Re: Page Mapping

["Kuas (gmane)" <ku4s@users.sourceforge.net>]

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

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