Re: [PATCH 18/19] arm64: kdump: update a kernel doc

[Mark Rutland <mark.rutland@arm.com>]

On Fri, Jan 15, 2016 at 07:18:38PM +0000, Geoff Levand wrote:
> From: AKASHI Takahiro <takahiro.akashi@linaro.org>
> 
> This patch adds arch specific descriptions about kdump usage on arm64
> to kdump.txt.
> 
> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> ---
>  Documentation/kdump/kdump.txt | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
> index bc4bd5a..36cf978 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,
> -s390x and arm architectures.
> +s390x, arm and arm64 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
> @@ -249,6 +249,20 @@ Dump-capture kernel config options (Arch Dependent, arm)
>  
>      AUTO_ZRELADDR=y
>  
> +Dump-capture kernel config options (Arch Dependent, arm64)
> +----------------------------------------------------------
> +
> +1) The maximum memory size on the dump-capture kernel must be limited by
> +   specifying:
> +
> +   mem=X[MG]
> +
> +   where X should be less than or equal to the size in "crashkernel="
> +   boot parameter. Kexec-tools will automatically add this.


This is extremely fragile, and will trivially fail when the kernel can
be loaded anywhere (see [1]).

We must explicitly describe the set of regions the crash kernel may use
(i.e. we need base and size). NAK in the absence of that.

Thanks,
Mark.

> +
> +2) Currently, kvm will not be enabled on the dump-capture kernel even
> +   if it is configured.
> +
>  Extended crashkernel syntax
>  ===========================
>  
> @@ -312,6 +326,8 @@ Boot into System Kernel
>     any space below the alignment point may be overwritten by the dump-capture kernel,
>     which means it is possible that the vmcore is not that precise as expected.
>  
> +   On arm64, use "crashkernel=Y[@X]".  Note that the start address of
> +   the kernel, X if explicitly specified, must be aligned to 2MiB (0x200000).
>  
>  Load the Dump-capture Kernel
>  ============================
> @@ -334,6 +350,8 @@ For s390x:
>  	- Use image or bzImage
>  For arm:
>  	- Use zImage
> +For arm64:
> +	- Use vmlinux or Image
>  
>  If you are using a uncompressed vmlinux image then use following command
>  to load dump-capture kernel.
> @@ -377,6 +395,9 @@ For s390x:
>  For arm:
>  	"1 maxcpus=1 reset_devices"
>  
> +For arm64:
> +	"1 mem=X[MG] maxcpus=1 reset_devices"
> +
>  Notes on loading the dump-capture kernel:
>  
>  * By default, the ELF headers are stored in ELF64 format to support
> -- 
> 2.5.0
> 
> 

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-January/398527.html

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