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>

---
 arch/x86/mm/ioremap_64.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/arch/x86/mm/ioremap_64.c
+++ b/arch/x86/mm/ioremap_64.c
@@ -41,8 +41,15 @@ ioremap_change_attr(unsigned long phys_a
 	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.
 		 */

--
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