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-rw-r--r--Documentation/arch/powerpc/firmware-assisted-dump.rst91
1 files changed, 42 insertions, 49 deletions
diff --git a/Documentation/arch/powerpc/firmware-assisted-dump.rst b/Documentation/arch/powerpc/firmware-assisted-dump.rst
index e363fc4852..7e37aadd1f 100644
--- a/Documentation/arch/powerpc/firmware-assisted-dump.rst
+++ b/Documentation/arch/powerpc/firmware-assisted-dump.rst
@@ -134,12 +134,12 @@ 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
-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.
+hold CPU state, HPTE region, boot memory dump, and FADump header 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.
Since this reserved memory area is used only after the system crash,
there is no point in blocking this significant chunk of memory from
@@ -153,22 +153,22 @@ 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 Reservation | |
- V V | | V
- +-----------+-----/ /---+---+----+-------+-----+-----+----+--+
- | | |///|////| DUMP | HDR | ELF |////| |
- +-----------+-----/ /---+---+----+-------+-----+-----+----+--+
- | ^ ^ ^ ^ ^
- | | | | | |
- \ CPU HPTE / | |
- ------------------------------ | |
- Boot memory content gets transferred | |
- to reserved area by firmware at the | |
- time of crash. | |
- FADump Header |
- (meta area) |
+ Low memory Top of memory
+ 0 boot memory size |<------ Reserved dump area ----->| |
+ | | | Permanent Reservation | |
+ V V | | V
+ +-----------+-----/ /---+---+----+-----------+-------+----+-----+
+ | | |///|////| DUMP | HDR |////| |
+ +-----------+-----/ /---+---+----+-----------+-------+----+-----+
+ | ^ ^ ^ ^ ^
+ | | | | | |
+ \ CPU HPTE / | |
+ -------------------------------- | |
+ Boot memory content gets transferred | |
+ to reserved area by firmware at the | |
+ time of crash. | |
+ FADump Header |
+ (meta area) |
|
|
Metadata: This area holds a metadata structure whose
@@ -186,13 +186,20 @@ that were present in CMA region::
0 boot memory size |
| |<------------ Crash preserved area ------------>|
V V |<--- Reserved dump area --->| |
- +-----------+-----/ /---+---+----+-------+-----+-----+----+--+
- | | |///|////| DUMP | HDR | ELF |////| |
- +-----------+-----/ /---+---+----+-------+-----+-----+----+--+
- | |
- V V
- Used by second /proc/vmcore
- kernel to boot
+ +----+---+--+-----/ /---+---+----+-------+-----+-----+-------+
+ | |ELF| | |///|////| DUMP | HDR |/////| |
+ +----+---+--+-----/ /---+---+----+-------+-----+-----+-------+
+ | | | | | |
+ ----- ------------------------------ ---------------
+ \ | |
+ \ | |
+ \ | |
+ \ | ----------------------------
+ \ | /
+ \ | /
+ \ | /
+ /proc/vmcore
+
+---+
|///| -> Regions (CPU, HPTE & Metadata) marked like this in the above
@@ -200,6 +207,12 @@ that were present in CMA region::
does not have CPU & HPTE regions while Metadata region is
not supported on pSeries currently.
+ +---+
+ |ELF| -> elfcorehdr, it is created in second kernel after crash.
+ +---+
+
+ Note: Memory from 0 to the boot memory size is used by second kernel
+
Fig. 2
@@ -353,26 +366,6 @@ TODO:
- Need to come up with the better approach to find out more
accurate boot memory size that is required for a kernel to
boot successfully when booted with restricted memory.
- - 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
- 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
- compatibility. Need to come up with the better approach to address this.
-
- The possible approaches are:
-
- 1. Introduce version field for version tracking, bump up the version
- whenever a new field is added to the structure in future. The version
- field can be used to find out what fields are valid for the current
- version of the structure.
- 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.
Author: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>