[PATCHv11 0/6] lib/rwmmio/arm64: Add support to trace register reads/writes

Sai Prakash Ranjan
2022-04-28T03:31:28Z

Generic MMIO read/write i.e., __raw_{read,write}{b,l,w,q} accessors
are typically used to read/write from/to memory mapped registers
and can cause hangs or some undefined behaviour in following cases,

* If the access to the register space is unclocked, for example: if
there is an access to multimedia(MM) block registers without MM
clocks.

* If the register space is protected and not set to be accessible from
non-secure world, for example: only EL3 (EL: Exception level) access
is allowed and any EL2/EL1 access is forbidden.

* If xPU(memory/register protection units) is controlling access to
certain memory/register space for specific clients.

and more...

Such cases usually results in instant reboot/SErrors/NOC or interconnect
hangs and tracing these register accesses can be very helpful to debug
such issues during initial development stages and also in later stages.

So use ftrace trace events to log such MMIO register accesses which
provides rich feature set such as early enablement of trace events,
filtering capability, dumping ftrace logs on console and many more.

Sample output:

rwmmio_write: __qcom_geni_serial_console_write+0x160/0x1e0 width=32 val=0xa0d5d addr=0xfffffbfffdbff700
rwmmio_post_write: __qcom_geni_serial_console_write+0x160/0x1e0 width=32 val=0xa0d5d addr=0xfffffbfffdbff700
rwmmio_read: qcom_geni_serial_poll_bit+0x94/0x138 width=32 addr=0xfffffbfffdbff610
rwmmio_post_read: qcom_geni_serial_poll_bit+0x94/0x138 width=32 val=0x0 addr=0xfffffbfffdbff610

This series is a follow-up for the series [1] and a recent series [2] making use
of both.

[1] https://lore.kernel.org/lkml/cover.1536430404.git.saiprakash.ranjan@codeaurora.org/
[2] https://lore.kernel.org/lkml/1604631386-178312-1-git-send-email-psodagud@codeaurora.org/

Note in v4 version, Arnd suggested to benchmark and compare size with callback
based implementation, please see [3] for more details on that with brief comparison below.

**Inline version with CONFIG_FTRACE=y and CONFIG_TRACE_MMIO_ACCESS=y**
$ size vmlinux
text data bss dec hex filename
23884219 14284468 532568 38701255 24e88c7 vmlinux

**Callback version with CONFIG_FTRACE=y and CONFIG_TRACE_MMIO_ACCESS=y**
$ size vmlinux
text data bss dec hex filename
24108179 14279596 532568 38920343 251e097 vmlinux

$ ./scripts/bloat-o-meter inline-vmlinux callback-vmlinux
add/remove: 8/3 grow/shrink: 4889/89 up/down: 242244/-11564 (230680)
Total: Before=25812612, After=26043292, chg +0.89%

[3] https://lore.kernel.org/lkml/466449a1-36da-aaa9-7e4f-477f36b52c9e@quicinc.com/

Changes in v11:
* Use unsigned long for caller ip and current ip addr (Steven Rostedt).
* Include review tags from Arnd.

Changes in v10:
* Use GENMASK(31, 0) for -Woverflow warning in irqchip tegra driver (Marc).
* Convert ETM4x ARM64 driver to use asm-generic IO memory barriers (Catalin).
* Collect ack from Catalin for arm64 change.

Changes in v9:
* Use TRACE_EVENT_CLASS for rwmmio_write and post_write (Steven Rostedt).

Changes in v8:
* Fix build error reported by kernel test robot.

Changes in v7:
* Use lib/ instead of kernel/trace/ based on review comment by Steven Rostedt.

Changes in v6:
* Implemented suggestions by Arnd Bergmann:
- Use arch independent IO barriers in arm64/asm
- Add ARCH_HAVE_TRACE_MMIO_ACCESS
- Add post read and post write logging support
- Remove tracepoint_active check
* Fix build error reported by kernel test robot.

Changes in v5:
* Move arm64 to use asm-generic provided high level MMIO accessors (Arnd).
* Add inline logging for MMIO relaxed and non-relaxed accessors.
* Move nVHE KVM comment to makefile (Marc).
* Fix overflow warning due to switch to inline accessors instead of macro.
* Modify trace event field to include caller and parent details for more detailed logs.

Changes in v4:
* Drop dynamic debug based filter support since that will be developed later with
the help from Steven (Ftrace maintainer).
* Drop value passed to writel as it is causing hangs when tracing is enabled.
* Code cleanup for trace event as suggested by Steven for earlier version.
* Fixed some build errors reported by 0-day bot.

Changes in v3:
* Create a generic mmio header for instrumented version (Earlier suggested in [1]
by Will Deacon and recently [2] by Greg to have a generic version first).
* Add dynamic debug support to filter out traces which can be very useful for targeted
debugging specific to subsystems or drivers.
* Few modifications to the rwmmio trace event fields to include the mmio width and print
addresses in hex.
* Rewrote commit msg to explain some more about usecases.

Prasad Sodagudi (1):
lib: Add register read/write tracing support

Sai Prakash Ranjan (5):
arm64: io: Use asm-generic high level MMIO accessors
coresight: etm4x: Use asm-generic IO memory barriers
irqchip/tegra: Fix overflow implicit truncation warnings
drm/meson: Fix overflow implicit truncation warnings
asm-generic/io: Add logging support for MMIO accessors

arch/Kconfig | 3 +
arch/arm64/Kconfig | 1 +
arch/arm64/include/asm/io.h | 41 ++------
arch/arm64/kvm/hyp/nvhe/Makefile | 7 +-
drivers/gpu/drm/meson/meson_viu.c | 22 ++---
.../coresight/coresight-etm4x-core.c | 8 +-
drivers/hwtracing/coresight/coresight-etm4x.h | 8 +-
drivers/irqchip/irq-tegra.c | 10 +-
include/asm-generic/io.h | 82 +++++++++++++++-
include/trace/events/rwmmio.h | 97 +++++++++++++++++++
lib/Kconfig | 7 ++
lib/Makefile | 2 +
lib/trace_readwrite.c | 47 +++++++++
13 files changed, 273 insertions(+), 62 deletions(-)
create mode 100644 include/trace/events/rwmmio.h
create mode 100644 lib/trace_readwrite.c

base-commit: 53ab78cd6d5aba25575a7cfb95729336ba9497d8
--
2.33.1