x86: fix /dev/mem compatibility under PAT

Add ioremap_default(), which gives a sane mapping without worrying about
type conflicts.

Use it in /dev/mem read in place of ioremap(), as with ioremap(),
any mapping of the region (other than UC_MINUS) will cause a conflict
and failure of /dev/mem read.

Should address the vbetest failure reported at:

  http://bugzilla.kernel.org/show_bug.cgi?id=11057

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/mm/ioremap.c

diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 2b2bb3f..d1b8671 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -300,6 +300,29 @@
 }
 EXPORT_SYMBOL(ioremap_cache);
 
+static void __iomem *ioremap_default(resource_size_t phys_addr,
+					unsigned long size)
+{
+	unsigned long flags;
+	void *ret;
+	int err;
+
+	/*
+	 * - WB for WB-able memory and no other conflicting mappings
+	 * - UC_MINUS for non-WB-able memory with no other conflicting mappings
+	 * - Inherit from confliting mappings otherwise
+	 */
+	err = reserve_memtype(phys_addr, phys_addr + size, -1, &flags);
+	if (err < 0)
+		return NULL;
+
+	ret = (void *) __ioremap_caller(phys_addr, size, flags,
+					__builtin_return_address(0));
+
+	free_memtype(phys_addr, phys_addr + size);
+	return (void __iomem *)ret;
+}
+
 /**
  * iounmap - Free a IO remapping
  * @addr: virtual address from ioremap_*
@@ -365,7 +388,7 @@
 	if (page_is_ram(start >> PAGE_SHIFT))
 		return __va(phys);
 
-	addr = (void *)ioremap(start, PAGE_SIZE);
+	addr = (void *)ioremap_default(start, PAGE_SIZE);
 	if (addr)
 		addr = (void *)((unsigned long)addr | (phys & ~PAGE_MASK));