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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [patch] kexec and kdump documentation for xen
Add guide to using the kexec and kdump facility in xen. Signed-off-by: Simon Horman <horms@xxxxxxxxxxxx> --- I the work on this document using an ia64 machine and qemu emulating x86_32. I am yet to verify it on x86_32 hardware or x86_64. Index: xen-unstable.hg/docs/misc/kexec_and_kdump.txt =================================================================== --- /dev/null 1970-01-01 00:00:00.000000000 +0000 +++ xen-unstable.hg/docs/misc/kexec_and_kdump.txt 2008-08-12 00:11:45.000000000 +1000 @@ -0,0 +1,213 @@ + +======================= +Kexec and Kdump for Xen +======================= + +This is a breif guide to using Kexec and Kdump in conjunction with Xen. +This functionaly works at the level of the hypervisor and dom0 kernel. +And will thus affect all guests running on a machine. + +At this stage it does not work in conjunction with domU kernels. + +This document should be read in conjunction with +Documentation/kdump/kdump.txt from the Linux kernel source. +Some of the information in this document has been +sourced from that document. + + +Kexec +===== + +It is possible to kexec from Xen or Linux to either Xen or Linux. + +Pattern | Before Kexec | After Kexec +---------------+--------------------+-------------------- +Xen -> Xen | first hypervisor & | second hypervisor & + | dom0 kernel | dom0 kernel +---------------+--------------------+-------------------- +Xen -> Linux | first hypervisor & | second kernel + | dom0 kernel | +---------------+--------------------+-------------------- +Linux -> Xen | first kernel | second hypervisor & + | | dom0 kernel +---------------+--------------------+-------------------- +Linux -> Linux | first kernel | second kernel + +If you are kexecing to Xen then you will also need to preapare the second +hypervisor and dom0 kernel that will run after kexec. These may be the same +as the first hypervisor and dom0 kernel that are used before kexec if you +are kexecing from Xen to Xen. + +If you are kexecing to Linux then you will need to prepare the second Linux +kernel that will run after kexec. In the case that you are kexecing from +Linux, it may be the same as the first kernel image that that runs before +kexec. + +Regardless of which kexec pattern you wish to run, you will +need to have kexec-tools installed. This provides the kexec command. + +1. Load +------- + +Before kexecing the second kernel or hypervisor & dom0 kernel +need to be loaded into the running hypervisor or kernel using +the kexec command. + + a. To kexec to Xen (Xen->Xen or Linux->Xen) + + kexec -l --append="XEN_ARGS -- DOM0_ARGS" \ + --vmm="XEN_IMAGE" "DOM0_IMAGE" KEXEC_ARGS + + where: + XEN_ARGS: command line arguments to the xen hypervisor + On x86 the no-real-mode argument should be included + DOM0_ARGS: command line arguments to the dom0 kernel + XEN_IMAGE: xen hypervisor image + DOM0_IMAGE: dom0 kernel image + KEXEC_ARGS: additional kexec-tools command line arguments + + e.g. kexec -l --append "no-real-mode" --vmm="/boot/xen.gz" /boot/vmlinuz.gz + + OR + + b. To kexec to Linux (Xen->Linux or Linux->Linux) + + kexec -l LINUX_IMAGE --append "$LINUX_ARGS" KEXEC_ARGS + + where: + LINUX_IMAGE: the second linux kernel image + LINUX_ARGS: command line arguments to the second linux kernel + KEXEC_ARGS: additional kexec-tools command line arguments + + e.g. kexec -l /boot/second-vmlinuz.gz + +2. Execute +---------- + +Once the second kernel is loaded, it can be executed at any time. +If you don't see the second kernel booting within a second or so, +you are in trouble :( + + kexec -e + +Kdump +===== + +It is possible to kdump from Xen or Linux to a Linux crash kernel. +It is not possible to use xen as a crash kernel. + +Pattern | Before Kexec | After Kexec +---------------+--------------------+-------------------- +Xen -> Linux | first hypervisor & | crash kernel + | dom0 kernel | +---------------+--------------------+-------------------- +Linux -> Linux | first kernel | crash kernel + +Regardless of if you are kdumping from Xen or Linux you will need to +prepare a linux crash kernel. You will also need to have kexec-tools +installed. This provides the kexec command. + +0. Set-Up The Crash Kernel Region +--------------------------------- + +In order to use kdump an area of memory has to be reserved at boot time. +This is the area of memory that the crash kernel will use, thus allowing it +to run without disrupting the memory used by the first kernel. This area is +called the crash kernel region and is reserved using the crashkernel +command line parameter to the Xen hypervisor. It has two forms: + + i) crashkernel=size + + This is the simplest and recommended way to reserve the crash kernel + region. Just specify how large the region should be and the hypervisor + will find a good location for it. A good size to start with is 128Mb + + e.g. + + crashkernel=128M + + ii) crashkernel=size@base + + In this form the base address is provided in addition to + the size. Use this if auto-placement doesn't work for some reason. + It is strongly recommended that the base address be aligned + to 64Mb, else memory below the alignment point will not + be usable. + + e.g. crashkernel=128M@256M + + Regardless of which of the two forms of the crashkernel command line you + use, the crash kernel region should appear in /proc/iomem on x86 or + /proc/iomem_machine on ia64. If it doesn't then either the crashkernel + parameter is missing, or for some reason the region couldn't be placed - + for instance because it is too large. + + # cat /proc/iomem + ... + 00100000-07feffff : System RAM + 00100000-00bfffff : Hypervisor code and data + 0533f000-0733efff : Crash kernel + ... + + +1. Load +------- + +Once you are running in a kexec-enabled hypervisor and dom0, +you can prepare to kdump by loading the crash kernel into the +running kernel. + + kexec -p CRASH_KERNEL_IMAGE --append "$CRASH_KERNEL_ARGS" KEXEC_ARGS + + where: + CRASH_KERNEL_IMAGE: the crash kernel image + CRASH_KERNEL_ARGS: command line arguments to the crash kernel + init 1 is strongly recommended + irqpoll is strongly recommended + maxcpus=1 is required if the crash kernel is SMP + reset_devices is strongly recommended + KEXEC_ARGS: additional kexec-tools command line arguments + On x86 --args-linux should be supplied if an uncompressed + vmlinux image is used as the crash kernel + + e.g. kexec -p /boot/crash-vmlinuz \ + --append "init 1 irqpoll maxcpus=1 reset_devices" --args-linux + +On x86 systems the crash kernel may be either +- A uncompressed vmlinux image if the kernel is not relocatable +- A compressed bzImage or vmlinuz image if the kernel is relocatable +- Relocatability is crontroled by the CONFIG_RELOCATABLE kernel + compile configuration parameter. This option may not be available + depending on the kernel version +On ia64 + Either a vmlinuz or vmlinux.gz image may be used + + +2. Execute +---------- + +Once the second kernel is loaded, the crash kernel will be executed if the +hypervisor panics. It will also be executed if dom0 panics or if dom0 +oopses and /proc/sys/kernel/panic_on_oops is set to a non-zero value + +echo 1 > /proc/sys/kernel/panic_on_oops + +Kdump may also be triggered (for testing) + + a. From Domain 0 + + echo c > /proc/sysrq-trigger + + b. From Xen + + Enter the xen console + + ctrl^a ctrl^a (may be bound to a different key, this is the default) + + Select C for "trigger a crashdump" + + C + +If you don't see the crash kernel booting within a second or so, +you are in trouble :( + _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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