diff options
Diffstat (limited to 'Documentation/arch/powerpc/firmware-assisted-dump.rst')
| -rw-r--r-- | Documentation/arch/powerpc/firmware-assisted-dump.rst | 91 |
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 e363fc48529a..7e37aadd1f77 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> |