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>

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;

drivers/char/mem.c

@@ -134,6 +134,10 @@ static inline int range_is_allowed(unsigned long pfn, unsigned long size)
 }
 #endif
 
+void __attribute__((weak)) unxlate_dev_mem_ptr(unsigned long phys, void *addr)
+{
+}
+
 /*
  * This funcion reads the *physical* memory. The f_pos points directly to the 
  * memory location. 
@@ -176,17 +180,25 @@ static ssize_t read_mem(struct file * file, char __user * buf,
 
 		sz = min_t(unsigned long, sz, count);
 
+		if (!range_is_allowed(p >> PAGE_SHIFT, count))
+			return -EPERM;
+
 		/*
 		 * On ia64 if a page has been mapped somewhere as
 		 * uncached, then it must also be accessed uncached
 		 * by the kernel or data corruption may occur
 		 */
 		ptr = xlate_dev_mem_ptr(p);
+		if (!ptr)
+			return -EFAULT;
 
-		if (!range_is_allowed(p >> PAGE_SHIFT, count))
-			return -EPERM;
-		if (copy_to_user(buf, ptr, sz))
+		if (copy_to_user(buf, ptr, sz)) {
+			unxlate_dev_mem_ptr(p, ptr);
 			return -EFAULT;
+		}
+
+		unxlate_dev_mem_ptr(p, ptr);
+
 		buf += sz;
 		p += sz;
 		count -= sz;
@@ -235,22 +247,32 @@ static ssize_t write_mem(struct file * file, const char __user * buf,
 
 		sz = min_t(unsigned long, sz, count);
 
+		if (!range_is_allowed(p >> PAGE_SHIFT, sz))
+			return -EPERM;
+
 		/*
 		 * On ia64 if a page has been mapped somewhere as
 		 * uncached, then it must also be accessed uncached
 		 * by the kernel or data corruption may occur
 		 */
 		ptr = xlate_dev_mem_ptr(p);
+		if (!ptr) {
+			if (written)
+				break;
+			return -EFAULT;
+		}
 
-		if (!range_is_allowed(p >> PAGE_SHIFT, sz))
-			return -EPERM;
 		copied = copy_from_user(ptr, buf, sz);
 		if (copied) {
 			written += sz - copied;
+			unxlate_dev_mem_ptr(p, ptr);
 			if (written)
 				break;
 			return -EFAULT;
 		}
+
+		unxlate_dev_mem_ptr(p, ptr);
+
 		buf += sz;
 		p += sz;
 		count -= sz;

include/asm-x86/io.h

@@ -1,3 +1,6 @@
+#ifndef _ASM_X86_IO_H
+#define _ASM_X86_IO_H
+
 #define ARCH_HAS_IOREMAP_WC
 
 #ifdef CONFIG_X86_32
@@ -5,7 +8,12 @@
 #else
 # include "io_64.h"
 #endif
+
+extern void *xlate_dev_mem_ptr(unsigned long phys);
+extern void unxlate_dev_mem_ptr(unsigned long phys, void *addr);
+
 extern int ioremap_change_attr(unsigned long vaddr, unsigned long size,
 				unsigned long prot_val);
 extern void __iomem *ioremap_wc(unsigned long offset, unsigned long size);
 
+#endif /* _ASM_X86_IO_H */

include/asm-x86/io_32.h

@@ -48,12 +48,6 @@
 
 #include <linux/vmalloc.h>
 
-/*
- * Convert a physical pointer to a virtual kernel pointer for /dev/mem
- * access
- */
-#define xlate_dev_mem_ptr(p)	__va(p)
-
 /*
  * Convert a virtual cached pointer to an uncached pointer
  */

include/asm-x86/io_64.h

@@ -307,12 +307,6 @@ void memset_io(volatile void __iomem *a, int b, size_t c);
 extern int iommu_bio_merge;
 #define BIO_VMERGE_BOUNDARY iommu_bio_merge
 
-/*
- * Convert a physical pointer to a virtual kernel pointer for /dev/mem
- * access
- */
-#define xlate_dev_mem_ptr(p)	__va(p)
-
 /*
  * Convert a virtual cached pointer to an uncached pointer
  */