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powerpc/fadump: use FADump instead of fadump for how it is pronounced 

fadump is pronounced f-a-dump. Update documentation accordingly. Also,
update how fadump_region contents look like with recent changes.

Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/156821339317.5656.15852294223821732082.stgit@hbathini.in.ibm.com
This commit is contained in:
Hari Bathini 2019-09-11 20:19:58 +05:30 committed by Michael Ellerman
parent f35120115b
commit 1679b96e69
1 changed files with 30 additions and 25 deletions
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55
Documentation/powerpc/firmware-assisted-dump.rst
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@ -9,18 +9,18 @@ a crashed system, and to do so from a fully-reset system, and
to minimize the total elapsed time until the system is back to minimize the total elapsed time until the system is back
in production use. in production use.
- Firmware assisted dump (fadump) infrastructure is intended to replace - Firmware-Assisted Dump (FADump) infrastructure is intended to replace
the existing phyp assisted dump. the existing phyp assisted dump.
- Fadump uses the same firmware interfaces and memory reservation model - Fadump uses the same firmware interfaces and memory reservation model
as phyp assisted dump. as phyp assisted dump.
- Unlike phyp dump, fadump exports the memory dump through /proc/vmcore - Unlike phyp dump, FADump exports the memory dump through /proc/vmcore
in the ELF format in the same way as kdump. This helps us reuse the in the ELF format in the same way as kdump. This helps us reuse the
kdump infrastructure for dump capture and filtering. kdump infrastructure for dump capture and filtering.
- Unlike phyp dump, userspace tool does not need to refer any sysfs - Unlike phyp dump, userspace tool does not need to refer any sysfs
interface while reading /proc/vmcore. interface while reading /proc/vmcore.
- Unlike phyp dump, fadump allows user to release all the memory reserved - Unlike phyp dump, FADump allows user to release all the memory reserved
for dump, with a single operation of echo 1 > /sys/kernel/fadump_release_mem. for dump, with a single operation of echo 1 > /sys/kernel/fadump_release_mem.
- Once enabled through kernel boot parameter, fadump can be - Once enabled through kernel boot parameter, FADump can be
started/stopped through /sys/kernel/fadump_registered interface (see started/stopped through /sys/kernel/fadump_registered interface (see
sysfs files section below) and can be easily integrated with kdump sysfs files section below) and can be easily integrated with kdump
service start/stop init scripts. service start/stop init scripts.
@ -34,7 +34,7 @@ dump offers several strong, practical advantages:
in a clean, consistent state. in a clean, consistent state.
- Once the dump is copied out, the memory that held the dump - Once the dump is copied out, the memory that held the dump
is immediately available to the running kernel. And therefore, is immediately available to the running kernel. And therefore,
unlike kdump, fadump doesn't need a 2nd reboot to get back unlike kdump, FADump doesn't need a 2nd reboot to get back
the system to the production configuration. the system to the production configuration.
The above can only be accomplished by coordination with, The above can only be accomplished by coordination with,
@ -63,7 +63,7 @@ as follows:
boot successfully. For syntax of crashkernel= parameter, boot successfully. For syntax of crashkernel= parameter,
refer to Documentation/admin-guide/kdump/kdump.rst. If any offset is refer to Documentation/admin-guide/kdump/kdump.rst. If any offset is
provided in crashkernel= parameter, it will be ignored provided in crashkernel= parameter, it will be ignored
as fadump uses a predefined offset to reserve memory as FADump uses a predefined offset to reserve memory
for boot memory dump preservation in case of a crash. for boot memory dump preservation in case of a crash.
- After the low memory (boot memory) area has been saved, the - After the low memory (boot memory) area has been saved, the
@ -123,7 +123,7 @@ blocking this significant chunk of memory from production kernel.
Hence, the implementation uses the Linux kernel's Contiguous Memory Hence, the implementation uses the Linux kernel's Contiguous Memory
Allocator (CMA) for memory reservation if CMA is configured for kernel. Allocator (CMA) for memory reservation if CMA is configured for kernel.
With CMA reservation this memory will be available for applications to With CMA reservation this memory will be available for applications to
use it, while kernel is prevented from using it. With this fadump will 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 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:: space memory except the user pages that were present in CMA region::
@ -173,14 +173,14 @@ KDump, as dump mechanism.
The tools to examine the dump will be same as the ones The tools to examine the dump will be same as the ones
used for kdump. used for kdump.
How to enable firmware-assisted dump (fadump): How to enable firmware-assisted dump (FADump):
---------------------------------------------- ----------------------------------------------
1. Set config option CONFIG_FA_DUMP=y and build kernel. 1. Set config option CONFIG_FA_DUMP=y and build kernel.
2. Boot into linux kernel with 'fadump=on' kernel cmdline option. 2. Boot into linux kernel with 'fadump=on' kernel cmdline option.
By default, fadump reserved memory will be initialized as CMA area. By default, FADump reserved memory will be initialized as CMA area.
Alternatively, user can boot linux kernel with 'fadump=nocma' to Alternatively, user can boot linux kernel with 'fadump=nocma' to
prevent fadump to use CMA. prevent FADump to use CMA.
3. Optionally, user can also set 'crashkernel=' kernel cmdline 3. Optionally, user can also set 'crashkernel=' kernel cmdline
to specify size of the memory to reserve for boot memory dump to specify size of the memory to reserve for boot memory dump
preservation. preservation.
@ -206,29 +206,29 @@ the control files and debugfs file to display memory reserved region.
