From: Mahesh Salgaonkar <mah...@linux.vnet.ibm.com>
Metadata region that holds fadump header and ELF header is now placed at
the start of reserved memory area. Update the documentation accordingly
Signed-off-by: Mahesh Salgaonkar <mah...@linux.vnet.ibm.com>
---
Documentation/powerpc/firmware-assisted-dump.txt | 33 ++++++++++++++--------
1 file changed, 21 insertions(+), 12 deletions(-)
diff --git a/Documentation/powerpc/firmware-assisted-dump.txt
b/Documentation/powerpc/firmware-assisted-dump.txt
index bdd344aa18d9..30b32f879219 100644
--- a/Documentation/powerpc/firmware-assisted-dump.txt
+++ b/Documentation/powerpc/firmware-assisted-dump.txt
@@ -115,17 +115,26 @@ 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.
+The first kernel, during fadump registration, prepares ELF core header
+that contains necessary information for the coredump of the 1st kernel
+which includes its physical memory layout. This ELF header and some more
+additional data is stored in the area called metadata region at the start
+of the reserved memory area. The implementation maintains the compatibility
+between production/capture kernels irrespective of their kernel versions.
+Both combination older/newer and newer/older works fine.
+
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 | |
- +-----------+----------/ /---+---+----+-----------+----+------+
- | ^
- | |
+ +-----------+----------/ /---+----+---+----+-----------+------+
+ | | |ELF |CPU|HPTE| DUMP | |
+ +-----------+---------/ /----+----+---+----+-----------+------+
+ | ^ ^
+ | | |
+ | metadata region |
\ /
-------------------------------------------
Boot memory content gets transferred to
@@ -137,14 +146,14 @@ and HPTE region, in the case a crash does occur.
Low memory Top of memory
0 boot memory size |
- | |<------------- Reserved dump area ----------- -->|
+ | |<------------- Reserved dump area -------------->|
V V V
- +-----------+----------/ /---+---+----+-----------+----+------+
- | | |CPU|HPTE| DUMP |ELF | |
- +-----------+----------/ /---+---+----+-----------+----+------+
- | |
- V V
- Used by second /proc/vmcore
+ +-----------+----------/ /---+----+----+---------------+------+
+ | | |ELF |CPU|HPTE| DUMP | |
+ +-----------+----------/ /---+----+----+---------------+------+
+ | |
+ V V
+ Used by second /proc/vmcore
kernel to boot
Fig. 2
