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| -rw-r--r-- | Documentation/powerpc/phyp-assisted-dump.txt | 127 |
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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 @@ - - Hypervisor-Assisted Dump - ------------------------ - November 2007 - -The goal of hypervisor-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. - -As compared to kdump or other strategies, hypervisor-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. --- As the dump is performed, the dumped memory becomes - immediately available to the system for normal use. --- After the dump is completed, no further reboots are - required; the system will be fully usable, and running - in its normal, production mode on its normal kernel. - -The above can only be accomplished by coordination with, -and assistance from the hypervisor. The procedure is -as follows: - --- When a system crashes, the hypervisor will save - the low 256MB of RAM to a previously registered - save region. It will also save system state, system - registers, and hardware PTE's. - --- After the low 256MB area has been saved, the - hypervisor will reset PCI and other hardware state. - It will *not* clear 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 there is crash data available from - a previous boot. It will boot into only 256MB of RAM, - reserving the rest of system memory. - --- Userspace tools will parse /sys/kernel/release_region - and read /proc/vmcore to obtain the contents of memory, - which holds the previous crashed kernel. The userspace - tools may copy this info to disk, or network, nas, san, - iscsi, etc. as desired. - - For Example: the values in /sys/kernel/release-region - would look something like this (address-range pairs). - CPU:0x177fee000-0x10000: HPTE:0x177ffe020-0x1000: / - DUMP:0x177fff020-0x10000000, 0x10000000-0x16F1D370A - --- As the userspace tools complete saving a portion of - dump, they echo an offset and size to - /sys/kernel/release_region to release the reserved - memory back to general use. - - An example of this is: - "echo 0x40000000 0x10000000 > /sys/kernel/release_region" - which will release 256MB at the 1GB boundary. - -Please note that the hypervisor-assisted dump feature -is only available on Power6-based systems with recent -firmware versions. - -Implementation details: ----------------------- - -During boot, a check is made to see if firmware supports -this feature on this particular machine. If it does, then -we check to see if a active dump is waiting for us. If yes -then everything but 256 MB of RAM is reserved during early -boot. This area is released once we collect a dump from user -land scripts that are run. If there is dump data, then -the /sys/kernel/release_region file is created, and -the reserved memory is held. - -If there is no waiting dump data, then only the highest -256MB of the ram is reserved as a scratch area. 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 low 256MB in the case a crash does occur. See, -however, "open issues" below, as to whether -such a reserved region is really needed. - -Currently the dump will be copied from /proc/vmcore to a -a new file upon user intervention. The starting address -to be read and the range for each data point in provided -in /sys/kernel/release_region. - -The tools to examine the dump will be same as the ones -used for kdump. - -General notes: --------------- -Security: please note that there are potential security issues -with any sort of dump mechanism. In particular, plaintext -(unencrypted) data, and possibly passwords, may be present in -the dump data. Userspace tools must take adequate precautions to -preserve security. - -Open issues/ToDo: ------------- - o The various code paths that tell the hypervisor that a crash - occurred, vs. it simply being a normal reboot, should be - reviewed, and possibly clarified/fixed. - - o Instead of using /sys/kernel, should there be a /sys/dump - instead? There is a dump_subsys being created by the s390 code, - perhaps the pseries code should use a similar layout as well. - - o Is reserving a 256MB region really required? The goal of - reserving a 256MB scratch area is to make sure that no - important crash data is clobbered when the hypervisor - save low mem to the scratch area. But, if one could assure - that nothing important is located in some 256MB area, then - it would not need to be reserved. Something that can be - improved in subsequent versions. - - o Still working the kdump team to integrate this with kdump, - some work remains but this would not affect the current - patches. - - o Still need to write a shell script, to copy the dump away. - Currently I am parsing it manually. |