The seq_file code already disabled pread/pwrite access,

no need for the mtrr code to check any more.

arch/i386/kernel/cpu/mtrr/if.c

@@ -101,9 +101,6 @@ mtrr_write(struct file *file, const char __user *buf, size_t len, loff_t * ppos)
 
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
-	/*  Can't seek (pwrite) on this device  */
-	if (ppos != &file->f_pos)
-		return -ESPIPE;
 	memset(line, 0, LINE_SIZE);
 	if (len > LINE_SIZE)
 		len = LINE_SIZE;