[XenAccess-devel] process-data example and Page Tables

[Matthew D. <ma...@at...>]

Do page tables store virtual or physical addresses?

So for a process (with PAE enabled) CR3 is the physical address of the page
directory pointer (PDP) table (let's say 0x69C0020).  You take the last
couple bits from the virtual address, multiply that by the size of an entry
in the PDP (8 bytes) and you have the offset into the table (0x8), so the
eight bytes at 0x69C0028 is an address to page directory.  Is that address a
virtual address or a physical address?

As I mentioned before, the process-data example program isn't working
correctly.  The problem seems to be when it is translating the virtual
address of the PEB.  It gets the EPROCESS block without a problem, and gets
the value of CR3/DirectoryTableBase (x69C0020).  It then converts that
address to the virtual address (x865c0020), gets the offset (0x8) into the
page directory pointer table and adds it to the virtual address, ending up
with x865C0028.  The problem comes when it tries to look up 0x865C0028; it
tries to look up the address (with xa_read_long_long_virt()) with a PID of 0
(System Idle Process) and can't find it.  

If the page tables know physical addresses, it seems the physical - virtual
- physical translations are unnecessary.

Thanks
-matthew