linux-kernel - Re: [PATCHv9 0/5] lib/rwmmio/arm64: Add support to trace register reads/writes

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Message-ID: <ae3db4cc-67ab-e968-44da-0d88f1b5092b@quicinc.com>
Date:   Tue, 1 Feb 2022 00:26:18 +0530
From:   Sai Prakash Ranjan <quic_saipraka@...cinc.com>
To:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Arnd Bergmann <arnd@...db.de>, Marc Zyngier <maz@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
CC:     gregkh <gregkh@...uxfoundation.org>, <quic_psodagud@...cinc.com>,
        "Trilok Soni" <quic_tsoni@...cinc.com>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCHv9 0/5] lib/rwmmio/arm64: Add support to trace register
 reads/writes

Hi Arnd, Steve

On 1/24/2022 12:03 PM, Sai Prakash Ranjan wrote:
> 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 previous 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 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 (4):
>    arm64: io: Use asm-generic high level MMIO accessors
>    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 +++----
>   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 +++++++++++++++
>   11 files changed, 265 insertions(+), 54 deletions(-)
>   create mode 100644 include/trace/events/rwmmio.h
>   create mode 100644 lib/trace_readwrite.c
>
>
> base-commit: bd8d9cef2a7932e688ca267ea1adf5ea6557c777

Any comments on this version?

Thanks,
Sai