------- Comment From [email protected] 2021-12-06 10:43 EDT-------
The DIAG 318 invocation has been present in the the Linux kernel for some time, 
so it's likely you can pick up any modern kernel release and run with it for 
testing. The only way we can easily observe if the CPNC (diag318 data) has been 
successfully set is by looking at the s390dbf messages for the KVM guest. The 
CPNC will always be 4 (denotes Linux environment).

Another way to check is by running the sync_regs_test under
tools/testing/selftests/kvm/s390x/sync_regs_test. Just running the
kernel self test suite can trigger this.

Lastly, I suppose if you were to create a userspace program that simply
ran the instruction using whatever values you wanted, that could work. I
have not done this myself, so I cannot offer much guidance with this
route other than to suggest looking at function
"setup_control_program_code" in arch/s390/kernel/setup.c

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https://bugs.launchpad.net/bugs/1953338

Title:
  [UBUNTU 20.04] KVM hardware diagnose data improvements for guest
  kernel - qemu part

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