As said earlier in comment #1, #2 and #3 last working kernel that doesn't crash after disk I/O and boots is kernel-default-4.12.14-lp150.12.16.1. Kernel 4.12.14-lp150.12.19.2 boots but crashes after few minutes of I/O stress. After that it crashes after initrd loading (comment #3). If one uses vanilla kernel RPM then you can use latest build (which is my current goto). Current XEN JeOS 15.0/15.1 qcow2 images doesn't boot they crash also same way.