Update docs with PMU security information
This patch adds information on the PMU configuration registers
and security considerations related to the PMU.
Signed-off-by: Petre-Ionut Tudor <petre-ionut.tudor@arm.com>
Change-Id: I36b15060b9830a77d3f47f293c0a6dafa3c581fb
diff --git a/docs/perf/performance-monitoring-unit.rst b/docs/perf/performance-monitoring-unit.rst
new file mode 100644
index 0000000..5dd1af5
--- /dev/null
+++ b/docs/perf/performance-monitoring-unit.rst
@@ -0,0 +1,158 @@
+Performance Monitoring Unit
+===========================
+
+The Performance Monitoring Unit (PMU) allows recording of architectural and
+microarchitectural events for profiling purposes.
+
+This document gives an overview of the PMU counter configuration to assist with
+implementation and to complement the PMU security guidelines given in the
+:ref:`Secure Development Guidelines` document.
+
+.. note::
+ This section applies to Armv8-A implementations which have version 3
+ of the Performance Monitors Extension (PMUv3).
+
+PMU Counters
+------------
+
+The PMU makes 32 counters available at all privilege levels:
+
+- 31 programmable event counters: ``PMEVCNTR<n>``, where ``n`` is ``0`` to
+ ``30``.
+- A dedicated cycle counter: ``PMCCNTR``.
+
+Architectural mappings
+~~~~~~~~~~~~~~~~~~~~~~
+
++--------------+---------+----------------------------+
+| Counters | State | System Register Name |
++==============+=========+============================+
+| | AArch64 | ``PMEVCNTR<n>_EL0[63*:0]`` |
+| Programmable +---------+----------------------------+
+| | AArch32 | ``PMEVCNTR<n>[31:0]`` |
++--------------+---------+----------------------------+
+| | AArch64 | ``PMCCNTR_EL0[63:0]`` |
+| Cycle +---------+----------------------------+
+| | AArch32 | ``PMCCNTR[63:0]`` |
++--------------+---------+----------------------------+
+
+.. note::
+ Bits [63:32] are only available if ARMv8.5-PMU is implemented. Refer to the
+ `Arm ARM`_ for a detailed description of ARMv8.5-PMU features.
+
+Configuring the PMU for counting events
+---------------------------------------
+
+Each programmable counter has an associated register, ``PMEVTYPER<n>`` which
+configures it. The cycle counter has the ``PMCCFILTR_EL0`` register, which has
+an identical function and bit field layout as ``PMEVTYPER<n>``. In addition,
+the counters are enabled (permitted to increment) via the ``PMCNTENSET`` and
+``PMCR`` registers. These can be accessed at all privilege levels.
+
+Architectural mappings
+~~~~~~~~~~~~~~~~~~~~~~
+
++-----------------------------+------------------------+
+| AArch64 | AArch32 |
++=============================+========================+
+| ``PMEVTYPER<n>_EL0[63*:0]`` | ``PMEVTYPER<n>[31:0]`` |
++-----------------------------+------------------------+
+| ``PMCCFILTR_EL0[63*:0]`` | ``PMCCFILTR[31:0]`` |
++-----------------------------+------------------------+
+| ``PMCNTENSET_EL0[63*:0]`` | ``PMCNTENSET[31:0]`` |
++-----------------------------+------------------------+
+| ``PMCR_EL0[63*:0]`` | ``PMCR[31:0]`` |
++-----------------------------+------------------------+
+
+.. note::
+ Bits [63:32] are reserved.
+
+Relevant register fields
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+For ``PMEVTYPER<n>_EL0``/``PMEVTYPER<n>`` and ``PMCCFILTR_EL0/PMCCFILTR``, the
+most important fields are:
+
+- ``P``:
+
+ - Bit 31.
+ - If set to ``0``, will increment the associated ``PMEVCNTR<n>`` at EL1.
+
+- ``NSK``:
+
+ - Bit 29.
+ - If equal to the ``P`` bit it enables the associated ``PMEVCNTR<n>`` at
+ Non-secure EL1.
+ - Reserved if EL3 not implemented.
+
+- ``NSH``:
+
+ - Bit 27.
+ - If set to ``1``, will increment the associated ``PMEVCNTR<n>`` at EL2.
+ - Reserved if EL2 not implemented.
+
+- ``SH``:
+
+ - Bit 24.
+ - If different to the ``NSH`` bit it enables the associated ``PMEVCNTR<n>``
+ at Secure EL2.
+ - Reserved if Secure EL2 not implemented.
+
+- ``M``:
+
+ - Bit 26.
+ - If equal to the ``P`` bit it enables the associated ``PMEVCNTR<n>`` at
+ EL3.
+
+- ``evtCount[15:10]``:
+
+ - Extension to ``evtCount[9:0]``. Reserved unless ARMv8.1-PMU implemented.
+
+- ``evtCount[9:0]``:
+
+ - The event number that the associated ``PMEVCNTR<n>`` will count.
+
+For ``PMCNTENSET_EL0``/``PMCNTENSET``, the most important fields are:
+
+- ``P[30:0]``:
+
+ - Setting bit ``P[n]`` to ``1`` enables counter ``PMEVCNTR<n>``.
+ - The effects of ``PMEVTYPER<n>`` are applied on top of this.
+ In other words, the counter will not increment at any privilege level or
+ security state unless it is enabled here.
+
+- ``C``:
+
+ - Bit 31.
+ - If set to ``1`` enables the cycle counter ``PMCCNTR``.
+
+For ``PMCR``/``PMCR_EL0``, the most important fields are:
+
+- ``DP``:
+
+ - Bit 5.
+ - If set to ``1`` it disables the cycle counter ``PMCCNTR`` where event
+ counting (by ``PMEVCNTR<n>``) is prohibited (e.g. EL2 and the Secure
+ world).
+ - If set to ``0``, ``PMCCNTR`` will not be affected by this bit and
+ therefore will be able to count where the programmable counters are
+ prohibited.
+
+- ``E``:
+
+ - Bit 0.
+ - Enables/disables counting altogether.
+ - The effects of ``PMCNTENSET`` and ``PMCR.DP`` are applied on top of this.
+ In other words, if this bit is ``0`` then no counters will increment
+ regardless of how the other PMU system registers or bit fields are
+ configured.
+
+.. rubric:: References
+
+- `Arm ARM`_
+
+--------------
+
+*Copyright (c) 2019-2020, Arm Limited and Contributors. All rights reserved.*
+
+.. _Arm ARM: https://developer.arm.com/docs/ddi0487/latest