Memory-Hotplug: Fix the bug on interface /dev/mem for 64-bit kernel

The new added memory can not be access by interface /dev/mem, because we do not
 update the variable high_memory. This patch add a new e820 entry in e820 table,
 and update max_pfn, max_low_pfn and high_memory.

Memory hotplug still has critical issues for 32-bit kernel, and it is more 
important for 64-bit kernel, we fix it on 64-bit first. We add a function 
update_end_of_memory_vars in file arch/x86/mm/init.c to update these variables.
Signed-off-by: Shaohui Zheng <shaohui.zheng@intel.com>
CC: Andi Kleen <ak@linux.intel.com>
CC: Li Haicheng <haicheng.li@intel.com>
Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>
diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index a1a7876..a9b6bae 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -110,8 +110,8 @@ int __init e820_all_mapped(u64 start, u64 end, unsigned type)
 /*
  * Add a memory region to the kernel e820 map.
  */
-static void __init __e820_add_region(struct e820map *e820x, u64 start, u64 size,
-					 int type)
+static void __meminit __e820_add_region(struct e820map *e820x, u64 start,
+					 u64 size, int type)
 {
 	int x = e820x->nr_map;
 
@@ -126,7 +126,7 @@ static void __init __e820_add_region(struct e820map *e820x, u64 start, u64 size,
 	e820x->nr_map++;
 }
 
-void __init e820_add_region(u64 start, u64 size, int type)
+void __meminit e820_add_region(u64 start, u64 size, int type)
 {
 	__e820_add_region(&e820, start, size, type);
 }
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index d406c52..51ff734 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -1,6 +1,7 @@
 #include <linux/initrd.h>
 #include <linux/ioport.h>
 #include <linux/swap.h>
+#include <linux/bootmem.h>
 
 #include <asm/cacheflush.h>
 #include <asm/e820.h>
@@ -386,3 +387,31 @@ void free_initrd_mem(unsigned long start, unsigned long end)
 	free_init_pages("initrd memory", start, end);
 }
 #endif
+
+/**
+ * After memory hotplug, the variable max_pfn, max_low_pfn and high_memory will
+ * be affected, it will be updated in this function. Memory hotplug does not
+ * make sense on 32-bit kernel, so we do did not concern it in this function.
+ */
+void __meminit __attribute__((weak)) update_end_of_memory_vars(u64 start,
+		u64 size)
+{
+#ifdef CONFIG_X86_64
+	unsigned long limit_low_pfn = 1UL<<(32 - PAGE_SHIFT);
+	unsigned long start_pfn = start >> PAGE_SHIFT;
+	unsigned long end_pfn = PFN_UP(start + size);
+
+	if (end_pfn > max_pfn) {
+		max_pfn = end_pfn;
+		high_memory = (void *)__va(max_pfn * PAGE_SIZE - 1) + 1;
+	}
+
+	/* if add to low memory, update max_low_pfn */
+	if (unlikely(start_pfn < limit_low_pfn)) {
+		if (end_pfn <= limit_low_pfn)
+			max_low_pfn = end_pfn;
+		else
+			max_low_pfn = limit_low_pfn;
+	}
+#endif /* CONFIG_X86_64 */
+}
diff --git a/include/linux/bootmem.h b/include/linux/bootmem.h
index b10ec49..84533a5 100644
--- a/include/linux/bootmem.h
+++ b/include/linux/bootmem.h
@@ -13,6 +13,7 @@
 
 extern unsigned long max_low_pfn;
 extern unsigned long min_low_pfn;
+extern void update_end_of_memory_vars(u64 start, u64 size);
 
 /*
  * highest page
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 030ce8a..cd54ad1 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -523,6 +523,13 @@ int __ref add_memory(int nid, u64 start, u64 size)
 		BUG_ON(ret);
 	}
 
+	printk(KERN_INFO "Adding memory region to e820 table (start:%016Lx, size:%016Lx).\n",
+			 (unsigned long long)start, (unsigned long long)size);
+	e820_add_region(start, size, E820_RAM);
+
+	/* update max_pfn, max_low_pfn and high_memory */
+	update_end_of_memory_vars(start, size);
+
 	goto out;
 
 error: