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authorLinus Torvalds <torvalds@linux-foundation.org>2012-03-21 21:55:10 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2012-03-21 21:55:10 -0400
commit5375871d432ae9fc581014ac117b96aaee3cd0c7 (patch)
treebe98e8255b0f927fb920fb532a598b93fa140dbe /Documentation
parentb57cb7231b2ce52d3dda14a7b417ae125fb2eb97 (diff)
parentdfbc2d75c1bd47c3186fa91f1655ea2f3825b0ec (diff)
Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/benh/powerpc
Pull powerpc merge from Benjamin Herrenschmidt: "Here's the powerpc batch for this merge window. It is going to be a bit more nasty than usual as in touching things outside of arch/powerpc mostly due to the big iSeriesectomy :-) We finally got rid of the bugger (legacy iSeries support) which was a PITA to maintain and that nobody really used anymore. Here are some of the highlights: - Legacy iSeries is gone. Thanks Stephen ! There's still some bits and pieces remaining if you do a grep -ir series arch/powerpc but they are harmless and will be removed in the next few weeks hopefully. - The 'fadump' functionality (Firmware Assisted Dump) replaces the previous (equivalent) "pHyp assisted dump"... it's a rewrite of a mechanism to get the hypervisor to do crash dumps on pSeries, the new implementation hopefully being much more reliable. Thanks Mahesh Salgaonkar. - The "EEH" code (pSeries PCI error handling & recovery) got a big spring cleaning, motivated by the need to be able to implement a new backend for it on top of some new different type of firwmare. The work isn't complete yet, but a good chunk of the cleanups is there. Note that this adds a field to struct device_node which is not very nice and which Grant objects to. I will have a patch soon that moves that to a powerpc private data structure (hopefully before rc1) and we'll improve things further later on (hopefully getting rid of the need for that pointer completely). Thanks Gavin Shan. - I dug into our exception & interrupt handling code to improve the way we do lazy interrupt handling (and make it work properly with "edge" triggered interrupt sources), and while at it found & fixed a wagon of issues in those areas, including adding support for page fault retry & fatal signals on page faults. - Your usual random batch of small fixes & updates, including a bunch of new embedded boards, both Freescale and APM based ones, etc..." I fixed up some conflicts with the generalized irq-domain changes from Grant Likely, hopefully correctly. * 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/benh/powerpc: (141 commits) powerpc/ps3: Do not adjust the wrapper load address powerpc: Remove the rest of the legacy iSeries include files powerpc: Remove the remaining CONFIG_PPC_ISERIES pieces init: Remove CONFIG_PPC_ISERIES powerpc: Remove FW_FEATURE ISERIES from arch code tty/hvc_vio: FW_FEATURE_ISERIES is no longer selectable powerpc/spufs: Fix double unlocks powerpc/5200: convert mpc5200 to use of_platform_populate() powerpc/mpc5200: add options to mpc5200_defconfig powerpc/mpc52xx: add a4m072 board support powerpc/mpc5200: update mpc5200_defconfig to fit for charon board Documentation/powerpc/mpc52xx.txt: Checkpatch cleanup powerpc/44x: Add additional device support for APM821xx SoC and Bluestone board powerpc/44x: Add support PCI-E for APM821xx SoC and Bluestone board MAINTAINERS: Update PowerPC 4xx tree powerpc/44x: The bug fixed support for APM821xx SoC and Bluestone board powerpc: document the FSL MPIC message register binding powerpc: add support for MPIC message register API powerpc/fsl: Added aliased MSIIR register address to MSI node in dts powerpc/85xx: mpc8548cds - add 36-bit dts ...
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/devicetree/bindings/powerpc/fsl/mpic-msgr.txt63
-rw-r--r--Documentation/devicetree/bindings/powerpc/fsl/mpic.txt22
-rw-r--r--Documentation/devicetree/bindings/powerpc/fsl/msi-pic.txt6
-rw-r--r--Documentation/powerpc/firmware-assisted-dump.txt270
-rw-r--r--Documentation/powerpc/mpc52xx.txt12
-rw-r--r--Documentation/powerpc/phyp-assisted-dump.txt127
6 files changed, 364 insertions, 136 deletions
diff --git a/Documentation/devicetree/bindings/powerpc/fsl/mpic-msgr.txt b/Documentation/devicetree/bindings/powerpc/fsl/mpic-msgr.txt
new file mode 100644
index 000000000000..bc8ded641ab6
--- /dev/null
+++ b/Documentation/devicetree/bindings/powerpc/fsl/mpic-msgr.txt
@@ -0,0 +1,63 @@
1* FSL MPIC Message Registers
2
3This binding specifies what properties must be available in the device tree
4representation of the message register blocks found in some FSL MPIC
5implementations.
6
7Required properties:
8
9 - compatible: Specifies the compatibility list for the message register
10 block. The type shall be <string-list> and the value shall be of the form
11 "fsl,mpic-v<version>-msgr", where <version> is the version number of
12 the MPIC containing the message registers.
13
14 - reg: Specifies the base physical address(s) and size(s) of the
15 message register block's addressable register space. The type shall be
16 <prop-encoded-array>.
17
18 - interrupts: Specifies a list of interrupt-specifiers which are available
19 for receiving interrupts. Interrupt-specifier consists of two cells: first
20 cell is interrupt-number and second cell is level-sense. The type shall be
21 <prop-encoded-array>.
22
23Optional properties:
24
25 - mpic-msgr-receive-mask: Specifies what registers in the containing block
26 are allowed to receive interrupts. The value is a bit mask where a set
27 bit at bit 'n' indicates that message register 'n' can receive interrupts.
28 Note that "bit 'n'" is numbered from LSB for PPC hardware. The type shall
29 be <u32>. If not present, then all of the message registers in the block
30 are available.
31
32Aliases:
33
34 An alias should be created for every message register block. They are not
35 required, though. However, a particular implementation of this binding
36 may require aliases to be present. Aliases are of the form
37 'mpic-msgr-block<n>', where <n> is an integer specifying the block's number.
38 Numbers shall start at 0.
39
40Example:
41
42 aliases {
43 mpic-msgr-block0 = &mpic_msgr_block0;
44 mpic-msgr-block1 = &mpic_msgr_block1;
45 };
46
47 mpic_msgr_block0: mpic-msgr-block@41400 {
48 compatible = "fsl,mpic-v3.1-msgr";
49 reg = <0x41400 0x200>;
50 // Message registers 0 and 2 in this block can receive interrupts on
51 // sources 0xb0 and 0xb2, respectively.
52 interrupts = <0xb0 2 0xb2 2>;
53 mpic-msgr-receive-mask = <0x5>;
54 };
55
56 mpic_msgr_block1: mpic-msgr-block@42400 {
57 compatible = "fsl,mpic-v3.1-msgr";
58 reg = <0x42400 0x200>;
59 // Message registers 0 and 2 in this block can receive interrupts on
60 // sources 0xb4 and 0xb6, respectively.
61 interrupts = <0xb4 2 0xb6 2>;
62 mpic-msgr-receive-mask = <0x5>;
63 };
diff --git a/Documentation/devicetree/bindings/powerpc/fsl/mpic.txt b/Documentation/devicetree/bindings/powerpc/fsl/mpic.txt
index 2cf38bd841fd..dc5744636a57 100644
--- a/Documentation/devicetree/bindings/powerpc/fsl/mpic.txt
+++ b/Documentation/devicetree/bindings/powerpc/fsl/mpic.txt
@@ -56,7 +56,27 @@ PROPERTIES
56 to the client. The presence of this property also mandates 56 to the client. The presence of this property also mandates
57 that any initialization related to interrupt sources shall 57 that any initialization related to interrupt sources shall
58 be limited to sources explicitly referenced in the device tree. 58 be limited to sources explicitly referenced in the device tree.
59 59
60 - big-endian
61 Usage: optional
62 Value type: <empty>
63 If present the MPIC will be assumed to be big-endian. Some
64 device-trees omit this property on MPIC nodes even when the MPIC is
65 in fact big-endian, so certain boards override this property.
66
67 - single-cpu-affinity
68 Usage: optional
69 Value type: <empty>
70 If present the MPIC will be assumed to only be able to route
71 non-IPI interrupts to a single CPU at a time (EG: Freescale MPIC).
72
73 - last-interrupt-source
74 Usage: optional
75 Value type: <u32>
76 Some MPICs do not correctly report the number of hardware sources
77 in the global feature registers. If specified, this field will
78 override the value read from MPIC_GREG_FEATURE_LAST_SRC.
79
60INTERRUPT SPECIFIER DEFINITION 80INTERRUPT SPECIFIER DEFINITION
61 81
62 Interrupt specifiers consists of 4 cells encoded as 82 Interrupt specifiers consists of 4 cells encoded as
diff --git a/Documentation/devicetree/bindings/powerpc/fsl/msi-pic.txt b/Documentation/devicetree/bindings/powerpc/fsl/msi-pic.txt
index 5d586e1ccaf5..5693877ab377 100644
--- a/Documentation/devicetree/bindings/powerpc/fsl/msi-pic.txt
+++ b/Documentation/devicetree/bindings/powerpc/fsl/msi-pic.txt
@@ -6,8 +6,10 @@ Required properties:
6 etc.) and the second is "fsl,mpic-msi" or "fsl,ipic-msi" depending on 6 etc.) and the second is "fsl,mpic-msi" or "fsl,ipic-msi" depending on
7 the parent type. 7 the parent type.
8 8
9- reg : should contain the address and the length of the shared message 9- reg : It may contain one or two regions. The first region should contain
10 interrupt register set. 10 the address and the length of the shared message interrupt register set.
11 The second region should contain the address of aliased MSIIR register for
12 platforms that have such an alias.
11 13
12- msi-available-ranges: use <start count> style section to define which 14- msi-available-ranges: use <start count> style section to define which
13 msi interrupt can be used in the 256 msi interrupts. This property is 15 msi interrupt can be used in the 256 msi interrupts. This property is
diff --git a/Documentation/powerpc/firmware-assisted-dump.txt b/Documentation/powerpc/firmware-assisted-dump.txt
new file mode 100644
index 000000000000..3007bc98af28
--- /dev/null
+++ b/Documentation/powerpc/firmware-assisted-dump.txt
@@ -0,0 +1,270 @@
1
2 Firmware-Assisted Dump
3 ------------------------
4 July 2011
5
6The goal of firmware-assisted dump is to enable the dump of
7a crashed system, and to do so from a fully-reset system, and
8to minimize the total elapsed time until the system is back
9in production use.
10
11- Firmware assisted dump (fadump) infrastructure is intended to replace
12 the existing phyp assisted dump.
13- Fadump uses the same firmware interfaces and memory reservation model
14 as phyp assisted dump.
15- Unlike phyp dump, fadump exports the memory dump through /proc/vmcore
16 in the ELF format in the same way as kdump. This helps us reuse the
17 kdump infrastructure for dump capture and filtering.
18- Unlike phyp dump, userspace tool does not need to refer any sysfs
19 interface while reading /proc/vmcore.
20- Unlike phyp dump, fadump allows user to release all the memory reserved
21 for dump, with a single operation of echo 1 > /sys/kernel/fadump_release_mem.
22- Once enabled through kernel boot parameter, fadump can be
23 started/stopped through /sys/kernel/fadump_registered interface (see
24 sysfs files section below) and can be easily integrated with kdump
25 service start/stop init scripts.
26
27Comparing with kdump or other strategies, firmware-assisted
28dump offers several strong, practical advantages:
29
30-- Unlike kdump, the system has been reset, and loaded
31 with a fresh copy of the kernel. In particular,
32 PCI and I/O devices have been reinitialized and are
33 in a clean, consistent state.
34-- Once the dump is copied out, the memory that held the dump
35 is immediately available to the running kernel. And therefore,
36 unlike kdump, fadump doesn't need a 2nd reboot to get back
37 the system to the production configuration.
38
39The above can only be accomplished by coordination with,
40and assistance from the Power firmware. The procedure is
41as follows:
42
43-- The first kernel registers the sections of memory with the
44 Power firmware for dump preservation during OS initialization.
45 These registered sections of memory are reserved by the first
46 kernel during early boot.
47
48-- When a system crashes, the Power firmware will save
49 the low memory (boot memory of size larger of 5% of system RAM
50 or 256MB) of RAM to the previous registered region. It will
51 also save system registers, and hardware PTE's.
52
53 NOTE: The term 'boot memory' means size of the low memory chunk
54 that is required for a kernel to boot successfully when
55 booted with restricted memory. By default, the boot memory
56 size will be the larger of 5% of system RAM or 256MB.
57 Alternatively, user can also specify boot memory size
58 through boot parameter 'fadump_reserve_mem=' which will
59 override the default calculated size. Use this option
60 if default boot memory size is not sufficient for second
61 kernel to boot successfully.
62
63-- After the low memory (boot memory) area has been saved, the
64 firmware will reset PCI and other hardware state. It will
65 *not* clear the RAM. It will then launch the bootloader, as
66 normal.
67
68-- The freshly booted kernel will notice that there is a new
69 node (ibm,dump-kernel) in the device tree, indicating that
70 there is crash data available from a previous boot. During
71 the early boot OS will reserve rest of the memory above
72 boot memory size effectively booting with restricted memory
73 size. This will make sure that the second kernel will not
74 touch any of the dump memory area.
75
76-- User-space tools will read /proc/vmcore to obtain the contents
77 of memory, which holds the previous crashed kernel dump in ELF
78 format. The userspace tools may copy this info to disk, or
79 network, nas, san, iscsi, etc. as desired.
80
81-- Once the userspace tool is done saving dump, it will echo
82 '1' to /sys/kernel/fadump_release_mem to release the reserved
83 memory back to general use, except the memory required for
84 next firmware-assisted dump registration.
85
86 e.g.
87 # echo 1 > /sys/kernel/fadump_release_mem
88
89Please note that the firmware-assisted dump feature
90is only available on Power6 and above systems with recent
91firmware versions.
92
93Implementation details:
94----------------------
95
96During boot, a check is made to see if firmware supports
97this feature on that particular machine. If it does, then
98we check to see if an active dump is waiting for us. If yes
99then everything but boot memory size of RAM is reserved during
100early boot (See Fig. 2). This area is released once we finish
101collecting the dump from user land scripts (e.g. kdump scripts)
102that are run. If there is dump data, then the
103/sys/kernel/fadump_release_mem file is created, and the reserved
104memory is held.
105
106If there is no waiting dump data, then only the memory required
107to hold CPU state, HPTE region, boot memory dump and elfcore
108header, is reserved at the top of memory (see Fig. 1). This area
109is *not* released: this region will be kept permanently reserved,
110so that it can act as a receptacle for a copy of the boot memory
111content in addition to CPU state and HPTE region, in the case a
112crash does occur.
113
114 o Memory Reservation during first kernel
115
116 Low memory Top of memory
117 0 boot memory size |
118 | | |<--Reserved dump area -->|
119 V V | Permanent Reservation V
120 +-----------+----------/ /----------+---+----+-----------+----+
121 | | |CPU|HPTE| DUMP |ELF |
122 +-----------+----------/ /----------+---+----+-----------+----+
123 | ^
124 | |
125 \ /
126 -------------------------------------------
127 Boot memory content gets transferred to
128 reserved area by firmware at the time of
129 crash
130 Fig. 1
131
132 o Memory Reservation during second kernel after crash
133
134 Low memory Top of memory
135 0 boot memory size |
136 | |<------------- Reserved dump area ----------- -->|
137 V V V
138 +-----------+----------/ /----------+---+----+-----------+----+
139 | | |CPU|HPTE| DUMP |ELF |
140 +-----------+----------/ /----------+---+----+-----------+----+
141 | |
142 V V
143 Used by second /proc/vmcore
144 kernel to boot
145 Fig. 2
146
147Currently the dump will be copied from /proc/vmcore to a
148a new file upon user intervention. The dump data available through
149/proc/vmcore will be in ELF format. Hence the existing kdump
150infrastructure (kdump scripts) to save the dump works fine with
151minor modifications.
152
153The tools to examine the dump will be same as the ones
154used for kdump.
