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Commit fbcafdae authored by Hari Bathini's avatar Hari Bathini Committed by Michael Ellerman
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powerpc/fadump: Update documentation about OPAL platform support 

With FADump support now available on both pseries and OPAL platforms,
update FADump documentation with these details.
Signed-off-by: default avatarHari Bathini <hbathini@linux.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/156821361692.5656.11377757995827253404.stgit@hbathini.in.ibm.com
parent a4e2e2ca
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Documentation/powerpc/firmware-assisted-dump.rst
View file @ fbcafdae
......@@ -46,10 +46,9 @@ as follows:
These registered sections of memory are reserved by the first
kernel during early boot.
- When a system crashes, the Power firmware will save
the low memory (boot memory of size larger of 5% of system RAM
or 256MB) of RAM to the previous registered region. It will
also save system registers, and hardware PTE's.
- When system crashes, the Power firmware will copy the registered
low memory regions (boot memory) from source to destination area.
It will also save hardware PTE's.
NOTE:
The term 'boot memory' means size of the low memory chunk
......@@ -61,9 +60,9 @@ as follows:
the default calculated size. Use this option if default
boot memory size is not sufficient for second kernel to
boot successfully. For syntax of crashkernel= parameter,
refer to Documentation/admin-guide/kdump/kdump.rst. If any offset is
provided in crashkernel= parameter, it will be ignored
as FADump uses a predefined offset to reserve memory
refer to Documentation/admin-guide/kdump/kdump.rst. If any
offset is provided in crashkernel= parameter, it will be
ignored as FADump uses a predefined offset to reserve memory
for boot memory dump preservation in case of a crash.
- After the low memory (boot memory) area has been saved, the
......@@ -71,8 +70,9 @@ as follows:
*not* clear the RAM. It will then launch the bootloader, as
normal.
- The freshly booted kernel will notice that there is a new
node (ibm,dump-kernel) in the device tree, indicating that
- The freshly booted kernel will notice that there is a new node
(rtas/ibm,kernel-dump on pSeries or ibm,opal/dump/mpipl-boot
on OPAL platform) in the device tree, indicating that
there is crash data available from a previous boot. During
the early boot OS will reserve rest of the memory above
boot memory size effectively booting with restricted memory
......@@ -95,8 +95,11 @@ as follows:
# echo 1 > /sys/kernel/fadump_release_mem
Please note that the firmware-assisted dump feature
is only available on Power6 and above systems with recent
firmware versions.
is only available on POWER6 and above systems on pSeries
(PowerVM) platform and POWER9 and above systems with OP940
or later firmware versions on PowerNV (OPAL) platform.
Note that, OPAL firmware exports ibm,opal/dump node when
FADump is supported on PowerNV platform.
Implementation details:
-----------------------
......@@ -111,57 +114,76 @@ that are run. If there is dump data, then the
/sys/kernel/fadump_release_mem file is created, and the reserved
memory is held.
If there is no waiting dump data, then only the memory required
to hold CPU state, HPTE region, boot memory dump and elfcore
header, is usually reserved at an offset greater than boot memory
size (see Fig. 1). This area is *not* released: this region will
be kept permanently reserved, so that it can act as a receptacle
for a copy of the boot memory content in addition to CPU state
and HPTE region, in the case a crash does occur. Since this reserved
memory area is used only after the system crash, there is no point in
blocking this significant chunk of memory from production kernel.
Hence, the implementation uses the Linux kernel's Contiguous Memory
Allocator (CMA) for memory reservation if CMA is configured for kernel.
With CMA reservation this memory will be available for applications to
use it, while kernel is prevented from using it. With this FADump will
still be able to capture all of the kernel memory and most of the user
space memory except the user pages that were present in CMA region::
If there is no waiting dump data, then only the memory required to
hold CPU state, HPTE region, boot memory dump, FADump header and
elfcore header, is usually reserved at an offset greater than boot
memory size (see Fig. 1). This area is *not* released: this region
will be kept permanently reserved, so that it can act as a receptacle
for a copy of the boot memory content in addition to CPU state and
HPTE region, in the case a crash does occur.
Since this reserved memory area is used only after the system crash,
there is no point in blocking this significant chunk of memory from
production kernel. Hence, the implementation uses the Linux kernel's
Contiguous Memory Allocator (CMA) for memory reservation if CMA is
configured for kernel. With CMA reservation this memory will be
available for applications to use it, while kernel is prevented from
using it. With this FADump will still be able to capture all of the
kernel memory and most of the user space memory except the user pages
that were present in CMA region::
o Memory Reservation during first kernel
Low memory Top of memory
0 boot memory size |<--Reserved dump area --->| |
| | | (Permanent Reservation) | |
V V | | V
+-----------+----------/ /---+---+----+--------+---+----+------+
| | |CPU|HPTE| DUMP |HDR|ELF | |
+-----------+----------/ /---+---+----+--------+---+----+------+
| ^ ^
| | |
\ / |
----------------------------------- FADump Header
Boot memory content gets transferred (meta area)
to reserved area by firmware at the
time of crash
Low memory Top of memory
0 boot memory size |<--- Reserved dump area --->| |
| | | Permanent Reservation | |
V V | | V
+-----------+-----/ /---+---+----+-------+-----+-----+----+--+
| | |///|////| DUMP | HDR | ELF |////| |
+-----------+-----/ /---+---+----+-------+-----+-----+----+--+
| ^ ^ ^ ^ ^
| | | | | |
\ CPU HPTE / | |
------------------------------ | |
Boot memory content gets transferred | |
to reserved area by firmware at the | |
time of crash. | |
FADump Header |
(meta area) |
|
|
Metadata: This area holds a metadata struture whose
address is registered with f/w and retrieved in the
second kernel after crash, on platforms that support
tags (OPAL). Having such structure with info needed
to process the crashdump eases dump capture process.
Fig. 1
o Memory Reservation during second kernel after crash
Low memory Top of memory
0 boot memory size |
| |<----------- Crash preserved area --------------->|
V V |<-- Reserved dump area -->| V
+-----------+----------/ /---+---+----+--------+---+----+------+
| | |CPU|HPTE| DUMP |HDR|ELF | |
+-----------+----------/ /---+---+----+--------+---+----+------+
| |
V V
Used by second /proc/vmcore
Low memory Top of memory
0 boot memory size |
| |<------------ Crash preserved area ------------>|
V V |<--- Reserved dump area --->| |
+-----------+-----/ /---+---+----+-------+-----+-----+----+--+
| | |///|////| DUMP | HDR | ELF |////| |
+-----------+-----/ /---+---+----+-------+-----+-----+----+--+
| |
V V
Used by second /proc/vmcore
kernel to boot
+---+
|///| -> Regions (CPU, HPTE & Metadata) marked like this in the above
+---+ figures are not always present. For example, OPAL platform
does not have CPU & HPTE regions while Metadata region is
not supported on pSeries currently.
Fig. 2
Currently the dump will be copied from /proc/vmcore to a new file upon
user intervention. The dump data available through /proc/vmcore will be
in ELF format. Hence the existing kdump infrastructure (kdump scripts)
......
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