x86: ioremap_nocache fix

This patch fixes a bug of ioremap_nocache. ioremap_nocache() will call
__ioremap() with flags != 0 to do the real work, which will call
change_page_attr_addr() if phys_addr + size - 1 < (end_pfn_map << PAGE_SHIFT).
But some pages between 0 ~ end_pfn_map << PAGE_SHIFT are not mapped by
identity map, this will make change_page_attr_addr failed.

This patch is based on latest x86 git and has been tested on x86_64 platform.
Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/mm/ioremap_64.c

@@ -41,7 +41,14 @@ ioremap_change_attr(unsigned long phys_addr, unsigned long size,
 	if (phys_addr + size - 1 < (end_pfn_map << PAGE_SHIFT)) {
 		unsigned long npages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 		unsigned long vaddr = (unsigned long) __va(phys_addr);
+		int level;
 
+		/*
+		 * If there is no identity map for this address,
+		 * change_page_attr_addr is unnecessary
+		 */
+		if (!lookup_address(vaddr, &level))
+			return err;
 		/*
  		 * Must use a address here and not struct page because the phys addr
 		 * can be a in hole between nodes and not have an memmap entry.