[PATCH v2 2/2] fadump: update documentation about introduction of handover area
Hari Bathini
hbathini at linux.vnet.ibm.com
Tue Feb 7 23:38:09 AEDT 2017
Update documentation about introduction of handover area that includes
configuration details like extra parameters to append to capture
kernel.
Signed-off-by: Hari Bathini <hbathini at linux.vnet.ibm.com>
---
Documentation/powerpc/firmware-assisted-dump.txt | 83 ++++++++++++++--------
1 file changed, 53 insertions(+), 30 deletions(-)
diff --git a/Documentation/powerpc/firmware-assisted-dump.txt b/Documentation/powerpc/firmware-assisted-dump.txt
index 3007bc9..6c6a0e9 100644
--- a/Documentation/powerpc/firmware-assisted-dump.txt
+++ b/Documentation/powerpc/firmware-assisted-dump.txt
@@ -67,11 +67,17 @@ as follows:
-- The freshly booted kernel will notice that there is a new
node (ibm,dump-kernel) 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
- size. This will make sure that the second kernel will not
- touch any of the dump memory area.
+ there is crash data available from a previous boot. This
+ second kernel, where crash data is available from previous
+ boot, is referred to as capture kernel. The capture kernel,
+ early during the boot process, looks for a handover area
+ (see fig. 2), saved by the first kernel to be handed over
+ to it. This handover area contains certain config info like
+ extra parameters to append to the capture kernel. The capture
+ kernel applies this configuration accordingly. Later, reserves
+ rest of the memory above boot memory size effectively booting
+ with restricted memory size. This will make sure that the
+ capture kernel will not touch any of the dump memory area.
-- User-space tools will read /proc/vmcore to obtain the contents
of memory, which holds the previous crashed kernel dump in ELF
@@ -113,15 +119,18 @@ crash does occur.
o Memory Reservation during first kernel
- Low memory Top of memory
- 0 boot memory size |
- | | |<--Reserved dump area -->|
- V V | Permanent Reservation V
- +-----------+----------/ /----------+---+----+-----------+----+
- | | |CPU|HPTE| DUMP |ELF |
- +-----------+----------/ /----------+---+----+-----------+----+
- | ^
- | |
+ Low memory Top of memory
+ 0 |
+ | Handover area |
+ | | |
+ | | boot memory size |<-- Reserved dump area-->|
+ | | | | Permanent Reservation |
+ V V V V
+ +--+-+--------+----------/ /----------+---+----+-----------+----+
+ | | | | |CPU|HPTE| DUMP |ELF |
+ +--+-+--------+----------/ /----------+---+----+-----------+----+
+ |____ _______| ^
+ \/ |
\ /
-------------------------------------------
Boot memory content gets transferred to
@@ -129,18 +138,21 @@ crash does occur.
crash
Fig. 1
- o Memory Reservation during second kernel after crash
-
- Low memory Top of memory
- 0 boot memory size |
- | |<------------- Reserved dump area ----------- -->|
- V V V
- +-----------+----------/ /----------+---+----+-----------+----+
- | | |CPU|HPTE| DUMP |ELF |
- +-----------+----------/ /----------+---+----+-----------+----+
- | |
- V V
- Used by second /proc/vmcore
+ o Memory Reservation during capture (fadump) kernel after crash
+
+ Low memory Top of memory
+ 0 |
+ | Handover area |
+ | | |
+ | | boot memory size |
+ | | |<------------- Reserved dump area ----------- -->|
+ V V V V
+ +--+-+--------+----------/ /----------+---+----+-----------+----+
+ | | | | |CPU|HPTE| DUMP |ELF |
+ +--+-+--------+----------/ /----------+---+----+-----------+----+
+ |____ _______| |
+ \/ V
+ Used by capture /proc/vmcore
kernel to boot
Fig. 2
@@ -196,10 +208,21 @@ Here is the list of files under kernel sysfs:
be handled and vmcore will not be captured. This interface can be
easily integrated with kdump service start/stop.
+ /sys/kernel/fadump_cmdline_append
+
+ This is used to specify the extra parameters to append to capture
+ kernel. Typically used to pass parameters that reduce memory/resource
+ consumption for dump capture kernel. To pass parameters to append to
+ dump capture kernel:
+
+ echo "nr_cpus=1 kvm_cma_resv_ratio=0" > /sys/kernel/fadump_cmdline_append
+
+ This interface can be easily integrated with kdump service start/stop.
+
/sys/kernel/fadump_release_mem
This file is available only when fadump is active during
- second kernel. This is used to release the reserved memory
+ capture kernel. This is used to release the reserved memory
region that are held for saving crash dump. To release the
reserved memory echo 1 to it:
@@ -230,7 +253,7 @@ Here is the list of files under powerpc debugfs:
HPTE: [0x0000006fff0020-0x0000006fff101f] 0x1000 bytes, Dumped: 0x0
DUMP: [0x0000006fff1020-0x0000007fff101f] 0x10000000 bytes, Dumped: 0x0
- Contents when fadump is active during second kernel
+ Contents when fadump is active during capture kernel
# cat /sys/kernel/debug/powerpc/fadump_region
CPU : [0x0000006ffb0000-0x0000006fff001f] 0x40020 bytes, Dumped: 0x40020
@@ -249,8 +272,8 @@ TODO:
boot successfully when booted with restricted memory.
o The fadump implementation introduces a fadump crash info structure
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
- kernel which will help second kernel to populate ELF core header with
+ this structure is to pass some important crash info data to the capture
+ kernel which will help capture kernel to populate ELF core header with
correct data before it gets exported through /proc/vmcore. The current
design implementation does not address a possibility of introducing
additional fields (in future) to this structure without affecting
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