[PATCH v8 0/7] Coresight for Kernel panic and watchdog reset

From: Linu Cherian
Date: Fri May 31 2024 - 00:28:25 EST

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This patch series is rebased on v6.9.0.

Changelog from v7:
* Fixed breakage on perf test -vvvv "arm coresight".
No issues seen with and without "resrv" buffer mode
* Moved the crashdev registration into a seperate function.
* Removed redundant variable in tmc_etr_setup_crashdata_buf
* Avoided a redundant memcpy in tmc_panic_sync_etf.
* Tested kernel panic with trace session started uisng perf.
Please see the title "Perf based testing" below for details.
For this, stop_on_flush sysfs attribute is taken into
consideration while starting perf sessions as well.

Changelog from v6:
* Added special device files for reading crashdata, so that
read_prevboot mode flag is removed.
* Added new sysfs TMC device attribute, stop_on_flush.
Stop on flush trigger event is disabled by default.
User need to explicitly enable this from sysfs for panic stop
to work.
* Address parameter for panicstop ETM configuration is
chosen as kernel "panic" address by default.
* Added missing tmc_wait_for_tmcready during panic handling
* Few other misc code rearrangements.

Changelog from v5:
* Fixed issues reported by CONFIG_DEBUG_ATOMIC_SLEEP
* Fixed a memory leak while reading data from /dev/tmc_etrx in
READ_PREVBOOT mode
* Tested reading trace data from crashdump kernel

Changelog from v4:
* Device tree binding
- Description is made more explicit on the usage of reserved memory
region
- Mismatch in memory region names in dts binding and driver fixed
- Removed "mem" suffix from the memory region names
* Rename "struct tmc_register_snapshot" -> "struct tmc_crash_metadata",
since it contains more than register snapshot.
Related variables are named accordingly.
* Rename struct tmc_drvdata members
resrv_buf -> crash_tbuf
metadata -> crash_mdata
* Size field in metadata refers to RSZ register and hence indicates the
size in 32 bit words. ETR metadata follows this convention, the same
has been extended to ETF metadata as well.
* Added crc32 for more robust metadata and tracedata validation.
* Added/modified dev_dbg messages during metadata validation
* Fixed a typo in patch 5 commit description

Changelog from v3:
* Converted the Coresight ETM driver change to a named configuration.
RFC tag has been removed with this change.
* Fixed yaml issues reported by "make dt_binding_check"
* Added names for reserved memory regions 0 and 1
* Added prevalidation checks for metadata processing
* Fixed a regression introduced in RFC v3
- TMC Status register was getting saved wrongly
* Reverted memremap attribute changes from _WB to _WC to match
with the dma map attributes
* Introduced reserved buffer mode specific .sync op.
This fixes a possible crash when reserved buffer mode was used in
normal trace capture, due to unwanted dma maintenance operations.

v7 is posted here:
https://lore.kernel.org/lkml/20240307033625.325058-1-lcherian@xxxxxxxxxxx/

Using Coresight for Kernel panic and Watchdog reset
===================================================
This patch series is about extending Linux coresight driver support to
address kernel panic and watchdog reset scenarios. This would help
coresight users to debug kernel panic and watchdog reset using
coresight trace data.

Coresight trace capture: Kernel panic
-------------------------------------
>From the coresight driver point of view, addressing the kernel panic
situation has four main requirements.

a. Support for allocation of trace buffer pages from reserved memory area.
Platform can advertise this using a new device tree property added to
relevant coresight nodes.

b. Support for stopping coresight blocks at the time of panic

c. Saving required metadata in the specified format

d. Support for reading trace data captured at the time of panic

Allocation of trace buffer pages from reserved RAM
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A new optional device tree property "memory-region" is added to the
ETR/ETF device nodes, that would give the base address and size of trace
buffer.

Static allocation of trace buffers would ensure that both IOMMU enabled
and disabled cases are handled. Also, platforms that support persistent
RAM will allow users to read trace data in the subsequent boot without
booting the crashdump kernel.

Note:
For ETR sink devices, this reserved region will be used for both trace
capture and trace data retrieval.
For ETF sink devices, internal SRAM would be used for trace capture,
and they would be synced to reserved region for retrieval.

Note: Patches 1 & 2 adds support for this.

Disabling coresight blocks at the time of panic
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In order to avoid the situation of losing relevant trace data after a
kernel panic, it would be desirable to stop the coresight blocks at the
time of panic.

This can be achieved by configuring the comparator, CTI and sink
devices as below,

Comparator(triggers on kernel panic) --->External out --->CTI --
|
ETR/ETF stop <------External In <--------------
Note:

* Patch 6 provides the necessary ETR configuration.
* Patch 7 provides the necessary ETM configuration.

