How does Linux treat memory above the "mem=" mark?

[Howard, Marc]

Hi,

I have a PPC440GX board with 512M of memory.  I use "mem=496M" boot
argument to keep Linux from using the uppermost 16MB of memory.  That
region of memory is instead used for hardware communications.
Occasionally however the CPU will read/write this space as well.

My questions concerns TLB entries.  How does Linux define this region in
the TLB?  Does it define this region as non-cacheable in the TLB?  If
not, what is the correct way to define an area of memory that is outside
the OS's control as non-cacheable?

Thanks,

Marc W. Howard
marc.howard at kla-tencor.com