[RFC PATCH v2 0/2] x86/perf/amd: AMD PMC counters and NMI latency

[Lendacky, Thomas]

This patch series addresses issues with increased NMI latency in newer
AMD processors that can result in unknown NMI messages when PMC counters
are active.

The following fixes are included in this series:

- Resolve a race condition when disabling an overflowed PMC counter,
  specifically when updating the PMC counter with a new value.
- Resolve handling of multiple active PMC counter overflows in the perf
  NMI handler and when to report that the NMI is not related to a PMC.

If everything looks ok, I'll re-submit without the RFC tag. Definitely
looks cleaner with the AMD specific callback functions.

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Changes from v1 (based on feedback from Peter Z):
- Created an AMD specific disable_all callback function to handle the
  disabling of the counters and resolve the race condition
- Created an AMD specific handle_irq callback function that invokes the
  common x86_pmu_handle_irq() function and then performs the NMI latency
  mitigation.
- Take into account the possibility of non-perf NMI sources when applying
  the mitigation.

This patch series is based off of the perf/core branch of tip:
  https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git perf/core

  Commit c978b9460fe1 ("Merge tag 'perf-core-for-mingo-5.1-20190225' of git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux into perf/core")