Saving metadata at the time of kernel panic
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Coresight metadata involves all additional data that are required for a
successful trace decode in addition to the trace data. This involves
ETR/ETF, ETE register snapshot etc.

A new optional device property "memory-region" is added to
the ETR/ETF/ETE device nodes for this.

Note: Patches 3 & 4 adds support for this.

Reading trace data captured at the time of panic
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Trace data captured at the time of panic, can be read from rebooted kernel
or from crashdump kernel using the below mentioned interface.

Note: Patch 5 adds support for this.

Steps for reading trace data captured in previous boot
++++++++++++++++++++++++++++++++++++++++++++++++++++++
1. cd /sys/bus/coresight/devices/tmc_etrXX/

2. Dump trace buffer crashdata to a file,

#dd if=/dev/crash_tmc_etrXX of=~/cstrace.bin

General flow of trace capture and decode incase of kernel panic
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1. Enable source and sink on all the cores using the sysfs interface.
ETR sink will have trace buffers allocated from reserved memory,
by selecting "resrv" buffer mode from sysfs.

2. Run relevant tests.

3. On a kernel panic, all coresight blocks are disabled, necessary
metadata is synced by kernel panic handler.

System would eventually reboot or boot a crashdump kernel.

4. For platforms that supports crashdump kernel, raw trace data can be
dumped using the coresight sysfs interface from the crashdump kernel
itself. Persistent RAM is not a requirement in this case.

5. For platforms that supports persistent RAM, trace data can be dumped
using the coresight sysfs interface in the subsequent Linux boot.
Crashdump kernel is not a requirement in this case. Persistent RAM
ensures that trace data is intact across reboot.

Coresight trace capture: Watchdog reset
---------------------------------------
The main difference between addressing the watchdog reset and kernel panic
case are below,

a. Saving coresight metadata need to be taken care by the
SCP(system control processor) firmware in the specified format,
instead of kernel.

b. Reserved memory region given by firmware for trace buffer and metadata
has to be in persistent RAM.
Note: This is a requirement for watchdog reset case but optional
in kernel panic case.

Watchdog reset can be supported only on platforms that meet the above
two requirements.

Testing Kernel panic on Linux 6.8
---------------------------------
1. Enable the preloaded ETM configuration

#echo 1 > /sys/kernel/config/cs-syscfg/configurations/panicstop/enable

2. Configure CTI using sysfs interface

#./cti_setup.sh

#cat cti_setup.sh

cd /sys/bus/coresight/devices/

ap_cti_config () {
#ETM trig out[0] trigger to Channel 0
echo 0 4 > channels/trigin_attach
}

etf_cti_config () {
#ETF Flush in trigger from Channel 0
echo 0 1 > channels/trigout_attach
echo 1 > channels/trig_filter_enable
}

etr_cti_config () {
#ETR Flush in from Channel 0
echo 0 1 > channels/trigout_attach
echo 1 > channels/trig_filter_enable
}

ctidevs=`find . -name "cti*"`

for i in $ctidevs
do
cd $i

connection=`find . -name "ete*"`
if [ ! -z "$connection" ]
then
echo "AP CTI config for $i"
ap_cti_config
fi

connection=`find . -name "tmc_etf*"`
if [ ! -z "$connection" ]
then
echo "ETF CTI config for $i"
etf_cti_config
fi

connection=`find . -name "tmc_etr*"`
if [ ! -z "$connection" ]
then
echo "ETR CTI config for $i"
etr_cti_config
fi

cd ..
done

Note: CTI connections are SOC specific and hence the above script is
added just for reference.

3. Choose reserved buffer mode for ETR buffer
#echo "resrv" > /sys/bus/coresight/devices/tmc_etr0/buf_mode_preferred

4. Enable stop on flush trigger configuration
#echo 1 > /sys/bus/coresight/devices/tmc_etr0/stop_on_flush

4. Start Coresight tracing on cores 1 and 2 using sysfs interface

5. Run some application on core 1
#taskset -c 1 dd if=/dev/urandom of=/dev/null &

6. Invoke kernel panic on core 2
#echo 1 > /proc/sys/kernel/panic
#taskset -c 2 echo c > /proc/sysrq-trigger

7. From rebooted kernel or crashdump kernel, read crashdata

Note: For crashdump kernel option, please make sure "crash_kexec_post_notifiers" is
added to the kernel bootargs.

