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-rw-r--r--Documentation/arm64/cpu-feature-registers.rst17
-rw-r--r--Documentation/arm64/elf_hwcaps.rst8
-rw-r--r--Documentation/arm64/perf.rst78
-rw-r--r--Documentation/arm64/pointer-authentication.rst9
-rw-r--r--Documentation/arm64/tagged-address-abi.rst2
5 files changed, 107 insertions, 7 deletions
diff --git a/Documentation/arm64/cpu-feature-registers.rst b/Documentation/arm64/cpu-feature-registers.rst
index 9f9b8fd06089..749ae970c319 100644
--- a/Documentation/arm64/cpu-feature-registers.rst
+++ b/Documentation/arm64/cpu-feature-registers.rst
@@ -275,6 +275,23 @@ infrastructure:
| SVEVer | [3-0] | y |
+------------------------------+---------+---------+
+ 8) ID_AA64MMFR1_EL1 - Memory model feature register 1
+
+ +------------------------------+---------+---------+
+ | Name | bits | visible |
+ +------------------------------+---------+---------+
+ | AFP | [47-44] | y |
+ +------------------------------+---------+---------+
+
+ 9) ID_AA64ISAR2_EL1 - Instruction set attribute register 2
+
+ +------------------------------+---------+---------+
+ | Name | bits | visible |
+ +------------------------------+---------+---------+
+ | RPRES | [7-4] | y |
+ +------------------------------+---------+---------+
+
+
Appendix I: Example
-------------------
diff --git a/Documentation/arm64/elf_hwcaps.rst b/Documentation/arm64/elf_hwcaps.rst
index af106af8e1c0..b72ff17d600a 100644
--- a/Documentation/arm64/elf_hwcaps.rst
+++ b/Documentation/arm64/elf_hwcaps.rst
@@ -251,6 +251,14 @@ HWCAP2_ECV
Functionality implied by ID_AA64MMFR0_EL1.ECV == 0b0001.
+HWCAP2_AFP
+
+ Functionality implied by ID_AA64MFR1_EL1.AFP == 0b0001.
+
+HWCAP2_RPRES
+
+ Functionality implied by ID_AA64ISAR2_EL1.RPRES == 0b0001.
+
4. Unused AT_HWCAP bits
-----------------------
diff --git a/Documentation/arm64/perf.rst b/Documentation/arm64/perf.rst
index b567f177d385..1f87b57c2332 100644
--- a/Documentation/arm64/perf.rst
+++ b/Documentation/arm64/perf.rst
@@ -2,7 +2,10 @@
.. _perf_index:
-=====================
+====
+Perf
+====
+
Perf Event Attributes
=====================
@@ -88,3 +91,76 @@ exclude_host. However when using !exclude_hv there is a small blackout
window at the guest entry/exit where host events are not captured.
On VHE systems there are no blackout windows.
+
+Perf Userspace PMU Hardware Counter Access
+==========================================
+
+Overview
+--------
+The perf userspace tool relies on the PMU to monitor events. It offers an
+abstraction layer over the hardware counters since the underlying
+implementation is cpu-dependent.
+Arm64 allows userspace tools to have access to the registers storing the
+hardware counters' values directly.
+
+This targets specifically self-monitoring tasks in order to reduce the overhead
+by directly accessing the registers without having to go through the kernel.
+
+How-to
+------
+The focus is set on the armv8 PMUv3 which makes sure that the access to the pmu
+registers is enabled and that the userspace has access to the relevant
+information in order to use them.
+
+In order to have access to the hardware counters, the global sysctl
+kernel/perf_user_access must first be enabled:
+
+.. code-block:: sh
+
+ echo 1 > /proc/sys/kernel/perf_user_access
+
+It is necessary to open the event using the perf tool interface with config1:1
+attr bit set: the sys_perf_event_open syscall returns a fd which can
+subsequently be used with the mmap syscall in order to retrieve a page of memory
+containing information about the event. The PMU driver uses this page to expose
+to the user the hardware counter's index and other necessary data. Using this
+index enables the user to access the PMU registers using the `mrs` instruction.
+Access to the PMU registers is only valid while the sequence lock is unchanged.
+In particular, the PMSELR_EL0 register is zeroed each time the sequence lock is
+changed.
+
+The userspace access is supported in libperf using the perf_evsel__mmap()
+and perf_evsel__read() functions. See `tools/lib/perf/tests/test-evsel.c`_ for
+an example.
+
+About heterogeneous systems
+---------------------------
+On heterogeneous systems such as big.LITTLE, userspace PMU counter access can
+only be enabled when the tasks are pinned to a homogeneous subset of cores and
+the corresponding PMU instance is opened by specifying the 'type' attribute.
+The use of generic event types is not supported in this case.
+
+Have a look at `tools/perf/arch/arm64/tests/user-events.c`_ for an example. It
+can be run using the perf tool to check that the access to the registers works
+correctly from userspace:
+
+.. code-block:: sh
+
+ perf test -v user
+
+About chained events and counter sizes
+--------------------------------------
+The user can request either a 32-bit (config1:0 == 0) or 64-bit (config1:0 == 1)
+counter along with userspace access. The sys_perf_event_open syscall will fail
+if a 64-bit counter is requested and the hardware doesn't support 64-bit
+counters. Chained events are not supported in conjunction with userspace counter
+access. If a 32-bit counter is requested on hardware with 64-bit counters, then
+userspace must treat the upper 32-bits read from the counter as UNKNOWN. The
+'pmc_width' field in the user page will indicate the valid width of the counter
+and should be used to mask the upper bits as needed.
+
+.. Links
+.. _tools/perf/arch/arm64/tests/user-events.c:
+ https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/arch/arm64/tests/user-events.c
+.. _tools/lib/perf/tests/test-evsel.c:
+ https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/lib/perf/tests/test-evsel.c
diff --git a/Documentation/arm64/pointer-authentication.rst b/Documentation/arm64/pointer-authentication.rst
index f127666ea3a8..e5dad2e40aa8 100644
--- a/Documentation/arm64/pointer-authentication.rst
+++ b/Documentation/arm64/pointer-authentication.rst
@@ -53,11 +53,10 @@ The number of bits that the PAC occupies in a pointer is 55 minus the
virtual address size configured by the kernel. For example, with a
virtual address size of 48, the PAC is 7 bits wide.
-Recent versions of GCC can compile code with APIAKey-based return
-address protection when passed the -msign-return-address option. This
-uses instructions in the HINT space (unless -march=armv8.3-a or higher
-is also passed), and such code can run on systems without the pointer
-authentication extension.
+When ARM64_PTR_AUTH_KERNEL is selected, the kernel will be compiled
+with HINT space pointer authentication instructions protecting
+function returns. Kernels built with this option will work on hardware
+with or without pointer authentication support.
In addition to exec(), keys can also be reinitialized to random values
using the PR_PAC_RESET_KEYS prctl. A bitmask of PR_PAC_APIAKEY,
diff --git a/Documentation/arm64/tagged-address-abi.rst b/Documentation/arm64/tagged-address-abi.rst
index 0c9120ec58ae..540a1d4fc6c9 100644
--- a/Documentation/arm64/tagged-address-abi.rst
+++ b/Documentation/arm64/tagged-address-abi.rst
@@ -49,7 +49,7 @@ how the user addresses are used by the kernel:
- ``brk()``, ``mmap()`` and the ``new_address`` argument to
``mremap()`` as these have the potential to alias with existing
- user addresses.
+ user addresses.
NOTE: This behaviour changed in v5.6 and so some earlier kernels may
incorrectly accept valid tagged pointers for the ``brk()``,