Ftrace subtest 'Kprobe event user-memory access' in ubuntu_kernel_selftests fail constantly on ppc64/s390

$ sudo autotest/client/autotest-local autotest/client/tests/ubuntu_kernel_selftests/control
...
15:50:03 INFO | START ubuntu_kernel_selftests.ftrace ubuntu_kernel_selftests.ftrace timestamp=1585237803 timeout=1800 localtime=Mar 26
 15:50:03
...
16:04:54 INFO | ========== Summary ===========
16:04:54 INFO | Sub test case: ftracetest failed.
16:04:54 ERROR| Exception escaping from test:
Traceback (most recent call last):
  File "/home/ubuntu/k-testing/autotest/client/shared/test.py", line 411, in _exec
    _call_test_function(self.execute, *p_args, **p_dargs)
  File "/home/ubuntu/k-testing/autotest/client/shared/test.py", line 823, in _call_test_function
    return func(*args, **dargs)
  File "/home/ubuntu/k-testing/autotest/client/shared/test.py", line 291, in execute
    postprocess_profiled_run, args, dargs)
  File "/home/ubuntu/k-testing/autotest/client/shared/test.py", line 212, in _call_run_once
    self.run_once(*args, **dargs)
  File "/home/ubuntu/k-testing/autotest/client/tests/ubuntu_kernel_selftests/ubuntu_kernel_selftests.py", line 188, in run_once
    raise error.TestError('Test failed for ' + test_name)
TestError: Test failed for ftrace
16:04:54 ERROR| child process failed
16:04:56 INFO | ERROR ubuntu_kernel_selftests.ftrace ubuntu_kernel_selftests.ftrace timestamp=1585238696 localtime=Mar 26 16:04:5
6 Test failed for ftrace
16:04:56 INFO | END ERROR ubuntu_kernel_selftests.ftrace ubuntu_kernel_selftests.ftrace timestamp=1585238696 localtime=Mar 26 16:04:5
6
16:04:56 INFO | END GOOD ---- ---- timestamp=1585238696 localtime=Mar 26 16:04:56
16:04:56 INFO | Report successfully generated at /home/ubuntu/k-testing/autotest/client/results/default/job_report.html

looking at the DEBUG log:

03/26 15:50:15 DEBUG| utils:0153| [stdout] TAP version 13
03/26 15:50:15 DEBUG| utils:0153| [stdout] 1..1
03/26 15:50:15 DEBUG| utils:0153| [stdout] # selftests: ftrace: ftracetest
03/26 15:50:15 DEBUG| utils:0153| [stdout] # === Ftrace unit tests ===
...
03/26 15:56:24 DEBUG| utils:0153| [stdout] # [39] Kprobe event user-memory access [UNRESOLVED]
...
03/26 16:04:52 DEBUG| utils:0153| [stdout] #
03/26 16:04:54 DEBUG| utils:0153| [stdout] #
03/26 16:04:54 DEBUG| utils:0153| [stdout] # # of passed: 85
03/26 16:04:54 DEBUG| utils:0153| [stdout] # # of failed: 0
03/26 16:04:54 DEBUG| utils:0153| [stdout] # # of unresolved: 1
03/26 16:04:54 DEBUG| utils:0153| [stdout] # # of untested: 0
03/26 16:04:54 DEBUG| utils:0153| [stdout] # # of unsupported: 1
03/26 16:04:54 DEBUG| utils:0153| [stdout] # # of xfailed: 1
03/26 16:04:54 DEBUG| utils:0153| [stdout] # # of undefined(test bug): 0
03/26 16:04:54 DEBUG| utils:0153| [stdout] not ok 1 selftests: ftrace: ftracetest # exit=1

https://kernel.ubuntu.com/git/ubuntu/autotest-client-tests.git/commit/?id=a381d47a9004388730e825cd20566ef102a29399