155
156How to enable firmware-assisted dump (fadump):
157-------------------------------------
158
1591. Set config option CONFIG_FA_DUMP=y and build kernel.
1602. Boot into linux kernel with 'fadump=on' kernel cmdline option.
1613. Optionally, user can also set 'fadump_reserve_mem=' kernel cmdline
162 to specify size of the memory to reserve for boot memory dump
163 preservation.
164
165NOTE: If firmware-assisted dump fails to reserve memory then it will
166 fallback to existing kdump mechanism if 'crashkernel=' option
167 is set at kernel cmdline.
168
169Sysfs/debugfs files:
170------------
171
172Firmware-assisted dump feature uses sysfs file system to hold
173the control files and debugfs file to display memory reserved region.
174
175Here is the list of files under kernel sysfs:
176
177 /sys/kernel/fadump_enabled
178
179 This is used to display the fadump status.
180 0 = fadump is disabled
181 1 = fadump is enabled
182
183 This interface can be used by kdump init scripts to identify if
184 fadump is enabled in the kernel and act accordingly.
185
186 /sys/kernel/fadump_registered
187
188 This is used to display the fadump registration status as well
189 as to control (start/stop) the fadump registration.
190 0 = fadump is not registered.
191 1 = fadump is registered and ready to handle system crash.
192
193 To register fadump echo 1 > /sys/kernel/fadump_registered and
194 echo 0 > /sys/kernel/fadump_registered for un-register and stop the
195 fadump. Once the fadump is un-registered, the system crash will not
196 be handled and vmcore will not be captured. This interface can be
197 easily integrated with kdump service start/stop.
198
199 /sys/kernel/fadump_release_mem
200
201 This file is available only when fadump is active during
202 second kernel. This is used to release the reserved memory
203 region that are held for saving crash dump. To release the
204 reserved memory echo 1 to it:
205
206 echo 1 > /sys/kernel/fadump_release_mem
207
208 After echo 1, the content of the /sys/kernel/debug/powerpc/fadump_region
209 file will change to reflect the new memory reservations.
210
211 The existing userspace tools (kdump infrastructure) can be easily
212 enhanced to use this interface to release the memory reserved for
213 dump and continue without 2nd reboot.
214
215Here is the list of files under powerpc debugfs:
216(Assuming debugfs is mounted on /sys/kernel/debug directory.)
217
218 /sys/kernel/debug/powerpc/fadump_region
219
220 This file shows the reserved memory regions if fadump is
221 enabled otherwise this file is empty. The output format
222 is:
223 <region>: [<start>-<end>] <reserved-size> bytes, Dumped: <dump-size>
224
225 e.g.
226 Contents when fadump is registered during first kernel
227
228 # cat /sys/kernel/debug/powerpc/fadump_region
229 CPU : [0x0000006ffb0000-0x0000006fff001f] 0x40020 bytes, Dumped: 0x0
230 HPTE: [0x0000006fff0020-0x0000006fff101f] 0x1000 bytes, Dumped: 0x0
231 DUMP: [0x0000006fff1020-0x0000007fff101f] 0x10000000 bytes, Dumped: 0x0
232
233 Contents when fadump is active during second kernel
234
235 # cat /sys/kernel/debug/powerpc/fadump_region
236 CPU : [0x0000006ffb0000-0x0000006fff001f] 0x40020 bytes, Dumped: 0x40020
237 HPTE: [0x0000006fff0020-0x0000006fff101f] 0x1000 bytes, Dumped: 0x1000
238 DUMP: [0x0000006fff1020-0x0000007fff101f] 0x10000000 bytes, Dumped: 0x10000000
239 : [0x00000010000000-0x0000006ffaffff] 0x5ffb0000 bytes, Dumped: 0x5ffb0000
240
241NOTE: Please refer to Documentation/filesystems/debugfs.txt on
242 how to mount the debugfs filesystem.
243
244
245TODO:
246-----
247 o Need to come up with the better approach to find out more
248 accurate boot memory size that is required for a kernel to
249 boot successfully when booted with restricted memory.
