6.64 (x86 Only) Maximum Memory to Start a PVM Guest is 470 GB

Although PVM guests are technically capable of running with up to 500,000 MB of virtual memory allocated, as described in Chapter 5, Configuration Limits, attempting to start a PVM Guest with more than 470 GB of memory can cause the virtual machine to crash on boot. This problem does not occur if the PVM Guest is started with 470 GB of memory. You are able to hot-add up to 500 GB virtual memory to the PVM Guest once it is running.

Bug 18538335