#dd if=/dev/crash_tmc_etr0 of=/trace/cstrace.bin

8. Run opencsd decoder tools/scripts to generate the instruction trace.

Sample Core 1 instruction trace dump:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A etm4_enable_hw: ffff800008ae1dd4
CONTEXT EL2 etm4_enable_hw: ffff800008ae1dd4
I etm4_enable_hw: ffff800008ae1dd4:
d503201f nop
I etm4_enable_hw: ffff800008ae1dd8:
d503201f nop
I etm4_enable_hw: ffff800008ae1ddc:
d503201f nop
I etm4_enable_hw: ffff800008ae1de0:
d503201f nop
I etm4_enable_hw: ffff800008ae1de4:
d503201f nop
I etm4_enable_hw: ffff800008ae1de8:
d503233f paciasp
I etm4_enable_hw: ffff800008ae1dec:
a9be7bfd stp x29, x30, [sp, #-32]!
I etm4_enable_hw: ffff800008ae1df0:
910003fd mov x29, sp
I etm4_enable_hw: ffff800008ae1df4:
a90153f3 stp x19, x20, [sp, #16]
I etm4_enable_hw: ffff800008ae1df8:
2a0003f4 mov w20, w0
I etm4_enable_hw: ffff800008ae1dfc:
900085b3 adrp x19, ffff800009b95000 <reserved_mem+0xc48>
I etm4_enable_hw: ffff800008ae1e00:
910f4273 add x19, x19, #0x3d0
I etm4_enable_hw: ffff800008ae1e04:
f8747a60 ldr x0, [x19, x20, lsl #3]
E etm4_enable_hw: ffff800008ae1e08:
b4000140 cbz x0, ffff800008ae1e30 <etm4_starting_cpu+0x50>
I 149.039572921 etm4_enable_hw: ffff800008ae1e30:
a94153f3 ldp x19, x20, [sp, #16]
I 149.039572921 etm4_enable_hw: ffff800008ae1e34:
52800000 mov w0, #0x0 // #0
I 149.039572921 etm4_enable_hw: ffff800008ae1e38:
a8c27bfd ldp x29, x30, [sp], #32

..snip

149.052324811 chacha_block_generic: ffff800008642d80:
9100a3e0 add x0,
I 149.052324811 chacha_block_generic: ffff800008642d84:
b86178a2 ldr w2, [x5, x1, lsl #2]
I 149.052324811 chacha_block_generic: ffff800008642d88:
8b010803 add x3, x0, x1, lsl #2
I 149.052324811 chacha_block_generic: ffff800008642d8c:
b85fc063 ldur w3, [x3, #-4]
I 149.052324811 chacha_block_generic: ffff800008642d90:
0b030042 add w2, w2, w3
I 149.052324811 chacha_block_generic: ffff800008642d94:
b8217882 str w2, [x4, x1, lsl #2]
I 149.052324811 chacha_block_generic: ffff800008642d98:
91000421 add x1, x1, #0x1
I 149.052324811 chacha_block_generic: ffff800008642d9c:
f100443f cmp x1, #0x11

Sample Core 2 instruction trace dump(kernel panic triggered core):
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A etm4_enable_hw: ffff800008ae1dd4
CONTEXT EL2 etm4_enable_hw: ffff800008ae1dd4
I etm4_enable_hw: ffff800008ae1dd4:
d503201f nop
I etm4_enable_hw: ffff800008ae1dd8:
d503201f nop
I etm4_enable_hw: ffff800008ae1ddc:
d503201f nop
I etm4_enable_hw: ffff800008ae1de0:
d503201f nop
I etm4_enable_hw: ffff800008ae1de4:
d503201f nop
I etm4_enable_hw: ffff800008ae1de8:
d503233f paciasp
I etm4_enable_hw: ffff800008ae1dec:
a9be7bfd stp x29, x30, [sp, #-32]!
I etm4_enable_hw: ffff800008ae1df0:
910003fd mov x29, sp
I etm4_enable_hw: ffff800008ae1df4:
a90153f3 stp x19, x20, [sp, #16]
I etm4_enable_hw: ffff800008ae1df8:
2a0003f4 mov w20, w0
I etm4_enable_hw: ffff800008ae1dfc:
900085b3 adrp x19, ffff800009b95000 <reserved_mem+0xc48>
I etm4_enable_hw: ffff800008ae1e00:
910f4273 add x19, x19, #0x3d0
I etm4_enable_hw: ffff800008ae1e04:
f8747a60 ldr x0, [x19, x20, lsl #3]
E etm4_enable_hw: ffff800008ae1e08:
b4000140 cbz x0, ffff800008ae1e30 <etm4_starting_cpu+0x50>
I 149.046243445 etm4_enable_hw: ffff800008ae1e30:
a94153f3 ldp x19, x20, [sp, #16]
I 149.046243445 etm4_enable_hw: ffff800008ae1e34:
52800000 mov w0, #0x0 // #0
I 149.046243445 etm4_enable_hw: ffff800008ae1e38:
a8c27bfd ldp x29, x30, [sp], #32
I 149.046243445 etm4_enable_hw: ffff800008ae1e3c:
d50323bf autiasp
E 149.046243445 etm4_enable_hw: ffff800008ae1e40:
d65f03c0 ret
A ete_sysreg_write: ffff800008adfa18

