mmap caching issue on ARM.

This issue observed on ARM, when doing to map kernel allocated memory 

i.e via __get_free_pages.

Kernel module updating some counters are not immediately reflected 

to userspace code.

The following code in the userspace program is used to clear the 

cache after read operation. 

/* community.arm.com */

void clear_arm_cache(const char *start_addr , const char *end_addr)
{ 
 const int syscall = 0xf0002;
 __asm __volatile (
  "mov  r0, %0\n"   
  "mov  r1, %1\n"
  "mov  r7, %2\n"
  "mov     r2, #0x0\n"
  "svc     0x00000000\n"
  :
  : "r" (begin), "r" (end), "r" (syscall)
  : "r0", "r1", "r7"
  );
}