A system with 8 CMODs can have as much as 6 TB of memory.
Oracle VM 3.2.7 supports a maximum of 4 TB of RAM.
Workaround
To run Oracle VM on a system with more than 4TB of memory, add the following line to the grub.conf file:
xen.gz mem=4096G
For example:
kernel /xen.gz dom0_mem=3152M allowsuperpage dom0_vcpus_pin dom0_max_vcpus=20 crashkernel=256M@128M mem=4096G module /vmlinuz-2.6.39-300.32.6.el5uek ro root=UUID=4adbac6a-fa58-4892-9052-2cca403f7dd0 module /initrd-2.6.39-300.32.6.el5uek.img