40 vs 44 bit memory addressing HP DL580/980

[Alan Cox]

On Mon, Nov 22, 2010 at 6:59 AM, John Baldwin <jhb at freebsd.org> wrote:

> On Sunday, November 21, 2010 8:05:26 pm Sean Bruno wrote:
> > Looks like these HP boxes have the capability to do 44 bit memory
> > addressing if configured to do so from the BIOS.
> >
> > Is anyone interested in any data from that setting?
>
> Does it boot ok? :)  The MTRR code should handle that (there is a CPUID
> field that tells the OS how many bits are significant).  Not sure if there
> are any places in the pmap that assume 40 bits, but a test boot is
> certainly
> worth trying.
>
>
Since we don't boot with 40-bit addressing, I can easily predict the
outcome.  :-)

The trouble with this machine is that the second 128GB of RAM is being
placed between 512G and 1T in the physical address space, which is beyond
the range of the (current) direct map.  So, we take a page fault on the
first access to a page in the second 128GB through the direct map.

Alan