Here is the list of files under kernel sysfs: Here is the list of files under kernel sysfs:
/sys/kernel/fadump_enabled /sys/kernel/fadump_enabled
This is used to display the fadump status. This is used to display the FADump status.
- 0 = fadump is disabled - 0 = FADump is disabled
- 1 = fadump is enabled - 1 = FADump is enabled
This interface can be used by kdump init scripts to identify if This interface can be used by kdump init scripts to identify if
fadump is enabled in the kernel and act accordingly. FADump is enabled in the kernel and act accordingly.
/sys/kernel/fadump_registered /sys/kernel/fadump_registered
This is used to display the fadump registration status as well This is used to display the FADump registration status as well
as to control (start/stop) the fadump registration. as to control (start/stop) the FADump registration.
- 0 = fadump is not registered. - 0 = FADump is not registered.
- 1 = fadump is registered and ready to handle system crash. - 1 = FADump is registered and ready to handle system crash.
To register fadump echo 1 > /sys/kernel/fadump_registered and To register FADump echo 1 > /sys/kernel/fadump_registered and
echo 0 > /sys/kernel/fadump_registered for un-register and stop the echo 0 > /sys/kernel/fadump_registered for un-register and stop the
fadump. Once the fadump is un-registered, the system crash will not FADump. Once the FADump is un-registered, the system crash will not
be handled and vmcore will not be captured. This interface can be be handled and vmcore will not be captured. This interface can be
easily integrated with kdump service start/stop. easily integrated with kdump service start/stop.
/sys/kernel/fadump_release_mem /sys/kernel/fadump_release_mem
This file is available only when fadump is active during This file is available only when FADump is active during
second kernel. This is used to release the reserved memory second kernel. This is used to release the reserved memory
region that are held for saving crash dump. To release the region that are held for saving crash dump. To release the
reserved memory echo 1 to it:: reserved memory echo 1 to it::
@ -246,21 +246,25 @@ Here is the list of files under powerpc debugfs:
(Assuming debugfs is mounted on /sys/kernel/debug directory.) (Assuming debugfs is mounted on /sys/kernel/debug directory.)
/sys/kernel/debug/powerpc/fadump_region /sys/kernel/debug/powerpc/fadump_region
This file shows the reserved memory regions if fadump is This file shows the reserved memory regions if FADump is
enabled otherwise this file is empty. The output format enabled otherwise this file is empty. The output format
is:: is::
<region>: [<start>-<end>] <reserved-size> bytes, Dumped: <dump-size> <region>: [<start>-<end>] <reserved-size> bytes, Dumped: <dump-size>
and for kernel DUMP region is:
DUMP: Src: <src-addr>, Dest: <dest-addr>, Size: <size>, Dumped: # bytes
e.g. e.g.
Contents when fadump is registered during first kernel:: Contents when FADump is registered during first kernel::
# cat /sys/kernel/debug/powerpc/fadump_region # cat /sys/kernel/debug/powerpc/fadump_region
CPU : [0x0000006ffb0000-0x0000006fff001f] 0x40020 bytes, Dumped: 0x0 CPU : [0x0000006ffb0000-0x0000006fff001f] 0x40020 bytes, Dumped: 0x0
HPTE: [0x0000006fff0020-0x0000006fff101f] 0x1000 bytes, Dumped: 0x0 HPTE: [0x0000006fff0020-0x0000006fff101f] 0x1000 bytes, Dumped: 0x0
DUMP: [0x0000006fff1020-0x0000007fff101f] 0x10000000 bytes, Dumped: 0x0 DUMP: [0x0000006fff1020-0x0000007fff101f] 0x10000000 bytes, Dumped: 0x0
Contents when fadump is active during second kernel:: Contents when FADump is active during second kernel::
# cat /sys/kernel/debug/powerpc/fadump_region # cat /sys/kernel/debug/powerpc/fadump_region
CPU : [0x0000006ffb0000-0x0000006fff001f] 0x40020 bytes, Dumped: 0x40020 CPU : [0x0000006ffb0000-0x0000006fff001f] 0x40020 bytes, Dumped: 0x40020
@ -268,6 +272,7 @@ Here is the list of files under powerpc debugfs:
DUMP: [0x0000006fff1020-0x0000007fff101f] 0x10000000 bytes, Dumped: 0x10000000 DUMP: [0x0000006fff1020-0x0000007fff101f] 0x10000000 bytes, Dumped: 0x10000000
: [0x00000010000000-0x0000006ffaffff] 0x5ffb0000 bytes, Dumped: 0x5ffb0000 : [0x00000010000000-0x0000006ffaffff] 0x5ffb0000 bytes, Dumped: 0x5ffb0000
NOTE: NOTE:
Please refer to Documentation/filesystems/debugfs.txt on Please refer to Documentation/filesystems/debugfs.txt on
how to mount the debugfs filesystem. how to mount the debugfs filesystem.
@ -278,7 +283,7 @@ TODO:
- Need to come up with the better approach to find out more - Need to come up with the better approach to find out more
accurate boot memory size that is required for a kernel to accurate boot memory size that is required for a kernel to
boot successfully when booted with restricted memory. boot successfully when booted with restricted memory.
- The fadump implementation introduces a fadump crash info structure - The FADump implementation introduces a FADump crash info structure
in the scratch area before the ELF core header. The idea of introducing in the scratch area before the ELF core header. The idea of introducing
this structure is to pass some important crash info data to the second this structure is to pass some important crash info data to the second
kernel which will help second kernel to populate ELF core header with kernel which will help second kernel to populate ELF core header with