arch/powerpc/firmware-assisted-dump.rst

14 - Fadump uses the same firmware interfaces and memory reservation model
16 - Unlike phyp dump, FADump exports the memory dump through /proc/vmcore
21 - Unlike phyp dump, FADump allows user to release all the memory reserved
35 -  Once the dump is copied out, the memory that held the dump
44 -  The first kernel registers the sections of memory with the
46    These registered sections of memory are reserved by the first
50    low memory regions (boot memory) from source to destination area.
54          The term 'boot memory' means size of the low memory chunk
56          booted with restricted memory. By default, the boot memory
58          Alternatively, user can also specify boot memory size
61          boot memory size is not sufficient for second kernel to
65          ignored as FADump uses a predefined offset to reserve memory
66          for boot memory dump preservation in case of a crash.
68 -  After the low memory (boot memory) area has been saved, the
77    the early boot OS will reserve rest of the memory above
78    boot memory size effectively booting with restricted memory
81    of the dump memory area.
84    of memory, which holds the previous crashed kernel dump in ELF
90    memory back to general use, except the memory required for
108 preserve previously crash'ed kernel's memory for the subsequent
114    CONFIG_OPAL_CORE=y, OPAL memory at the time of crash is also
116    helpful in debugging OPAL crashes with GDB. The kernel memory
129 then everything but boot memory size of RAM is reserved during
134 memory is held.
136 If there is no waiting dump data, then only the memory required to
137 hold CPU state, HPTE region, boot memory dump, and FADump header is
138 usually reserved at an offset greater than boot memory size (see Fig. 1).
141 memory content in addition to CPU state and HPTE region, in the case
144 Since this reserved memory area is used only after the system crash,
145 there is no point in blocking this significant chunk of memory from
147 Contiguous Memory Allocator (CMA) for memory reservation if CMA is
148 configured for kernel. With CMA reservation this memory will be
151 kernel memory and most of the user space memory except the user pages
154   o Memory Reservation during first kernel
156   Low memory                                                  Top of memory
157   0    boot memory size   |<------ Reserved dump area ----->|     |
167       Boot memory content gets transferred         |      |
183   o Memory Reservation during second kernel after crash
185   Low memory                                              Top of memory
186   0      boot memory size                                      |
214         Note: Memory from 0 to the boot memory size is used by second kernel
235    By default, FADump reserved memory will be initialized as CMA area.
239    to specify size of the memory to reserve for boot memory dump
244         use 'crashkernel=' to specify size of the memory to reserve
245         for boot memory dump preservation.
246      2. If firmware-assisted dump fails to reserve memory then it
249      3. if user wants to capture all of user space memory and ok with
250         reserved memory not available to production system, then
258 the control files and debugfs file to display memory reserved region.
286    This is used to display the memory reserved by FADump for saving the
291     second kernel. This is used to release the reserved memory
293     reserved memory echo 1 to it::
298     file will change to reflect the new memory reservations.
301     enhanced to use this interface to release the memory reserved for
310     active during capture kernel. This is used to release the memory
312     release this memory, echo '1' to it:
332     This file shows the reserved memory regions if FADump is
367    accurate boot memory size that is required for a kernel to
368    boot successfully when booted with restricted memory.