Virtual to physical address translation

Vinny_P · 05-01-2015, 12:50 AM

Hi all,

I have an embedded system running Linux. I would like to translate the virtual addresses to the physical address accessed by the processor.

What I tried:
When in the kernel space (in a kernel module), I used the virt_to_phys function. However, I later found out that this function only translates the virtual address created by kmalloc to physical address. I do have some virtual address created using ioremap that do not work with this function. I found this post: http://stackoverflow.com/questions/6...-kernel-module that states that you need to traverse the page table to reconstruct the physical address.

End goal:
I would like to pass any virtual address to a module and get the physical address translation. I would like virtual address created from kernel space (ioremap and kmalloc) or user space (malloc) to be translated.

I presume there is a function that the kernel uses to make its translation. I would like to hook into this function. I'm looking for guidance and help on this issue.

I am also available for a one-on-one chat if a discussion is needed since the topic is too complex to explain on a forum post.

Thank you in advance.

Vinny_P · 05-01-2015, 03:12 AM

I noticed there is a iopa function that does what I need in the pgtable file. I would need to link this file (and the many other dependent files) to my modules Makefile. Is this a recommended approach? (It doesn't seem very simplistic). I was hoping to hook into this function more easily.

Any comments/suggestions?

Thanks.

Vinny_P · 05-01-2015, 12:23 PM

Here is the solution (snippet of code) from post#2:

Code:

// Address for symbol iopa
#include <linux/kallsyms.h>
#define IOPA_SYM "iopa"

// function address holder
unsigned long (*iopa_ptr)(unsigned long addr);

// in module function (say exit)
static int __init vinny_exit(void)
{
		unsigned long address = 0xF20A0000;//random address
		unsigned long new = iopa_ptr(address);
		printk("VAddr 0x%08lx translates to PAddr 0x%08lx\n", address, new);
}
// in module function (say init)
static int __init vinny_init(void)
{
	int iopa_address = kallsyms_lookup_name(IOPA_SYM);
	printk("Address of %s 0x%08x\n", IOPA_SYM, iopa_address);
	iopa_ptr = (void *) iopa_address;
}

Hope this helps.