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Diffstat (limited to 'Documentation/powerpc/firmware-assisted-dump.rst')
| -rw-r--r-- | Documentation/powerpc/firmware-assisted-dump.rst | 122 |
1 files changed, 72 insertions, 50 deletions
diff --git a/Documentation/powerpc/firmware-assisted-dump.rst b/Documentation/powerpc/firmware-assisted-dump.rst index d912755067d2..ab578ac64c09 100644 --- a/Documentation/powerpc/firmware-assisted-dump.rst +++ b/Documentation/powerpc/firmware-assisted-dump.rst @@ -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) |