On 07/01/2011 08:36 AM, Ingo Molnar wrote:

So we could kill multiple birds with the same stone here:

 - remove various ugly uses of /dev/mem (including the rootkit usage),
   with or without strict-devmem

 - extending it to above-4G for inspection purposes

 - allowing to kill /dev/mem access runtime similar to the 
   disable_modules lock-down killswitch, for the so inclined.

Would you be interested in modifying your patch-set in such a 
fashion?

There is another use that I have looked at, as well: for testing
purposes, it would be extremely good to be able to dirty and/or flush an
arbitrary physical cache line for testing purposes.

This is very very similar to /dev/mem usage -- access to an arbitrary
chunk of memory -- and a fully enabled /dev/mem can of course support
this use (just mmap the page with the relevant cache line).  However, it
could also be a separate device which could have looser permissions than
/dev/mem; or a set of ioctls on /dev/mem with a separate kill switch,
because no data would ever be have modified or returned to user space.

Either way, though, we found that it would share a lot of code with the
/dev/mem implementation, and as such fixing up the underlying machinery
is the sanest way to upstream this.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.