Re: Page Mapping

Kuas (gmane)
2004-04-05T14:49:10Z

Sorry, please ignore some of the previous question.

I found the answer in Intel Developer guide v3. 'pte_t' consists of the
base physical address of the page (20 MSB of pte_t) and page flags (12
LSB of pte_t). So to get the address, I just have to mask the pte_t with
PAGE_MASK.

Now the next question is can I just use that address and refer to it
right away? Like using a pointer? Or I still have to use some MMU mechanism?

And I don't see anywhere in the page struct to know how big is the page
filled? I don't think every page has all 4 KB filled, right? Or are all
the pages zeroed out before being reassigned? So I still can read the
whole page, just the last bytes will be 0x00 if it's not used.

Kuas.

Kuas (gmane) wrote:
> Hello,
>
> This might be very trivial question for people in this mailing list. I
> need to know if my understanding is correct.
>
> We are doing some experiment with Linux kernel for security. Right now,
> we are trying to see some behavior in the Linux memory management. I am
> trying to track and possibly scan (for now) all the pages that's just
> brought into the memory. I am doing this in i386 arch and Linux kernel
> 2.4.22.
>
> I think it would be good to do it in: mm/memory.c in do_no_page(). At
> the end of the function, I have references to pte_t and page struct of
> the fresh new page that's just brought in from disk (not swapped).
>
> This is diagram the diagram I'm going to refer:
> http://www.skynet.ie/~mel/projects/vm/guide/html/understand/node24.html
>
> From my understanding from the diagram of Linear Address to Page
> conversion (please let me know if I'm correct or misunderstood). The
> struct "pte_t->pte_low" an entry if PTE table, is the base 'physical'
> address of the page. In this case I can just use it to reference the
> page. I can't find any other conversion method to get another address.
>
> Assuming I have that address, can I just direct reference that address
> (assuming the address is physical and from kernel mode) or do I have to
> use some methods to access the page content?
>
> How do I know the size of the page that's filled though? I can't see
> that information from the page struct.
>
> Thanks in Advance for comments and information.
>
>
> Kuas