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Linux runs a basic sanity test to determine this. See: >> https://github.com/torvalds/linux/blob/master/arch/x86/events/core.c#L268 > > So.. what do we do with all this?  :) > > I kinda see the intention of the original change, but it results in > non-bootable systems (linux too, as I think you demonstrate above). > Because of the sanity test, Linux will boot but not register the "cpu" PMU. Perhaps others should also run a similar sanity test on PMU hardware rather than making assumptions and failing to boot.