arch/powerpc/firmware-assisted-dump.rst

2 Firmware-Assisted Dump
7 The goal of firmware-assisted dump is to enable the dump of
12 - Firmware-Assisted Dump (FADump) infrastructure is intended to replace
13   the existing phyp assisted dump.
15   as phyp assisted dump.
16 - Unlike phyp dump, FADump exports the memory dump through /proc/vmcore
18   kdump infrastructure for dump capture and filtering.
19 - Unlike phyp dump, userspace tool does not need to refer any sysfs
21 - Unlike phyp dump, FADump allows user to release all the memory reserved
22   for dump, with a single operation of echo 1 > /sys/kernel/fadump_release_mem.
29 dump offers several strong, practical advantages:
35 -  Once the dump is copied out, the memory that held the dump
45    Power firmware for dump preservation during OS initialization.
66          for boot memory dump preservation in case of a crash.
74    (rtas/ibm,kernel-dump on pSeries or ibm,opal/dump/mpipl-boot
81    of the dump memory area.
84    of memory, which holds the previous crashed kernel dump in ELF
88 -  Once the userspace tool is done saving dump, it will echo
91    next firmware-assisted dump registration.
97 Please note that the firmware-assisted dump feature
101 Note that, OPAL firmware exports ibm,opal/dump node when
127    and to reduce its memory footprint while collecting the dump.
150 we check to see if an active dump is waiting for us. If yes
153 collecting the dump from user land scripts (e.g. kdump scripts)
154 that are run. If there is dump data, then the
158 If there is no waiting dump data, then only the memory required to
159 hold CPU state, HPTE region, boot memory dump, and FADump header is
179   0    boot memory size   |<------ Reserved dump area ----->|     |
183   |           |           |///|////|    DUMP   |  HDR  |////|     |
200                       to process the crashdump eases dump capture process.
210   V           V           |<--- Reserved dump area --->|       |
212   |    |ELF|  |           |///|////|  DUMP | HDR |/////|       |
241 Currently the dump will be copied from /proc/vmcore to a new file upon
242 user intervention. The dump data available through /proc/vmcore will be
244 to save the dump works fine with minor modifications. KDump scripts on
246 user intervention in saving the dump) when FADump is used, instead of
247 KDump, as dump mechanism.
249 The tools to examine the dump will be same as the ones
252 How to enable firmware-assisted dump (FADump):
261    to specify size of the memory to reserve for boot memory dump
267         for boot memory dump preservation.
268      2. If firmware-assisted dump fails to reserve memory then it
279 Firmware-assisted dump feature uses sysfs file system to hold
309    crash dump.
314     region that are held for saving crash dump. To release the
324     dump and continue without 2nd reboot.
358       <region>: [<start>-<end>] <reserved-size> bytes, Dumped: <dump-size>
360     and for kernel DUMP region is:
362     DUMP: Src: <src-addr>, Dest: <dest-addr>, Size: <size>, Dumped: # bytes
370       DUMP: [0x0000006fff1020-0x0000007fff101f] 0x10000000 bytes, Dumped: 0x0
377       DUMP: [0x0000006fff1020-0x0000007fff101f] 0x10000000 bytes, Dumped: 0x10000000
396 assisted dump by Linas Vepstas and Manish Ahuja.