Re: Scan-before-execute code for FreeMWare

[Kevin P. Lawton]

One more related idea...

If we detect a page has not been modified or
read recently (only executed), we could create
a hash list of the modified bytes, and return
the meta page and unmodified page to the
available page pool (heap).

On the next read/write (not execute), we could
rebuild the unmodified page from the modified+hash-table.

This let's us run execute only code with a price tag
of 1+ pages while still running virtualized code.  The '+'
is the size of the hash-table.

The key is to store enough types of time-stamps.
Since we will receive exceptions upon various events,
it's easy to accumulate this info, such as:

  - when a code page is read/written by guest
  - when another piece of code is prescanned by the monitor
  - when the code was last put into guest execution by
    the monitor.
  - when the page was first put into action
  - maybe some stats like number of reads/writes to page by guest

and of course, other non time-stamp stuff like ring level
and segment size.
  

-Kevin