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Diffstat (limited to 'Documentation/powerpc/firmware-assisted-dump.rst')
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1 files changed, 140 insertions, 80 deletions
diff --git a/Documentation/powerpc/firmware-assisted-dump.rst b/Documentation/powerpc/firmware-assisted-dump.rst index 9ca12830a48e..0455a78486d5 100644 --- a/Documentation/powerpc/firmware-assisted-dump.rst +++ b/Documentation/powerpc/firmware-assisted-dump.rst @@ -9,18 +9,18 @@ a crashed system, and to do so from a fully-reset system, and to minimize the total elapsed time until the system is back in production use. -- Firmware assisted dump (fadump) infrastructure is intended to replace +- Firmware-Assisted Dump (FADump) infrastructure is intended to replace the existing phyp assisted dump. - Fadump uses the same firmware interfaces and memory reservation model as phyp assisted dump. -- Unlike phyp dump, fadump exports the memory dump through /proc/vmcore +- Unlike phyp dump, FADump exports the memory dump through /proc/vmcore in the ELF format in the same way as kdump. This helps us reuse the kdump infrastructure for dump capture and filtering. - Unlike phyp dump, userspace tool does not need to refer any sysfs interface while reading /proc/vmcore. -- Unlike phyp dump, fadump allows user to release all the memory reserved +- Unlike phyp dump, FADump allows user to release all the memory reserved for dump, with a single operation of echo 1 > /sys/kernel/fadump_release_mem. -- Once enabled through kernel boot parameter, fadump can be +- Once enabled through kernel boot parameter, FADump can be started/stopped through /sys/kernel/fadump_registered interface (see sysfs files section below) and can be easily integrated with kdump service start/stop init scripts. @@ -34,7 +34,7 @@ dump offers several strong, practical advantages: in a clean, consistent state. - Once the dump is copied out, the memory that held the dump is immediately available to the running kernel. And therefore, - unlike kdump, fadump doesn't need a 2nd reboot to get back + unlike kdump, FADump doesn't need a 2nd reboot to get back the system to the production configuration. The above can only be accomplished by coordination with, @@ -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 @@ -71,13 +70,15 @@ 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 - size. This will make sure that the second kernel will not - touch any of the dump memory area. + size. This will make sure that this kernel (also, referred + to as second kernel or capture kernel) will not touch any + of the dump memory area. - User-space tools will read /proc/vmcore to obtain the contents of memory, which holds the previous crashed kernel dump in ELF @@ -94,8 +95,30 @@ 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. + +On OPAL based machines, system first boots into an intermittent +kernel (referred to as petitboot kernel) before booting into the +capture kernel. This kernel would have minimal kernel and/or +userspace support to process crash data. Such kernel needs to +preserve previously crash'ed kernel's memory for the subsequent +capture kernel boot to process this crash data. Kernel config +option CONFIG_PRESERVE_FA_DUMP has to be enabled on such kernel +to ensure that crash data is preserved to process later. + +-- On OPAL based machines (PowerNV), if the kernel is build with + CONFIG_OPAL_CORE=y, OPAL memory at the time of crash is also + exported as /sys/firmware/opal/core file. This procfs file is + helpful in debugging OPAL crashes with GDB. The kernel memory + used for exporting this procfs file can be released by echo'ing + '1' to /sys/kernel/fadump_release_opalcore node. + + e.g. + # echo 1 > /sys/kernel/fadump_release_opalcore Implementation details: ----------------------- @@ -110,72 +133,95 @@ 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 -->| | - V V | Permanent Reservation | V - +-----------+----------/ /---+---+----+-----------+----+------+ - | | |CPU|HPTE| DUMP |ELF | | - +-----------+----------/ /---+---+----+-----------+----+------+ - | ^ - | | - \ / - ------------------------------------------- - Boot memory content gets transferred 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 | - | |<------------- Reserved dump area ----------- -->| - V V V - +-----------+----------/ /---+---+----+-----------+----+------+ - | | |CPU|HPTE| DUMP |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 -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) to save the dump works fine with -minor modifications. + +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) +to save the dump works fine with minor modifications. KDump scripts on +major Distro releases have already been modified to work seemlessly (no +user intervention in saving the dump) when FADump is used, instead of +KDump, as dump mechanism. The tools to examine the dump will be same as the ones used for kdump. -How to enable firmware-assisted dump (fadump): +How to enable firmware-assisted dump (FADump): ---------------------------------------------- 1. Set config option CONFIG_FA_DUMP=y and build kernel. 