > step_size) {
 			start = round_down(last_start - 1, step_size);
-			if (start < ISA_END_ADDRESS)
-				start = ISA_END_ADDRESS;
+			if (start < map_start)
+				start = map_start;
 		} else
-			start = ISA_END_ADDRESS;
+			start = map_start;
 		new_mapped_ram_size = init_range_memory_mapping(start,
 							last_start);
 		last_start = start;
@@ -470,8 +470,27 @@ void __init init_mem_mapping(void)
 		mapped_ram_size += new_mapped_ram_size;
 	}
 
-	if (real_end < end)
-		init_range_memory_mapping(real_end, end);
+	if (real_end < map_end)
+		init_range_memory_mapping(real_end, map_end);
+}
+
+void __init init_mem_mapping(void)
+{
+	unsigned long end;
+
+	probe_page_size_mask();
+
+#ifdef CONFIG_X86_64
+	end = max_pfn << PAGE_SHIFT;
+#else
+	end = max_low_pfn << PAGE_SHIFT;
+#endif
+
+	/* the ISA range is always mapped regardless of memory holes */
+	init_memory_mapping(0, ISA_END_ADDRESS);
+
+	/* setup direct mapping for range [ISA_END_ADDRESS, end) in top-down*/
+	memory_map_top_down(ISA_END_ADDRESS, end);
 
 #ifdef CONFIG_X86_64
 	if (max_pfn > max_low_pfn) {