From mboxrd@z Thu Jan  1 00:00:00 1970
From: mindentropy@gmail.com (mind entropy)
Date: Sat, 13 Sep 2014 13:32:06 +0530
Subject: On virt_to_phys doubts.
Message-ID: <CAM2a4uxdpPXDhAYBdgntMKRxY7mpAoOM15eXhdXUoCw+5aoLdA@mail.gmail.com>
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

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.