The figures depicting FADump's (Firmware-Assisted Dump) memory layout
are missing some finer details like different memory regions and what
they represent. Improve the documentation by updating those details.
Signed-off-by: Hari Bathini <hbath...@linux.ibm.com>
---
Documentation/powerpc/firmware-assisted-dump.txt | 65 ++++++++++++----------
1 file changed, 35 insertions(+), 30 deletions(-)
diff --git a/Documentation/powerpc/firmware-assisted-dump.txt
b/Documentation/powerpc/firmware-assisted-dump.txt
index 18c5fee..059993b 100644
--- a/Documentation/powerpc/firmware-assisted-dump.txt
+++ b/Documentation/powerpc/firmware-assisted-dump.txt
@@ -74,8 +74,9 @@ as follows:
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.
+ size. This will make sure that this kernel (also, referred
+ to as second kernel or 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
@@ -125,48 +126,52 @@ 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 -->| |
- V V | Permanent Reservation | V
- +-----------+----------/ /---+---+----+-----------+----+------+
- | | |CPU|HPTE| DUMP |ELF | |
- +-----------+----------/ /---+---+----+-----------+----+------+
- | ^
- | |
- \ /
- -------------------------------------------
- Boot memory content gets transferred 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 | (Preserve area) | 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
+
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 | |
- +-----------+----------/ /---+---+----+-----------+----+------+
+ Low memory Top of memory
+ 0 boot memory size |
+ | |<------------- Reserved dump area --------------->|
+ V V |<---- Preserve area ----->| V
+ +-----------+----------/ /---+---+----+--------+---+----+------+
+ | | |CPU|HPTE| DUMP |HDR|ELF | |
+ +-----------+----------/ /---+---+----+--------+---+----+------+
| |
V V
Used by second /proc/vmcore
kernel to boot
Fig. 2
-Currently the dump will be copied from /proc/vmcore to a
-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) to save the dump works fine with
-minor modifications.
+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)
+to save the dump works fine with minor modifications. KDump scripts on
+major Distro releases have already been modified to work seemlessly (no
+user intervention in saving the dump) when FADump is used, instead of
+KDump, as dump mechanism.
The tools to examine the dump will be same as the ones
used for kdump.
How to enable firmware-assisted dump (fadump):
--------------------------------------
+---------------------------------------------
1. Set config option CONFIG_FA_DUMP=y and build kernel.
2. Boot into linux kernel with 'fadump=on' kernel cmdline option.
@@ -189,7 +194,7 @@ NOTE: 1. 'fadump_reserve_mem=' parameter has been
deprecated. Instead
old behaviour.
Sysfs/debugfs files:
-------------
+-------------------
Firmware-assisted dump feature uses sysfs file system to hold
the control files and debugfs file to display memory reserved region.
