perf: arm_pmuv3: Add support for the Branch Record Buffer Extension (BRBE)

The ARMv9.2 architecture introduces the optional Branch Record Buffer
Extension (BRBE), which records information about branches as they are
executed into set of branch record registers. BRBE is similar to x86's
Last Branch Record (LBR) and PowerPC's Branch History Rolling Buffer
(BHRB).

BRBE supports filtering by exception level and can filter just the
source or target address if excluded to avoid leaking privileged
addresses. The h/w filter would be sufficient except when there are
multiple events with disjoint filtering requirements. In this case, BRBE
is configured with a union of all the events' desired branches, and then
the recorded branches are filtered based on each event's filter. For
example, with one event capturing kernel events and another event
capturing user events, BRBE will be configured to capture both kernel
and user branches. When handling event overflow, the branch records have
to be filtered by software to only include kernel or user branch
addresses for that event. In contrast, x86 simply configures LBR using
the last installed event which seems broken.

The event and branch exception level filtering are separately
controlled. On x86, it is possible to request filtering which is
disjoint (e.g. kernel only event with user only branches). It is also
possible on x86 to configure branch filter such that no branches are
ever recorded (e.g. -j save_type). For BRBE, events with mismatched
exception level filtering or a configuration that will result in no
samples are rejected. This can be relaxed in the future if such a need
arises.

The handling of KVM guests is similar to the above. On x86, branch
recording is always disabled when a guest is running. However,
requesting branch recording in guests is allowed. The guest events are
recorded, but the resulting branches are all from the host. For BRBE,
branch recording is similarly disabled when guest is running. In
addition, events with branch recording and "exclude_host" set are
rejected. Requiring "exclude_guest" to be set did not work. The default
for the perf tool does set "exclude_guest" if no exception level
options are specified. However, specifying kernel or user defaults to
including both host and guest. In this case, only host branches are
recorded.

BRBE can support some additional exception, FIQ, and debug branch
types, but they are not supported currently. There's no control in the
perf ABI to enable/disable these branch types, so they could only be
enabled for the 'any' filter which might be undesired or unexpected.
The other architectures don't have any support similar events (at least
with perf). These can be added in the future if there is demand by
adding additional specific filter types.

BRBE records are invalidated whenever events are reconfigured, a new
task is scheduled in, or after recording is paused (and the records
have been recorded for the event). The architecture allows branch
records to be invalidated by the PE under implementation defined
conditions. It is expected that these conditions are rare.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Co-developed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Co-developed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
---
v19:
- Drop saving of branch records when task scheduled out. (Mark)
- Got rid of added armpmu ops. All BRBE support contained within pmuv3
  code.
- Dropped armpmu.num_branch_records as reg_brbidr has same info.
- Make sched_task() callback actually get called. Enabling requires a
  call to perf_sched_cb_inc().
- Fix freeze on overflow for VHE
- The cycle counter doesn't freeze BRBE on overflow, so avoid assigning
  it when BRBE is enabled.
- Drop all the Arm specific exception branches. Not a clear need for
  them.
- Simplify enable/disable to avoid RMW and document ISBs needed
- Fix handling of branch 'cycles' reading. CC field is
  mantissa/exponent, not an integer.
- Save BRBFCR and BRBCR settings in event->hw.branch_reg.config and
  event->hw.extra_reg.config to avoid recalculating the register value
  each time the event is installed.
- Rework s/w filtering to better match h/w filtering
- Reject events with disjoint event filter and branch filter
- Reject events if exclude_host is set

v18: https://lore.kernel.org/all/20240613061731.3109448-6-anshuman.khandual@arm.com/