[PATCH V2 0/6] powerpc/perf: Add HTM PMU driver and perf AUX support

[Athira Rajeev <atrajeev@linux.ibm.com>]

Overview:
The Hardware Trace Macro (HTM) on POWER systems provides hardware-level
bus-trace data for a specific node/chip/core target within a logical
partition.  It is accessed via the H_HTM hypervisor call and traces
continuously at node, chip, or core scope independent of task scheduling.

This series adds a new "htm" PMU driver under arch/powerpc/perf/ that
exposes HTM trace collection via the standard perf interface using the
perf AUX buffer infrastructure, together with ABI and RST documentation.

Patch overview:
Patch 1 introduces the core HTM PMU driver (htm-perf.c).  The event
configuration encodes the trace target as a 28-bit value in
perf_event_attr.config:

  bits  0-3:  htm_type         (HTM_CORE=2, HTM_NEST=1)
  bits  4-11: nodeindex
  bits 12-19: nodalchipindex
  bits 20-27: coreindexonchip

The PMU lifecycle maps to H_HTM_OP_CONFIGURE/DECONFIGURE at add/del time
and H_HTM_OP_START/STOP at start/stop time.  Context-switch callbacks
(PERF_EF_RELOAD / PERF_EF_UPDATE) are intentionally ignored because HTM
traces the hardware scope, not individual tasks.  Tracing state is kept
in event->pmu_private (HTM_TRACING_ACTIVE / HTM_TRACING_INACTIVE) as the
authoritative source, with event->hw.state kept in sync as a hint for the
perf core.

Patch 2 adds duplicate-reservation protection.  When 'perf record -a' is
used, perf opens system-wide events on all CPUs in parallel.  Without
driver-side tracking, concurrent opens for the same HTM target (node,
chip, core, type) can race and issue duplicate H_HTM_OP_CONFIGURE flows.
A global reserved-targets list is added; htm_event_init() rejects any
open that matches an already-reserved tuple, while different targets can
still be opened simultaneously on different CPUs.

Patch 3 adds AUX ring-buffer support so that high-volume trace data can
be streamed into a perf AUX buffer.  The driver opts into
PERF_PMU_CAP_AUX_NO_SG | PERF_PMU_CAP_AUX_PREFER_LARGE to request
physically contiguous allocations, which H_HTM_OP_DUMP_DATA requires.
A page-by-page physical-continuity scan is performed before each dump to
detect and bound any fragmentation gaps, preventing silent memory
corruption.  event->count is set to 1 when data is present and 0 when
the stream is exhausted; the perf tool uses this as a drain signal to
decide whether another read pass is needed before closing the event.

Patch 4 adds system memory configuration capture.  After writing trace
data to the AUX buffer, htm_event_read() calls H_HTM_OP_DUMP_SYSMEM_CONF
and emits the returned physical-to-logical address mapping records as
PERF_SAMPLE_RAW data.  Keeping trace data in the AUX stream and memory
configuration in raw samples allows each to be decoded independently in
userspace.

Patch 5 adds ABI documentation for the sysfs entries under
/sys/bus/event_source/devices/htm/, covering the format attribute
(config bit layout) and the events attribute group.

Patch 6 extends Documentation/arch/powerpc/htm.rst with a new section
on the perf interface: event syntax, required options, the two output
files (htm.bin.nX.pX.cX and translation.nX.pX.cX), and how to pass
them to htmdecode for trace decoding.

Usage example:
Collect HTM trace data from two simultaneous chip targets:

  # perf record -m,256                                          \
      -e htm/nodalchipindex=2,nodeindex=0,htm_type=1,cpu=8/    \
      -e htm/nodalchipindex=1,nodeindex=0,htm_type=1,cpu=9/    \
      -a -- sleep 10

  # perf report

Output files written by perf report:

  htm.bin.n0.p2.c0       raw HTM bus-trace, chip 2
  htm.bin.n0.p1.c0       raw HTM bus-trace, chip 1
  translation.n0.p2.c0   memory config records, chip 2
  translation.n0.p1.c0   memory config records, chip 1

The htm.bin.* files can then be decoded with htmdecoder to produce
trace output.

Testing:
Tested on POWER10 with two simultaneous HTM targets.  Both htm.bin.*
and translation.* files are produced correctly.

  # perf record -C 9 -m,256 \
      -e htm/nodalchipindex=2,nodeindex=0,htm_type=1/ sleep 3
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 256.277 MB perf.data ]

Athira Rajeev (6):
  powerpc/perf: Add HTM PMU driver to expose Hardware Trace Macro data
  powerpc/perf: Reject duplicate HTM target reservations
  powerpc/perf: Add AUX buffer management to capture HTM trace data
  powerpc/perf: Capture the HTM memory configuration as part of perf
    data
  docs: ABI: sysfs-bus-event_source-devices-htm: Document sysfs event
    format entries for htm pmu
  powerpc/perf/htm: Add documentation for Hardware Trace Macro PMU

 .../sysfs-bus-event_source-devices-htm        |  21 +
 Documentation/arch/powerpc/htm.rst            | 137 +++-
 arch/powerpc/perf/Makefile                    |   2 +-
 arch/powerpc/perf/htm-perf.c                  | 749 ++++++++++++++++++
 4 files changed, 905 insertions(+), 4 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-bus-event_source-devices-htm
 create mode 100644 arch/powerpc/perf/htm-perf.c

-- 
2.43.0