[PATCH] ARM: kexec: fix crashkernel= handling

[Dave Young]

Hi, Russell

A long standing issue, but nobody tried to do it. Thank you for bringing up.

On 03/29/16 at 11:10am, Russell King wrote:
> When the kernel crashkernel parameter is specified with just a size, we
> are supposed to allocate a region from RAM to store the crashkernel.
> However, ARM merely reserves physical address zero with no checking
> that there is even RAM there.
> 
> Fix this by lifting similar code from x86, importing it to ARM with
> the ARM specific parameters added.
> 
> Update the kdump documentation to reflect this change.
> 
> Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
> ---
>  Documentation/kdump/kdump.txt | 13 +++----------
>  arch/arm/kernel/setup.c       | 26 ++++++++++++++++++++++++++
>  2 files changed, 29 insertions(+), 10 deletions(-)
> 
> diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
> index bc4bd5a44b88..88ff63d5fde3 100644
> --- a/Documentation/kdump/kdump.txt
> +++ b/Documentation/kdump/kdump.txt
> @@ -263,12 +263,6 @@ been removed from the machine.
>      crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset]
>      range=start-[end]
>  
> -Please note, on arm, the offset is required.
> -    crashkernel=<range1>:<size1>[,<range2>:<size2>,...]@offset
> -    range=start-[end]
> -
> -    'start' is inclusive and 'end' is exclusive.
> -
>  For example:
>  
>      crashkernel=512M-2G:64M,2G-:128M
> @@ -307,10 +301,9 @@ 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". Note that the start address of the kernel
> -   will be aligned to 128MiB (0x08000000), so if the start address is not then
> -   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 arm, the use of "crashkernel=Y at X" is no longer necessary; the
> +   kernel will automatically locate the crash kernel image within the
> +   first 512MB of RAM if X is not given.
>  
>  
>  Load the Dump-capture Kernel
> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> index 7d0cba6f1cc5..5d8511c425f0 100644
> --- a/arch/arm/kernel/setup.c
> +++ b/arch/arm/kernel/setup.c
> @@ -938,6 +938,13 @@ static int __init init_machine_late(void)
>  late_initcall(init_machine_late);
>  
>  #ifdef CONFIG_KEXEC
> +/*
> + * The crash region must be aligned to 128MB to avoid
> + * zImage relocating below the reserved region.
> + */
> +#define CRASH_ALIGN	(128 << 20)
> +#define CRASH_ADDR_MAX	(PHYS_OFFSET + (512 << 20))

Any reason to limit crash mem within the first 512M only? What if one want to
reserve memory over 512M?

Thanks
Dave