arch/powerpc/firmware-assisted-dump.rst

22   for dump, with a single operation of echo 1 > /sys/kernel/fadump_release_mem.
23 - Once enabled through kernel boot parameter, FADump can be
24   started/stopped through /sys/kernel/fadump_registered interface (see
32    with a fresh copy of the kernel.  In particular,
36    is immediately available to the running kernel. And therefore,
44 -  The first kernel registers the sections of memory with the
47    kernel during early boot.
55          that is required for a kernel to boot successfully when
61          boot memory size is not sufficient for second kernel to
73 -  The freshly booted kernel will notice that there is a new node
74    (rtas/ibm,kernel-dump on pSeries or ibm,opal/dump/mpipl-boot
79    size. This will make sure that this kernel (also, referred
80    to as second kernel or capture kernel) will not touch any
84    of memory, which holds the previous crashed kernel dump in ELF
89    '1' to /sys/kernel/fadump_release_mem to release the reserved
95      # echo 1 > /sys/kernel/fadump_release_mem
105 kernel (referred to as petitboot kernel) before booting into the
106 capture kernel. This kernel would have minimal kernel and/or
107 userspace support to process crash data. Such kernel needs to
108 preserve previously crash'ed kernel's memory for the subsequent
109 capture kernel boot to process this crash data. Kernel config
110 option CONFIG_PRESERVE_FA_DUMP has to be enabled on such kernel
113 -- On OPAL based machines (PowerNV), if the kernel is build with
116    helpful in debugging OPAL crashes with GDB. The kernel memory
123 -- Support for Additional Kernel Arguments in Fadump
124    Fadump has a feature that allows passing additional kernel arguments
125    to the fadump kernel. This feature was primarily designed to disable
126    kernel functionalities that are not required for the fadump kernel
129   Command to Add Additional Kernel Parameters to Fadump:
131   # echo "nr_cpus=16" > /sys/kernel/fadump/bootargs_append
138   # cat /sys/kernel/fadump/bootargs_append
140 Note: Additional kernel arguments for fadump with HASH MMU is only
142       size is less than 768 MB, the kernel does not export the
143       /sys/kernel/fadump/bootargs_append sysfs node.
155 /sys/kernel/fadump_release_mem file is created, and the reserved
168 production kernel. Hence, the implementation uses the Linux kernel's
170 configured for kernel. With CMA reservation this memory will be
171 available for applications to use it, while kernel is prevented from
173 kernel memory and most of the user space memory except the user pages
176   o Memory Reservation during first kernel
198                       second kernel after crash, on platforms that support
205   o Memory Reservation during second kernel after crash
233         |ELF| -> elfcorehdr, it is created in second kernel after crash.
236         Note: Memory from 0 to the boot memory size is used by second kernel
255 1. Set config option CONFIG_FA_DUMP=y and build kernel.
256 2. Boot into linux kernel with 'fadump=on' kernel cmdline option.
258    Alternatively, user can boot linux kernel with 'fadump=nocma' to
260 3. Optionally, user can also set 'crashkernel=' kernel cmdline
270         option is set at kernel cmdline.
273         'fadump=nocma' kernel parameter can be used to fallback to
282 Here is the list of files under kernel sysfs:
284  /sys/kernel/fadump_enabled
291     FADump is enabled in the kernel and act accordingly.
293  /sys/kernel/fadump_registered
300     To register FADump echo 1 > /sys/kernel/fadump_registered and
301     echo 0 > /sys/kernel/fadump_registered for un-register and stop the
306  /sys/kernel/fadump/mem_reserved
311  /sys/kernel/fadump_release_mem
313     second kernel. This is used to release the reserved memory
317 	echo 1  > /sys/kernel/fadump_release_mem
319     After echo 1, the content of the /sys/kernel/debug/powerpc/fadump_region
326 Note: /sys/kernel/fadump_release_opalcore sysfs has moved to
332     active during capture kernel. This is used to release the memory
333     used by the kernel to export /sys/firmware/opal/mpipl/core file. To
343 | /sys/kernel/fadump_enabled       | /sys/kernel/fadump/enabled     |
345 | /sys/kernel/fadump_registered    | /sys/kernel/fadump/registered  |
347 | /sys/kernel/fadump_release_mem   | /sys/kernel/fadump/release_mem |
351 (Assuming debugfs is mounted on /sys/kernel/debug directory.)
353  /sys/kernel/debug/powerpc/fadump_region
360     and for kernel DUMP region is:
365     Contents when FADump is registered during first kernel::
367       # cat /sys/kernel/debug/powerpc/fadump_region
372     Contents when FADump is active during second kernel::
374       # cat /sys/kernel/debug/powerpc/fadump_region
389    accurate boot memory size that is required for a kernel to