ddb(4): "ddb is invoked upon a kernel panic when the sysctl(8) ddb.panic is set to 1".
I belive this value is default. So, kernel should be dropped into ddb on panic. Does it happen? What exactly do you see on screen along with uvm_fault? Do you see whole stacktrace? Check https://www.openbsd.org/ddb.html for "Minimum information for kernel problems" section
