5.1_RC3 on Dell r610 fails

[Mark Davies <mark%ecs.vuw.ac.nz@localhost>]

I have 5.1_RC3/i386 running quite happily on a couple of slightly 
older Dell PowerEdge r610's.  I went to install it on a new R610 and 
the system dies immediately

   [...]
Intel 686-class, 2660Hz 0x20bc2
Fatal protection fault in supervisor mode
Stopped in pid 0.1(system) at netbsd:rdmsr+0x4

backtrace:
rdmsr()
est_init_once()
_run_once()
est_init()
cpu_identify()
cpu_attach()
config_attach_loc()
mpacpi_config_cpu()
acpi_madt_walk()
macpi_scan_apics()
mainbus_attach()
  [...]


This new machine has a Xeon E5640 Quad core processor, otherwise not 
to different to the working ones.

Any suggestions on whats broke, how to fix?

cheers
mark