I had filed this as a kernel bug at redhat for F27 and F28. Both bugs have been closed with the following explanation from: Justin M. Forbes email@example.com
"This is actually an issue with the test, and how AMD is working after the spectre/meltdown updates. It needs to be fixed in the test. The issue should be tracked on https://pagure.io/kernel-tests/issues"
See redhat bugs 1546440 and 1591967.
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