4GB of memory and NForce4SLI

I tried currently 2006.0 with kernel 2.6.12.18mdksmp-x86_64 into
a MSI K8N Diamond Plus motherboard with Athlon64-X2 4800. The
motherboard has chipset Nforce4-sli and 4 modules of 1GB each.

Currently the BIOS sees 3328MB of memory and in such way
it correctly boots with 2.6.12.18mdksmp and free shows
3350260 kB free mem with the 'free' command.
How to obtain the rest of 700MB of memory? OK, there is the addressing
space for PCI, etc., but for instance other mobos shows more than 3.3GB.
E.g. on Tyan 2885 I see 4096MB in BIOS and 3559132 with 'free'.

The K8N Diamond has an option in BIOS to "Enable Hardware Memory Hole",
which enable memory remapping around the memory hole. The CPU needed
for this option is at least stepping E0. A64-4800X2 is stepping E6
so should be supported. Once the "Hardware Memory Hole" has been
enabled the BIOS sees 4096MB of memory. But the kernel is no
longer able to boot. Latest logs were:

...
Freeing unused kernel memory: 196k freed
Kernel panic - not syncing: No init found. Try passing init= option to kernel

I tried also with kernel-2.6.14.2mdksmp-x86_64 but same results. Even
with kernel-linus-2.6.16.15mdksmp-x86_64 gives the same (plus error
during 3ware modules scsi probing:

scsi: host 0 channel 0 id 0 lun 0x5a5a5a5a5a5a5a5ahas LUN larger than
currently supported.

Bugs in kernel IOMMU?

Bye
Giuseppe.