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, 27 insertions, 5 deletions

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 964ff3b1cff4..83495885ada0 100644
--- a/drivers/char/mem.c
+++ b/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;