Enable PMU counters for User mode access
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Authored by sbilgi_juniper.net on Apr 14 2020, 4:14 PM.

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Reviewers

andrew
stevek
jhibbits
siddharthtuli_gmail.com
manu

Summary

If an application wants to use PMU counters,
one needs to implement a kernel module to enable these counters.
This change implements the code to enable PMU counters for User mode access,
User just needs to add "device pmu_cntr" to enable PMU counters.

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Repository

rS FreeBSD src repository - subversion

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sbilgi_juniper.net created this revision.Apr 14 2020, 4:14 PM

Herald added a reviewer: manu. · View Herald TranscriptApr 14 2020, 4:14 PM

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How does this interact with hwpmc?

We should also consider the security implications if an unprivileged process can program the pmu to trace a privileged process.

sys/arm64/arm64/pmu_enable.c
35–48	These should be in `sys/arm64/include/armreg.h`
51	We don't need this, you can just call `smp_rendezvous` directly.
61	You can use `READ_SPECIALREG` here.
69	You can use `WRITE_SPECIALREG` here.
114–115	How does this work? You are trying to run code on all CPUs before they have started. `SI_SUB_DRIVERS` is before `SI_SUB_SMP` on arm64 as we don't support `EARLY_AP_STARTUP`.