[PATCH] ARM: Add arm description to Documentation/kdump/kdump.txt

[Vivek Goyal]

On Thu, Jul 31, 2014 at 02:03:31PM +0800, HuKeping wrote:
> Add arm specific parts to kdump kernel documentation.
> 

Hi Hu,

So kexec on arm (32bit) now works? All the kernel pieces and kexec-tools
pieces are upstream? (Sorry, I have not been able to keeptrack of arm
development).


> ----------------------------------------
> Signed-off-by: Hu Keping <hukeping at huawei.com>
> ---
>  Documentation/kdump/kdump.txt | 25 ++++++++++++++++++++++---
>  1 file changed, 22 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
> index 88d5a86..5fc98d6 100644
> --- a/Documentation/kdump/kdump.txt
> +++ b/Documentation/kdump/kdump.txt
> @@ -18,7 +18,7 @@ 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, ia64,
> -and s390x architectures.
> +s390x and arm 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
> @@ -112,7 +112,7 @@ There are two possible methods of using Kdump.
>  2) Or use the system kernel binary itself as dump-capture kernel and there is
>     no need to build a separate dump-capture kernel. This is possible
>     only with the architectures which support a relocatable kernel. As
> -   of today, i386, x86_64, ppc64 and ia64 architectures support relocatable
> +   of today, i386, x86_64, ppc64, ia64 and arm architectures support relocatable
>     kernel.

So zImage is relocatable on arm?

>  
>  Building a relocatable kernel is advantageous from the point of view that
> @@ -296,6 +296,12 @@ Boot into System Kernel
>     on the memory consumption of the kdump system. In general this is not
>     dependent on the memory size of the production system.
>  
> +   On arm, use "crashkernel=Y at X".

Do you support other forms of crashkernel= parameter? Like crashkernel=X.
A longer list of parameters is available in kernel-parameters.txt.

> Note that the start address of the kernel
> +   will be aligned to 128MiB (0x08000000),

x86 kernel is 2MB aligned. 128MB aligned seems to be huge. Where does
that restriction come from.

>so if the start address is not then
> +   any space blow the alignment point may be overwrited by the dump-caputre kernel,
> +   which means it is possible that the vmcore is not that precise as expected.

What does above statement mean? I think it requires some work. And also
some examples of what's a reasonable crashkernel=X at Y values for arm.


> +
> +
>  Load the Dump-capture Kernel
>  ============================
>  
> @@ -315,7 +321,8 @@ For ia64:
>  	- Use vmlinux or vmlinuz.gz
>  For s390x:
>  	- Use image or bzImage
> -
> +For arm:
> +	- Use zImage
>  
>  If you are using a uncompressed vmlinux image then use following command
>  to load dump-capture kernel.
> @@ -331,6 +338,15 @@ to load dump-capture kernel.
>     --initrd=<initrd-for-dump-capture-kernel> \
>     --append="root=<root-dev> <arch-specific-options>"
>  
> +If you are using a compressed zImage, then use following command
> +to load dump-capture kernel.
> +
> +   kexec --type zImage -p <dump-capture-kernel-bzImage> \
> +   --initrd=<initrd-for-dump-capture-kernel> \
> +   --dtb=<dtb-for-dump-capture-kernel> \
> +   --append="root=<root-dev> <arch-specific-options>"
> +
> +
>  Please note, that --args-linux does not need to be specified for ia64.
>  It is planned to make this a no-op on that architecture, but for now
>  it should be omitted
> @@ -347,6 +363,9 @@ For ppc64:
>  For s390x:
>  	"1 maxcpus=1 cgroup_disable=memory"
>  
> +For arm:
> +	"1 maxcpus=1 reset_devices"
> +

nr_cpus=1 does not work on arm? We prefer that over maxcpus=1.

Thanks
Vivek