On virt_to_phys doubts.

* On virt_to_phys doubts.
@ 2014-09-13  8:02 mind entropy
  2014-09-13  8:31 ` Miles MH Chen
  0 siblings, 1 reply; 7+ messages in thread
From: mind entropy @ 2014-09-13  8:02 UTC (permalink / raw)
  To: kernelnewbies

Hi,

  I want to know the physical address [just for debugging and info.Not
for DMA etc] of a particular virtual address allocated via kmalloc.

   I am running the below code on S3C2440 with 64MB of RAM. The
/proc/meminfo returns

MemTotal:          59164 kB
MemFree:           35884 kB
MemAvailable:      47148 kB

  I run the following module for printing the addresses. [This module
is only for test. So excuse if I have cut corners].

------------------------------------------------

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/printk.h>
#include <linux/module.h>
#include <linux/gfp.h>
#include <linux/types.h>
#include <linux/mm.h>
#include <linux/mm_types.h>
#include <linux/slab.h>

static int vm_mem_test_init(void)
{

    void *km;

    printk(KERN_ALERT "vm mem test init\n");

    km = kmalloc(1,GFP_KERNEL);

    if(km == NULL) {
        printk(KERN_ALERT "Could not kmalloc\n");
        return -1;
    } else {
        printk(KERN_ALERT "Allocated\n");
        printk(KERN_ALERT "Virtual addr : %x\n",(unsigned int)km);
        printk(KERN_ALERT "Kernel physical addr : 0x%x\n",virt_to_phys(km));
        kfree(km);
    }

  return 0;

}

The output for the following is:

Virtual addr : c2c080e0
Kernel physical addr : 0x32c080e0

-----------------------------------------------------------

The kernel physical address is wrong as I only have 64MB. Should I be
doing a kernel page table walk to get the associated physical address?

Thanks
Gautam.

^ permalink raw reply	[flat|nested] 7+ messages in thread