I minimised my qemu-system-arm issue with the mps3-an524 machine.

https://gist.github.com/thejpster/965006cffc6df5325b0742f18586efc7

Basically do a SEV and you'll get a fault, and touch the stack in the fault handler and it'll explode.

But connect GDB and it's fine.

My money is still on the second core waiting in a WFE then it comes up with a bad stack pointer, enters the fault handler, and pushes to to a bad stack pointer. But I have no idea what you're supposed to do to initialise the second processor.