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

[Huacai Chen]

Hi, Jinyang,

On Wed, Sep 23, 2020 at 11:02 AM Jinyang He <hejinyang at loongson.cn> wrote:
>
> 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())
This seems like another story.

>
> Besides, "mem=" may be useless for kdump. Youling had submitted a patch
> about removing "mem="  serveral days ago.
kexec-tools use "mem=" to pass usable memory for the crash kernel,
Youling removes the base address of "mem=", but "mem=" is still here.

>
> For Loongson64 platform, you can try crashkernel=SIZE at 38M after fixed
> "mem=".
> 38M means 40M - 2M, 2M is needed because old firmware compatibility.
"crashkernel=" is for the normal kernel specified by BIOS, and "mem="
is for the crash kernel specified by kexec-tools.

Huacai
>
> Thanks,
> - Jinyang.
>
> >       }
> >       start = 0;
> >       size = memparse(p, &p);
>