[PATCH 9/9] powerpc/fadump: Update documentation about OPAL platform support
Hari Bathini
hbathini at linux.ibm.com
Fri Dec 21 06:01:21 AEDT 2018
With FADump support now available on both pseries and OPAL platforms,
update FADump documentation with these details. Also, update about
backup area and why it is used.
Signed-off-by: Hari Bathini <hbathini at linux.ibm.com>
---
Documentation/powerpc/firmware-assisted-dump.txt | 102 ++++++++++++++--------
1 file changed, 64 insertions(+), 38 deletions(-)
diff --git a/Documentation/powerpc/firmware-assisted-dump.txt b/Documentation/powerpc/firmware-assisted-dump.txt
index 326f89c..eff9f38 100644
--- a/Documentation/powerpc/firmware-assisted-dump.txt
+++ b/Documentation/powerpc/firmware-assisted-dump.txt
@@ -70,7 +70,8 @@ as follows:
normal.
-- The freshly booted kernel will notice that there is a new
- node (ibm,dump-kernel) in the device tree, indicating that
+ node (ibm,dump-kernel on PSeries or ibm,opal/dump/result-table
+ on OPAL platform) in the device tree, indicating that
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
@@ -92,7 +93,20 @@ as follows:
Please note that the firmware-assisted dump feature
is only available on Power6 and above systems with recent
-firmware versions.
+firmware versions on PSeries (PowerVM) platform and Power9
+and above systems with recent firmware versions on PowerNV
+(OPAL) platform.
+
+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:
----------------------
@@ -108,56 +122,65 @@ 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 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. Since this reserved
-memory area is used only after the system crash, there is no point in
-blocking this significant chunk of memory from production kernel.
-Hence, the implementation uses the Linux kernel's Contiguous Memory
-Allocator (CMA) for memory reservation if CMA is configured for kernel.
-With CMA reservation this memory will be available for applications to
-use it, while kernel is prevented from using it. With this FADump will
-still be able to capture all of the kernel memory and most of the user
-space memory except the user pages that were present in CMA region.
+to 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.
+Since this reserved memory area is used only after the system crash,
+there is no point in blocking this significant chunk of memory from
+production kernel. Hence, the implementation uses the Linux kernel's
+Contiguous Memory Allocator (CMA) for memory reservation if CMA is
+configured for kernel. With CMA reservation this memory will be
+available for applications to use it, while kernel is prevented from
+using it. With this FADump will still be able to capture all of the
+kernel memory and most of the user 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 --->| |
- | | | 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
-
+ 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)
Fig. 1
o Memory Reservation during second kernel after crash
- Low memory Top of memory
- 0 boot memory size |
- | |<------------- Reserved dump area --------------->|
- V V |<---- Preserve area ----->| V
- +-----------+----------/ /---+---+----+--------+---+----+------+
- | | |CPU|HPTE| 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
kernel to boot
Fig. 2
+ +---+
+ |///| -> 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
user intervention. The dump data available through /proc/vmcore will be
in ELF format. Hence the existing kdump infrastructure (kdump scripts)
@@ -289,7 +312,10 @@ 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 at linux.vnet.ibm.com>
This document is based on the original documentation written for phyp
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