250 o The fadump implementation introduces a fadump crash info structure
251 in the scratch area before the ELF core header. The idea of introducing
252 this structure is to pass some important crash info data to the second
253 kernel which will help second kernel to populate ELF core header with
254 correct data before it gets exported through /proc/vmcore. The current
255 design implementation does not address a possibility of introducing
256 additional fields (in future) to this structure without affecting
257 compatibility. Need to come up with the better approach to address this.
258 The possible approaches are:
259 1. Introduce version field for version tracking, bump up the version
260 whenever a new field is added to the structure in future. The version
261 field can be used to find out what fields are valid for the current
262 version of the structure.
263 2. Reserve the area of predefined size (say PAGE_SIZE) for this
264 structure and have unused area as reserved (initialized to zero)
265 for future field additions.
266 The advantage of approach 1 over 2 is we don't need to reserve extra space.
267---
268Author: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
269This document is based on the original documentation written for phyp
270assisted dump by Linas Vepstas and Manish Ahuja.
diff --git a/Documentation/powerpc/mpc52xx.txt b/Documentation/powerpc/mpc52xx.txt
index 10dd4ab93b85..0d540a31ea1a 100644
--- a/Documentation/powerpc/mpc52xx.txt
+++ b/Documentation/powerpc/mpc52xx.txt
@@ -2,7 +2,7 @@ Linux 2.6.x on MPC52xx family
2----------------------------- 2-----------------------------
3 3
4For the latest info, go to http://www.246tNt.com/mpc52xx/ 4For the latest info, go to http://www.246tNt.com/mpc52xx/
5 5
6To compile/use : 6To compile/use :
7 7
8 - U-Boot: 8 - U-Boot:
@@ -10,23 +10,23 @@ To compile/use :
10 if you wish to ). 10 if you wish to ).
11 # make lite5200_defconfig 11 # make lite5200_defconfig
12 # make uImage 12 # make uImage
13 13
14 then, on U-boot: 14 then, on U-boot:
15 => tftpboot 200000 uImage 15 => tftpboot 200000 uImage
16 => tftpboot 400000 pRamdisk 16 => tftpboot 400000 pRamdisk
17 => bootm 200000 400000 17 => bootm 200000 400000
18 18
19 - DBug: 19 - DBug:
20 # <edit Makefile to set ARCH=ppc & CROSS_COMPILE=... ( also EXTRAVERSION 20 # <edit Makefile to set ARCH=ppc & CROSS_COMPILE=... ( also EXTRAVERSION
21 if you wish to ). 21 if you wish to ).
22 # make lite5200_defconfig 22 # make lite5200_defconfig
23 # cp your_initrd.gz arch/ppc/boot/images/ramdisk.image.gz 23 # cp your_initrd.gz arch/ppc/boot/images/ramdisk.image.gz
24 # make zImage.initrd 24 # make zImage.initrd
25 # make 25 # make
26 26
27 then in DBug: 27 then in DBug:
28 DBug> dn -i zImage.initrd.lite5200 28 DBug> dn -i zImage.initrd.lite5200
29 29
30 30
31Some remarks : 31Some remarks :
32 - The port is named mpc52xxx, and config options are PPC_MPC52xx. The MGT5100 32 - The port is named mpc52xxx, and config options are PPC_MPC52xx. The MGT5100
diff --git a/Documentation/powerpc/phyp-assisted-dump.txt b/Documentation/powerpc/phyp-assisted-dump.txt
deleted file mode 100644
index ad340205d96a..000000000000
--- a/Documentation/powerpc/phyp-assisted-dump.txt
+++ /dev/null
@@ -1,127 +0,0 @@
1
2 Hypervisor-Assisted Dump
3 ------------------------
4 November 2007
5
6The goal of hypervisor-assisted dump is to enable the dump of
7a crashed system, and to do so from a fully-reset system, and
8to minimize the total elapsed time until the system is back
9in production use.
10
11As compared to kdump or other strategies, hypervisor-assisted
12dump offers several strong, practical advantages:
13
14-- Unlike kdump, the system has been reset, and loaded
15 with a fresh copy of the kernel. In particular,
16 PCI and I/O devices have been reinitialized and are
17 in a clean, consistent state.
