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Message-ID: <20240916103437.226816-9-lcherian@marvell.com>
Date: Mon, 16 Sep 2024 16:04:37 +0530
From: Linu Cherian <lcherian@...vell.com>
To: <suzuki.poulose@....com>, <mike.leach@...aro.org>, <james.clark@....com>
CC: <linux-arm-kernel@...ts.infradead.org>, <coresight@...ts.linaro.org>,
<linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>,
<robh@...nel.org>, <krzk+dt@...nel.org>, <conor+dt@...nel.org>,
<corbet@....net>, <devicetree@...r.kernel.org>, <sgoutham@...vell.com>,
<gcherian@...vell.com>, Linu Cherian <lcherian@...vell.com>
Subject: [PATCH v10 8/8] Documentation: coresight: Panic support
Add documentation on using coresight during panic
and watchdog.
Signed-off-by: Linu Cherian <lcherian@...vell.com>
---
Changelog from v9:
This patch has been newly introduced.
Documentation/trace/coresight/panic.rst | 356 ++++++++++++++++++++++++
1 file changed, 356 insertions(+)
create mode 100644 Documentation/trace/coresight/panic.rst
diff --git a/Documentation/trace/coresight/panic.rst b/Documentation/trace/coresight/panic.rst
new file mode 100644
index 000000000000..3b53d91cace8
--- /dev/null
+++ b/Documentation/trace/coresight/panic.rst
@@ -0,0 +1,356 @@
+===================================================
+Using Coresight for Kernel panic and Watchdog reset
+===================================================
+
+Introduction
+------------
+This documentation is about using Linux coresight trace support to
+debug kernel panic and watchdog reset scenarios.
+
+Coresight trace during 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.
+
+
+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::
+
+ Trigger on panic
+ Comparator --->External out --->CTI -->External In---->ETR/ETF stop
+
+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.
+
+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 a special device file /dev/crash_tmc_xxx.
+This device file is created only when there is a valid crashdata available.
+
+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 sinks should 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 during 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.
+
+Sample commands for testing a Kernel panic case with ETR sink
+-------------------------------------------------------------
+
+1. Boot Linux kernel with "crash_kexec_post_notifiers" added to the kernel
+ bootargs. This is mandatory if the user would like to read the tracedata
+ from the crashdump kernel.
+
+2. Enable the preloaded ETM configuration
+
+ #echo 1 > /sys/kernel/config/cs-syscfg/configurations/panicstop/enable
+
+3. 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.
+
+4. Choose reserved buffer mode for ETR buffer
+ #echo "resrv" > /sys/bus/coresight/devices/tmc_etr0/buf_mode_preferred
+
+5. Enable stop on flush trigger configuration
+ #echo 1 > /sys/bus/coresight/devices/tmc_etr0/stop_on_flush
+
+6. Start Coresight tracing on cores 1 and 2 using sysfs interface
+
+7. Run some application on core 1
+ #taskset -c 1 dd if=/dev/urandom of=/dev/null &
+
+8. Invoke kernel panic on core 2
+ #echo 1 > /proc/sys/kernel/panic
+ #taskset -c 2 echo c > /proc/sysrq-trigger
+
+9. From rebooted kernel or crashdump kernel, read crashdata
+
+ #dd if=/dev/crash_tmc_etr0 of=/trace/cstrace.bin
+
+10. Run opencsd decoder tools/scripts to generate the instruction trace.
+
+Sample instruction trace dump
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Core1 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
+
+
+Core 2 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 149.046243445 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
+------------------
+
+Starting perf session
+~~~~~~~~~~~~~~~~~~~~~
+ETF:
+perf record -e cs_etm/panicstop,@tmc_etf1/ -C 1
+perf record -e cs_etm/panicstop,@tmc_etf2/ -C 2
+
+ETR:
+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.
--
2.34.1
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