[PATCH 1/3] MIPS: Crash kernel should be able to see old memories

[Jinyang He]

On 09/23/2020 10:30 AM, Huacai Chen wrote:
> Kexec-tools use mem=X at Y to pass usable memories to crash kernel, but in
> commit a94e4f24ec836c8984f83959 ("MIPS: init: Drop boot_mem_map") all
> BIOS passed memories are removed by early_parse_mem(). I think this is
> reasonable for a normal kernel but not for a crash kernel, because a
> crash kernel should be able to see all old memories, even though it is
> not supposed to use them.
>
> Fixes: a94e4f24ec836c8984f83959 ("MIPS: init: Drop boot_mem_map")
> Signed-off-by: Huacai Chen <chenhc at lemote.com>
> ---
>   arch/mips/kernel/setup.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
> index 4c04a86..e2804a2 100644
> --- a/arch/mips/kernel/setup.c
> +++ b/arch/mips/kernel/setup.c
> @@ -392,8 +392,10 @@ static int __init early_parse_mem(char *p)
>   	 */
>   	if (usermem == 0) {
>   		usermem = 1;
> +#ifndef CONFIG_CRASH_DUMP
>   		memblock_remove(memblock_start_of_DRAM(),
>   			memblock_end_of_DRAM() - memblock_start_of_DRAM());
> +#endif

Hi, Huacai,

For this patch, I knew something what had happened. "mem=" parsing
works wrong for Loongson64. You can referenced the follow patch:
https://patchwork.kernel.org/patch/11789555/

memblock_add() calls memblock_add_range(,,, MAX_NUMNODES,)
For Loongson64 enabling NUMA, we need memblock_add_node(). (Or
using memblock_set_node() after memblock_add())

Besides, "mem=" may be useless for kdump. Youling had submitted a patch
about removing "mem="  serveral days ago.

For Loongson64 platform, you can try crashkernel=SIZE at 38M after fixed 
"mem=".
38M means 40M - 2M, 2M is needed because old firmware compatibility.

Thanks,
- Jinyang.

>   	}
>   	start = 0;
>   	size = memparse(p, &p);