18-- As the dump is performed, the dumped memory becomes
19 immediately available to the system for normal use.
20-- After the dump is completed, no further reboots are
21 required; the system will be fully usable, and running
22 in its normal, production mode on its normal kernel.
23
24The above can only be accomplished by coordination with,
25and assistance from the hypervisor. The procedure is
26as follows:
27
28-- When a system crashes, the hypervisor will save
29 the low 256MB of RAM to a previously registered
30 save region. It will also save system state, system
31 registers, and hardware PTE's.
32
33-- After the low 256MB area has been saved, the
34 hypervisor will reset PCI and other hardware state.
35 It will *not* clear RAM. It will then launch the
36 bootloader, as normal.
37
38-- The freshly booted kernel will notice that there
39 is a new node (ibm,dump-kernel) in the device tree,
40 indicating that there is crash data available from
41 a previous boot. It will boot into only 256MB of RAM,
42 reserving the rest of system memory.
43
44-- Userspace tools will parse /sys/kernel/release_region
45 and read /proc/vmcore to obtain the contents of memory,
46 which holds the previous crashed kernel. The userspace
47 tools may copy this info to disk, or network, nas, san,
48 iscsi, etc. as desired.
49
50 For Example: the values in /sys/kernel/release-region
51 would look something like this (address-range pairs).
52 CPU:0x177fee000-0x10000: HPTE:0x177ffe020-0x1000: /
53 DUMP:0x177fff020-0x10000000, 0x10000000-0x16F1D370A
54
55-- As the userspace tools complete saving a portion of
56 dump, they echo an offset and size to
57 /sys/kernel/release_region to release the reserved
58 memory back to general use.
59
60 An example of this is:
61 "echo 0x40000000 0x10000000 > /sys/kernel/release_region"
62 which will release 256MB at the 1GB boundary.
63
64Please note that the hypervisor-assisted dump feature
65is only available on Power6-based systems with recent
66firmware versions.
67
68Implementation details:
69----------------------
70
71During boot, a check is made to see if firmware supports
72this feature on this particular machine. If it does, then
73we check to see if a active dump is waiting for us. If yes
74then everything but 256 MB of RAM is reserved during early
75boot. This area is released once we collect a dump from user
76land scripts that are run. If there is dump data, then
77the /sys/kernel/release_region file is created, and
78the reserved memory is held.
79
80If there is no waiting dump data, then only the highest
81256MB of the ram is reserved as a scratch area. This area
82is *not* released: this region will be kept permanently
83reserved, so that it can act as a receptacle for a copy
84of the low 256MB in the case a crash does occur. See,
85however, "open issues" below, as to whether
86such a reserved region is really needed.
87
88Currently the dump will be copied from /proc/vmcore to a
89a new file upon user intervention. The starting address
90to be read and the range for each data point in provided
91in /sys/kernel/release_region.
92
93The tools to examine the dump will be same as the ones
94used for kdump.
95
96General notes:
97--------------
98Security: please note that there are potential security issues
99with any sort of dump mechanism. In particular, plaintext
100(unencrypted) data, and possibly passwords, may be present in
101the dump data. Userspace tools must take adequate precautions to
102preserve security.
103
104Open issues/ToDo:
105------------
106 o The various code paths that tell the hypervisor that a crash
107 occurred, vs. it simply being a normal reboot, should be
108 reviewed, and possibly clarified/fixed.
109
110 o Instead of using /sys/kernel, should there be a /sys/dump
111 instead? There is a dump_subsys being created by the s390 code,
112 perhaps the pseries code should use a similar layout as well.
113
114 o Is reserving a 256MB region really required? The goal of
115 reserving a 256MB scratch area is to make sure that no
116 important crash data is clobbered when the hypervisor
117 save low mem to the scratch area. But, if one could assure
118 that nothing important is located in some 256MB area, then
119 it would not need to be reserved. Something that can be
120 improved in subsequent versions.
121
122 o Still working the kdump team to integrate this with kdump,
123 some work remains but this would not affect the current
124 patches.
125
126 o Still need to write a shell script, to copy the dump away.
127 Currently I am parsing it manually.