x86: PAT avoid aliasing in /dev/mem read/write

Add xlate and unxlate around /dev/mem read/write. This sets up the mapping
that can be used for /dev/mem read and write without aliasing worries.

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

1 files changed, 29 insertions, 0 deletions

diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 3a4baf95e24d..caac7d5699a7 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -336,6 +336,35 @@ void iounmap(volatile void __iomem *addr)
 }
 EXPORT_SYMBOL(iounmap);
 
+/*
+ * Convert a physical pointer to a virtual kernel pointer for /dev/mem
+ * access
+ */
+void *xlate_dev_mem_ptr(unsigned long phys)
+{
+        void *addr;
+        unsigned long start = phys & PAGE_MASK;
+
+        /* If page is RAM, we can use __va. Otherwise ioremap and unmap. */
+        if (page_is_ram(start >> PAGE_SHIFT))
+                return __va(phys);
+
+        addr = (void *)ioremap(start, PAGE_SIZE);
+        if (addr)
+                addr = (void *)((unsigned long)addr | (phys & ~PAGE_MASK));
+
+        return addr;
+}
+
+void unxlate_dev_mem_ptr(unsigned long phys, void *addr)
+{
+        if (page_is_ram(phys >> PAGE_SHIFT))
+                return;
+
+        iounmap((void __iomem *)((unsigned long)addr & PAGE_MASK));
+        return;
+}
+
 #ifdef CONFIG_X86_32
 
 int __initdata early_ioremap_debug;