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 0c41d6d..e9b4e3c 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.