2. Boot into linux kernel with 'fadump=on' kernel cmdline option. - By default, fadump reserved memory will be initialized as CMA area. + By default, FADump reserved memory will be initialized as CMA area. Alternatively, user can boot linux kernel with 'fadump=nocma' to - prevent fadump to use CMA. + prevent FADump to use CMA. 3. Optionally, user can also set 'crashkernel=' kernel cmdline to specify size of the memory to reserve for boot memory dump preservation. @@ -201,29 +247,29 @@ the control files and debugfs file to display memory reserved region. Here is the list of files under kernel sysfs: /sys/kernel/fadump_enabled - This is used to display the fadump status. + This is used to display the FADump status. - - 0 = fadump is disabled - - 1 = fadump is enabled + - 0 = FADump is disabled + - 1 = FADump is enabled This interface can be used by kdump init scripts to identify if - fadump is enabled in the kernel and act accordingly. + FADump is enabled in the kernel and act accordingly. /sys/kernel/fadump_registered - This is used to display the fadump registration status as well - as to control (start/stop) the fadump registration. + This is used to display the FADump registration status as well + as to control (start/stop) the FADump registration. - - 0 = fadump is not registered. - - 1 = fadump is registered and ready to handle system crash. + - 0 = FADump is not registered. + - 1 = FADump is registered and ready to handle system crash. - To register fadump echo 1 > /sys/kernel/fadump_registered and + To register FADump echo 1 > /sys/kernel/fadump_registered and echo 0 > /sys/kernel/fadump_registered for un-register and stop the - fadump. Once the fadump is un-registered, the system crash will not + FADump. Once the FADump is un-registered, the system crash will not be handled and vmcore will not be captured. This interface can be easily integrated with kdump service start/stop. /sys/kernel/fadump_release_mem - This file is available only when fadump is active during + This file is available only when FADump is active during second kernel. This is used to release the reserved memory region that are held for saving crash dump. To release the reserved memory echo 1 to it:: @@ -237,25 +283,38 @@ Here is the list of files under kernel sysfs: enhanced to use this interface to release the memory reserved for dump and continue without 2nd reboot. + /sys/kernel/fadump_release_opalcore + + This file is available only on OPAL based machines when FADump is + active during capture kernel. This is used to release the memory + used by the kernel to export /sys/firmware/opal/core file. To + release this memory, echo '1' to it: + + echo 1 > /sys/kernel/fadump_release_opalcore + Here is the list of files under powerpc debugfs: (Assuming debugfs is mounted on /sys/kernel/debug directory.) /sys/kernel/debug/powerpc/fadump_region - This file shows the reserved memory regions if fadump is + This file shows the reserved memory regions if FADump is enabled otherwise this file is empty. The output format is:: <region>: [<start>-<end>] <reserved-size> bytes, Dumped: <dump-size> + and for kernel DUMP region is: + + DUMP: Src: <src-addr>, Dest: <dest-addr>, Size: <size>, Dumped: # bytes + e.g. - Contents when fadump is registered during first kernel:: + Contents when FADump is registered during first kernel:: # cat /sys/kernel/debug/powerpc/fadump_region CPU : [0x0000006ffb0000-0x0000006fff001f] 0x40020 bytes, Dumped: 0x0 HPTE: [0x0000006fff0020-0x0000006fff101f] 0x1000 bytes, Dumped: 0x0 DUMP: [0x0000006fff1020-0x0000007fff101f] 0x10000000 bytes, Dumped: 0x0 - Contents when fadump is active during second kernel:: + Contents when FADump is active during second kernel:: # cat /sys/kernel/debug/powerpc/fadump_region CPU : [0x0000006ffb0000-0x0000006fff001f] 0x40020 bytes, Dumped: 0x40020 @@ -263,6 +322,7 @@ Here is the list of files under powerpc debugfs: DUMP: [0x0000006fff1020-0x0000007fff101f] 0x10000000 bytes, Dumped: 0x10000000 : [0x00000010000000-0x0000006ffaffff] 0x5ffb0000 bytes, Dumped: 0x5ffb0000 + NOTE: Please refer to Documentation/filesystems/debugfs.txt on how to mount the debugfs filesystem. @@ -273,7 +333,7 @@ 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 + - 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 |