[PATCH v3 06/16] powerpc/fadump: Update documentation about OPAL platform support
From: Hari Bathini <hbathini@linux.ibm.com>
Date: 2019-06-25 21:01:58
Subsystem:
documentation, the rest · Maintainers:
Jonathan Corbet, Linus Torvalds
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> --- Documentation/powerpc/firmware-assisted-dump.txt | 90 ++++++++++++---------- 1 file changed, 51 insertions(+), 39 deletions(-)
diff --git a/Documentation/powerpc/firmware-assisted-dump.txt b/Documentation/powerpc/firmware-assisted-dump.txt
index 62e75ef..844a229 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
@@ -93,7 +94,9 @@ 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. Implementation details: ----------------------
@@ -108,57 +111,66 @@ 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 | (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 Reservatio | | + V V | (Preserve area) | 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) 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) marked like this in the above figures + +---+ are not always present. For example, OPAL platform does not + have CPU & HPTE regions. + + 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)