On 2024-10-03 at 19:13:10, Suzuki K Poulose (suzuki.poulose@xxxxxxx) wrote:
> Hi Linu
>
> On 16/09/2024 11:34, Linu Cherian wrote:
> > Add documentation on using coresight during panic
> > and watchdog.
>
> Thank you so much for the documentation, this will be quite useful !
>
> Some minor comments below.
>
> >
> > Signed-off-by: Linu Cherian <lcherian@xxxxxxxxxxx>
> > ---
> > 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
>
> ETR/ETF => CoreSight TMC
Ack.
>
> > +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.
>
> s/ETE/ETB ?
Ack.
>
> > +
> > +A new optional device property "memory-region" is added to
> > +the ETR/ETF/ETE device nodes for this.
>
> same here ^^
Ack.
>
>
> > +
> > +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 $i
> > +
> > + connection=`find . -name "ete*"`
>
> minor nit: this could be ete or etm
Ack.
>
> > + if [ ! -z "$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.
>
>
Linu Cherian
