Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+======================
+Firmware-Assisted Dump
+======================
+
+July 2011
+
+The goal of firmware-assisted dump is to enable the dump of
+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
+  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
+  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
+  for dump, with a single operation of echo 1 > /sys/kernel/fadump_release_mem.
+- 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.
+
+Comparing with kdump or other strategies, firmware-assisted
+dump offers several strong, practical advantages:
+
+-  Unlike kdump, the system has been reset, and loaded
+   with a fresh copy of the kernel.  In particular,
+   PCI and I/O devices have been reinitialized and are
+   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
+   the system to the production configuration.
+
+The above can only be accomplished by coordination with,
+and assistance from the Power firmware. The procedure is
+as follows:
+
+-  The first kernel registers the sections of memory with the
+   Power firmware for dump preservation during OS initialization.
+   These registered sections of memory are reserved by the first
+   kernel during early boot.
+
+-  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
+         that is required for a kernel to boot successfully when
+         booted with restricted memory. By default, the boot memory
+         size will be the larger of 5% of system RAM or 256MB.
+         Alternatively, user can also specify boot memory size
+         through boot parameter 'crashkernel=' which will override
+         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
+         for boot memory dump preservation in case of a crash.
+
+-  After the low memory (boot memory) area has been saved, the
+   firmware will reset PCI and other hardware state.  It will
+   *not* clear the RAM. It will then launch the bootloader, as
+   normal.
+
+-  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 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
+   format. The userspace tools may copy this info to disk, or
+   network, nas, san, iscsi, etc. as desired.
+
+-  Once the userspace tool is done saving dump, it will echo
+   '1' to /sys/kernel/fadump_release_mem to release the reserved
+   memory back to general use, except the memory required for
+   next firmware-assisted dump registration.
+
+   e.g.::
+
+     # echo 1 > /sys/kernel/fadump_release_mem
+
+Please note that the firmware-assisted dump feature
+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/mpipl/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/firmware/opal/mpipl/release_core node.
+
+   e.g.
+     # echo 1 > /sys/firmware/opal/mpipl/release_core
+
+Implementation details:
+-----------------------
+
+During boot, a check is made to see if firmware supports
+this feature on that particular machine. If it does, then
+we check to see if an active dump is waiting for us. If yes
+then everything but boot memory size of RAM is reserved during
+early boot (See Fig. 2). This area is released once we finish
+collecting the dump from user land scripts (e.g. kdump scripts)
+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, 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
+  +-----------+-----/ /---+---+----+-------+-----+-----+----+--+
+  |           |           |///|////|  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 structure 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 --->|       |
+  +-----------+-----/ /---+---+----+-------+-----+-----+----+--+
+  |           |           |///|////|  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)
+to save the dump works fine with minor modifications. KDump scripts on
+major Distro releases have already been modified to work seamlessly (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):
+----------------------------------------------
+
+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.
+   Alternatively, user can boot linux kernel with 'fadump=nocma' to
+   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.
+
+NOTE:
+     1. 'fadump_reserve_mem=' parameter has been deprecated. Instead
+        use 'crashkernel=' to specify size of the memory to reserve
+        for boot memory dump preservation.
+     2. If firmware-assisted dump fails to reserve memory then it
+        will fallback to existing kdump mechanism if 'crashkernel='
+        option is set at kernel cmdline.
+     3. if user wants to capture all of user space memory and ok with
+        reserved memory not available to production system, then
+        'fadump=nocma' kernel parameter can be used to fallback to
+        old behaviour.
+
+Sysfs/debugfs files:
+--------------------
+
+Firmware-assisted dump feature uses sysfs file system to hold
+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.
+
+    - 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.
+
+ /sys/kernel/fadump_registered
+    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.
+
+    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
+    be handled and vmcore will not be captured. This interface can be
+    easily integrated with kdump service start/stop.
+
+ /sys/kernel/fadump/mem_reserved
+
+   This is used to display the memory reserved by FADump for saving the
+   crash dump.
+
+ /sys/kernel/fadump_release_mem
+    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::
+
+	echo 1  > /sys/kernel/fadump_release_mem
+
+    After echo 1, the content of the /sys/kernel/debug/powerpc/fadump_region
+    file will change to reflect the new memory reservations.
+
+    The existing userspace tools (kdump infrastructure) can be easily
+    enhanced to use this interface to release the memory reserved for
+    dump and continue without 2nd reboot.
+
+Note: /sys/kernel/fadump_release_opalcore sysfs has moved to
+      /sys/firmware/opal/mpipl/release_core
+
+ /sys/firmware/opal/mpipl/release_core
+
+    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/mpipl/core file. To
+    release this memory, echo '1' to it:
+
+    echo 1  > /sys/firmware/opal/mpipl/release_core
+
+Note: The following FADump sysfs files are deprecated.
+
++----------------------------------+--------------------------------+
+| Deprecated                       | Alternative                    |
++----------------------------------+--------------------------------+
+| /sys/kernel/fadump_enabled       | /sys/kernel/fadump/enabled     |
++----------------------------------+--------------------------------+
+| /sys/kernel/fadump_registered    | /sys/kernel/fadump/registered  |
++----------------------------------+--------------------------------+
+| /sys/kernel/fadump_release_mem   | /sys/kernel/fadump/release_mem |
++----------------------------------+--------------------------------+
+
+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
+    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::
+
+      # 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::
+
+      # cat /sys/kernel/debug/powerpc/fadump_region
+      CPU : [0x0000006ffb0000-0x0000006fff001f] 0x40020 bytes, Dumped: 0x40020
+      HPTE: [0x0000006fff0020-0x0000006fff101f] 0x1000 bytes, Dumped: 0x1000
+      DUMP: [0x0000006fff1020-0x0000007fff101f] 0x10000000 bytes, Dumped: 0x10000000
+          : [0x00000010000000-0x0000006ffaffff] 0x5ffb0000 bytes, Dumped: 0x5ffb0000
+
+
+NOTE:
+      Please refer to Documentation/filesystems/debugfs.rst on
+      how to mount the debugfs filesystem.
+
+
+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>
+
+This document is based on the original documentation written for phyp
+
+assisted dump by Linas Vepstas and Manish Ahuja.