..snip

I 149.05422547 panic: ffff800008096300:
a90363f7 stp x23, x24, [sp, #48]
I 149.05422547 panic: ffff800008096304:
6b00003f cmp w1, w0
I 149.05422547 panic: ffff800008096308:
3a411804 ccmn w0, #0x1, #0x4, ne // ne = any
N 149.05422547 panic: ffff80000809630c:
540001e0 b.eq ffff800008096348 <panic+0xe0> // b.none
I 149.05422547 panic: ffff800008096310:
f90023f9 str x25, [sp, #64]
E 149.05422547 panic: ffff800008096314:
97fe44ef bl ffff8000080276d0 <panic_smp_self_stop>
A panic: ffff80000809634c
I 149.05422547 panic: ffff80000809634c:
910102d5 add x21, x22, #0x40
I 149.05422547 panic: ffff800008096350:
52800020 mov w0, #0x1 // #1
E 149.05422547 panic: ffff800008096354:
94166b8b bl ffff800008631180 <bust_spinlocks>
N 149.054225518 bust_spinlocks: ffff800008631180:
340000c0 cbz w0, ffff800008631198 <bust_spinlocks+0x18>
I 149.054225518 bust_spinlocks: ffff800008631184:
f000a321 adrp x1, ffff800009a98000 <pbufs.0+0xbb8>
I 149.054225518 bust_spinlocks: ffff800008631188:
b9405c20 ldr w0, [x1, #92]
I 149.054225518 bust_spinlocks: ffff80000863118c:
11000400 add w0, w0, #0x1
I 149.054225518 bust_spinlocks: ffff800008631190:
b9005c20 str w0, [x1, #92]
E 149.054225518 bust_spinlocks: ffff800008631194:
d65f03c0 ret
A panic: ffff800008096358

Perf based testing
------------------
Kernel panic during perf trace sessions has been tested with this series.

Starting perf session
~~~~~~~~~~~~~~~~~~~~~
ETF:
/tools/perf/perf record -e cs_etm/panicstop,@tmc_etf1/ -C 1
/tools/perf/perf record -e cs_etm/panicstop,@tmc_etf2/ -C 2

ETR:
/tools/perf/perf record -e cs_etm/panicstop,@tmc_etr0/ -C 1,2

Reading trace data after panic
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Same sysfs based method explained above can be used to retrieve and
decode the trace data after the reboot on kernel panic.

Future Improvements
-------------------
* Explore changing CTI sysfs script to system configuration manager profile

Linu Cherian (7):
dt-bindings: arm: coresight-tmc: Add "memory-region" property
coresight: tmc-etr: Add support to use reserved trace memory
coresight: core: Add provision for panic callbacks
coresight: tmc: Enable panic sync handling
coresight: tmc: Add support for reading crash data
coresight: tmc: Stop trace capture on FlIn
coresight: config: Add preloaded configuration

.../bindings/arm/arm,coresight-tmc.yaml | 26 ++
drivers/hwtracing/coresight/Makefile | 2 +-
.../coresight/coresight-cfg-preload.c | 2 +
.../coresight/coresight-cfg-preload.h | 2 +
.../hwtracing/coresight/coresight-cfg-pstop.c | 83 +++++
drivers/hwtracing/coresight/coresight-core.c | 37 ++
.../coresight/coresight-etm4x-core.c | 1 +
.../hwtracing/coresight/coresight-tmc-core.c | 251 +++++++++++++-
.../hwtracing/coresight/coresight-tmc-etf.c | 163 ++++++++-
.../hwtracing/coresight/coresight-tmc-etr.c | 319 +++++++++++++++++-
drivers/hwtracing/coresight/coresight-tmc.h | 83 +++++
include/linux/coresight.h | 25 ++
12 files changed, 977 insertions(+), 17 deletions(-)
create mode 100644 drivers/hwtracing/coresight/coresight-cfg-pstop.c

--
2.34.1

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