Find physical memory address from virtual memory address

Question

• On Unix systems, can I find the physical memory address for a given virtual memory address? If yes, how?

---

The real problem I'm trying to solve is, how can I find out if the OS maps two virtual addresses to the exact same physical region?

Eg in the below smaps example, how do I know if both memory regions are, in fact, physically identical?

cat /proc/<pid>/smaps

...
7f7165d42000-7f7265d42000 r--p 00000000 00:14 641846                     /run/shm/test (deleted)
Size:            4194304 kB
Rss:             4194304 kB
Pss:             2097152 kB
...
VmFlags: rd mr mw me nr sd 
7f7265d42000-7f7365d42000 rw-s 00000000 00:14 641846                     /run/shm/test
Size:            4194304 kB
Rss:             4194304 kB
Pss:             2097152 kB
...
VmFlags: rd wr sh mr mw me ms sd 
...

Bonus: Is there a way to simply do it programmatically in C ?

I tried to look for duplicates but could not find a pertinent one.

Answer 1

On Linux you can do it by parsing files in /proc/<pid> , namely, maps and pagemap . There is a little user-space tool that does it for you here .

Compile it (no special options are needed), run page-types -p <pid> -l -N , find the virtual page address in the first column, read the physical address in the second column.

It should be straightforward to turn this into a library and use programmatically. Bear in mind that some operations of the utility require root access (such as reading /proc/kpageflags ), however, none is needed for this task.