[PATCH 18/18] powerpc/fadump: Update documentation about backup area support
From: Hari Bathini <hbathini@linux.ibm.com>
Date: 2019-02-21 18:08:53
Subsystem:
documentation, the rest · Maintainers:
Jonathan Corbet, Linus Torvalds
With backup area support available for FADump on PowerNV platform, update FADump documentation with these details. Signed-off-by: Hari Bathini <hbathini@linux.ibm.com> --- Documentation/powerpc/firmware-assisted-dump.txt | 71 +++++++++++++--------- 1 file changed, 43 insertions(+), 28 deletions(-)
diff --git a/Documentation/powerpc/firmware-assisted-dump.txt b/Documentation/powerpc/firmware-assisted-dump.txt
index 6411449..42a0065 100644
--- a/Documentation/powerpc/firmware-assisted-dump.txt
+++ b/Documentation/powerpc/firmware-assisted-dump.txt@@ -117,6 +117,17 @@ to ensure that crash data is preserved to process later. e.g. # echo 1 > /sys/kernel/fadump_release_opalcore +To process dump on OPAL platform, additional meta data (PIR to +Logical CPU map) from the crashing kernel is required. This info +has to be backed up by the crashing kernel for capture kernel to +use it in making sense of the register state data provided by the +F/W. The start address of the area where this info is backed up +is stored at the tail end of FADump crash info header. To indicate +the presence of this additional meta data (backup info), the magic +number field in FADump crash info header is overloaded as version +identifier. + + Implementation details: ----------------------
@@ -131,12 +142,12 @@ that are run. If there is dump data, then the memory is held. 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 +hold CPU state, HPTE region, boot memory dump, FADump header, elfcore +header and backup area, 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. +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
@@ -150,19 +161,19 @@ 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 Reservatio | | - V V | (Preserve area) | V - +-----------+--------/ /---+---+----+-------+-----+-----+-------+ - | | |///|////| DUMP | HDR | ELF | | - +-----------+--------/ /---+---+----+-------+-----+-----+-------+ - | ^ ^ ^ ^ - | | | | | - \ CPU HPTE / | - --------------------------------- | - Boot memory content gets transferred | - to reserved area by firmware at the | + Low memory Top of memory + 0 boot memory size |<---- Reserved dump area ---->| | + | | | Permanent Reservation | | + V V | (Preserve area) | V + +-----------+--------/ /---+---+----+-------+-----+----+--+-------+ + | | |///|////| DUMP |HDR|/|ELF |//| | + +-----------+--------/ /---+---+----+-------+-----+----+--+-------+ + | ^ ^ ^ ^ | ^^ + | | | | | | || + \ CPU HPTE / | \ / Backup Info + --------------------------------- | ---- + Boot memory content gets transferred | Start address of + to reserved area by firmware at the | Backup Info. time of crash. | FADump Header (meta area)
@@ -171,13 +182,13 @@ that were present in CMA region. o Memory Reservation during second kernel after crash - Low memory Top of memory - 0 boot memory size | - | |<--------------- Reserved dump area -------------->| - V V |<---- Preserve area ------->| | - +-----------+--------/ /---+---+----+-------+-----+-----+-------+ - | | |///|////| DUMP | HDR | ELF | | - +-----------+--------/ /---+---+----+-------+-----+-----+-------+ + Low memory Top of memory + 0 boot memory size | + | |<--------------- Reserved dump area ---------------->| + V V |<----- Preserve area -------->| | + +-----------+--------/ /---+---+----+-------+-----+----+--+-------+ + | | |///|////| DUMP |HDR|/|ELF |//| | + +-----------+--------/ /---+---+----+-------+-----+----+--+-------+ | | V V Used by second /proc/vmcore
@@ -185,9 +196,10 @@ that were present in CMA region. Fig. 2 +---+ - |///| -> Regions (CPU & HPTE) marked like this in the above figures - +---+ are not always present. For example, OPAL platform does not - have CPU & HPTE regions. + |///| -> Regions (CPU, HPTE, HDR extension & Backup area) marked + +---+ like this in the above figures are not always present. + For example, OPAL platform does not have CPU & HPTE regions + while PSeries platform doesn't use Backup area currently. Currently the dump will be copied from /proc/vmcore to a new file upon
@@ -330,7 +342,10 @@ TODO: 2. Reserve the area of predefined size (say PAGE_SIZE) for this structure and have unused area as reserved (initialized to zero) for future field additions. + The advantage of approach 1 over 2 is we don't need to reserve extra space. + Using approach 1 to provide additional meta data on OPAL platform while + overloading magic number field as version identifier for version tracking. --- Author: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com> This document is based on the original documentation written for phyp