@@ -46,10 +46,9 @@ as follows:
These registered sections of memory are reserved by the first
kernel during early boot.
-- When a system crashes, the Power firmware will save
- the low memory (boot memory of size larger of 5% of system RAM
- or 256MB) of RAM to the previous registered region. It will
- also save system registers, and hardware PTE's.
+- When system crashes, the Power firmware will copy the registered
+ low memory regions (boot memory) from source to destination area.
+ It will also save hardware PTE's.
NOTE:
The term 'boot memory' means size of the low memory chunk
@@ -61,9 +60,9 @@ as follows:
the default calculated size. Use this option if default
boot memory size is not sufficient for second kernel to
boot successfully. For syntax of crashkernel= parameter,
- refer to Documentation/admin-guide/kdump/kdump.rst. If any offset is
- provided in crashkernel= parameter, it will be ignored
- as FADump uses a predefined offset to reserve memory
+ refer to Documentation/admin-guide/kdump/kdump.rst. If any
+ offset is provided in crashkernel= parameter, it will be
+ ignored as FADump uses a predefined offset to reserve memory
for boot memory dump preservation in case of a crash.
- After the low memory (boot memory) area has been saved, the
@@ -71,8 +70,9 @@ as follows:
*not* clear the RAM. It will then launch the bootloader, as
normal.
-- The freshly booted kernel will notice that there is a new
- node (ibm,dump-kernel) in the device tree, indicating that
+- The freshly booted kernel will notice that there is a new node
+ (rtas/ibm,kernel-dump on pSeries or ibm,opal/dump/mpipl-boot
+ 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
@@ -95,8 +95,11 @@ as follows:
# echo 1 > /sys/kernel/fadump_release_mem
Please note that the firmware-assisted dump feature
-is only available on Power6 and above systems with recent
-firmware versions.
+is only available on POWER6 and above systems on pSeries
+(PowerVM) platform and POWER9 and above systems with OP940
+or later firmware versions on PowerNV (OPAL) platform.
+Note that, OPAL firmware exports ibm,opal/dump node when
+FADump is supported on PowerNV platform.
Implementation details:
-----------------------
@@ -111,57 +114,76 @@ that are run. If there is dump data, then the
/sys/kernel/fadump_release_mem file is created, and the reserved
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::
+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.
+
+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 | | 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 | | 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) |
+ |
+ |
+ Metadata: This area holds a metadata struture whose
+ address is registered with f/w and retrieved in the
+ second kernel after crash, on platforms that support
+ tags (OPAL). Having such structure with info needed
+ to process the crashdump eases dump capture process.
Fig. 1
o Memory Reservation during second kernel after crash
- Low memory Top of memory
- 0 boot memory size |
- | |<----------- Crash preserved area --------------->|
- V V |<-- Reserved dump area -->| V
- +-----------+----------/ /---+---+----+--------+---+----+------+
- | | |CPU|HPTE| DUMP |HDR|ELF | |
- +-----------+----------/ /---+---+----+--------+---+----+------+
- | |
- V V
- Used by second /proc/vmcore
+ Low memory Top of memory
+ 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
+
+ +---+
+ |///| -> Regions (CPU, HPTE & Metadata) marked like this in the above
+ +---+ figures are not always present. For example, OPAL platform
+ does not have CPU & HPTE regions while Metadata region is
+ not supported on pSeries currently.
+
Fig. 2
+
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)
With FADump support now available on both pseries and OPAL platforms, update FADump documentation with these details. Signed-off-by: Hari Bathini <hbathini@linux.ibm.com> --- Changes in v6: * Specific the firmware release versions that support MPIPL. Documentation/powerpc/firmware-assisted-dump.rst | 122 +++++++++++++--------- 1 file changed, 72 insertions(+), 50 deletions(-)