[PATCHv4 0/2] tracing/rwmmio/arm64: Add support to trace register reads/writes

[Sai Prakash Ranjan]

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_read: gic_peek_irq+0xd0/0xd8 readl addr=0xffff800010040104
rwmmio_write: gic_poke_irq+0xe4/0xf0 writel addr=0xffff800010040184 
rwmmio_read: gic_do_wait_for_rwp+0x54/0x90 readl addr=0xffff800010040000
rwmmio_write: gic_set_affinity+0x1bc/0x1e8 writeq addr=0xffff800010046130

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@xxxxxxxxxxxxxx/
[2] https://lore.kernel.org/lkml/1604631386-178312-1-git-send-email-psodagud@xxxxxxxxxxxxxx/

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):
  tracing: Add register read/write tracing support

Sai Prakash Ranjan (1):
  arm64/io: Add a header for mmio access instrumentation

 arch/arm64/include/asm/io.h       | 25 ++++-------
 arch/arm64/kvm/hyp/nvhe/Makefile  |  2 +-
 include/linux/mmio-instrumented.h | 70 +++++++++++++++++++++++++++++++
 include/trace/events/rwmmio.h     | 59 ++++++++++++++++++++++++++
 kernel/trace/Kconfig              |  7 ++++
 kernel/trace/Makefile             |  1 +
 kernel/trace/trace_readwrite.c    | 29 +++++++++++++
 7 files changed, 176 insertions(+), 17 deletions(-)
 create mode 100644 include/linux/mmio-instrumented.h
 create mode 100644 include/trace/events/rwmmio.h
 create mode 100644 kernel/trace/trace_readwrite.c

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2.33.1