The current cap_user_rdpmc code seems rather confused to me. On x86, *all* events set cap_user_rdpmc if the global rdpmc control is set. But only x86_pmu events define .event_idx, so amd uncore events won't actually expose their rdpmc index to userspace.
Would it make more sense to add a flag PERF_X86_EVENT_RDPMC_PERMITTED that gets set on all events created while rdpmc == 1, to change x86_pmu_event_idx to do something like: if (event->hw.flags & PERF_X86_EVENT_RDPMC_PERMITTED) return event->hw.event_base_rdpmc + 1; else return 0; and to change arch_perf_update_userpage cap_user_rdpmc to match PERF_X86_EVENT_RDPMC_PERMITTED? Then we could ditch the static key and greatly simplify writes to the rdpmc flag by just counting PERF_X86_EVENT_RDPMC_PERMITTED events. This would be a user-visible change on AMD, and I can't test it. On a semi-related note: would this all be nicer if there were vdso function __u64 __vdso_perf_event__read_count(int fd, void *userpage)? This is very easy to do nowadays. If we got *really* fancy, it would be possible to have an rdpmc_safe in the vdso, which has some benefits, although it would be a bit evil and wouldn't work if userspace tracers like pin are in use. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
