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Commit 91302143 authored by Michael Holzheu's avatar Michael Holzheu Committed by Martin Schwidefsky
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[S390] Add s390x description to Documentation/kdump/kdump.txt 



Add s390x specific parts to kdump kernel documentation.

Signed-off-by: default avatarMichael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 7fe7a18c

Documentation/kdump/kdump.txt

+32 −3
Original line number Diff line number Diff line
@@ -17,8 +17,8 @@ You can use common commands, such as cp and scp, to copy the 
memory image to a dump file on the local disk, or across the network to

a remote system.



Kdump and kexec are currently supported on the x86, x86_64, ppc64 and ia64

architectures.

Kdump and kexec are currently supported on the x86, x86_64, ppc64, ia64,

and s390x architectures.



When the system kernel boots, it reserves a small section of memory for

the dump-capture kernel. This ensures that ongoing Direct Memory Access
@@ -34,11 +34,18 @@ Similarly on PPC64 machines first 32KB of physical memory is needed for 
booting regardless of where the kernel is loaded and to support 64K page

size kexec backs up the first 64KB memory.



For s390x, when kdump is triggered, the crashkernel region is exchanged

with the region [0, crashkernel region size] and then the kdump kernel

runs in [0, crashkernel region size]. Therefore no relocatable kernel is

needed for s390x.



All of the necessary information about the system kernel's core image is

encoded in the ELF format, and stored in a reserved area of memory

before a crash. The physical address of the start of the ELF header is

passed to the dump-capture kernel through the elfcorehdr= boot

parameter.

parameter. Optionally the size of the ELF header can also be passed

when using the elfcorehdr=[size[KMG]@]offset[KMG] syntax.





With the dump-capture kernel, you can access the memory image, or "old

memory," in two ways:
@@ -291,6 +298,10 @@ Boot into System Kernel 
   The region may be automatically placed on ia64, see the

   dump-capture kernel config option notes above.



   On s390x, typically use "crashkernel=xxM". The value of xx is dependent

   on the memory consumption of the kdump system. In general this is not

   dependent on the memory size of the production system.



Load the Dump-capture Kernel

============================
@@ -308,6 +319,8 @@ For ppc64: 
	- Use vmlinux

For ia64:

	- Use vmlinux or vmlinuz.gz

For s390x:

	- Use image or bzImage





If you are using a uncompressed vmlinux image then use following command
@@ -337,6 +350,8 @@ For i386, x86_64 and ia64: 
For ppc64:

	"1 maxcpus=1 noirqdistrib reset_devices"



For s390x:

	"1 maxcpus=1 cgroup_disable=memory"



Notes on loading the dump-capture kernel:
@@ -362,6 +377,20 @@ Notes on loading the dump-capture kernel: 
  dump. Hence generally it is useful either to build a UP dump-capture

  kernel or specify maxcpus=1 option while loading dump-capture kernel.



* For s390x there are two kdump modes: If a ELF header is specified with

  the elfcorehdr= kernel parameter, it is used by the kdump kernel as it

  is done on all other architectures. If no elfcorehdr= kernel parameter is

  specified, the s390x kdump kernel dynamically creates the header. The

  second mode has the advantage that for CPU and memory hotplug, kdump has

  not to be reloaded with kexec_load().



* For s390x systems with many attached devices the "cio_ignore" kernel

  parameter should be used for the kdump kernel in order to prevent allocation

  of kernel memory for devices that are not relevant for kdump. The same

  applies to systems that use SCSI/FCP devices. In that case the

  "allow_lun_scan" zfcp module parameter should be set to zero before

  setting FCP devices online.



Kernel Panic

============