Re: [PATCH] mips: kdump: Crash kernel should be able to see old memories

[Youling Tang]

Hi, Jiaxun

On 04/20/2021 09:11 AM, Jiaxun Yang wrote:
> 在 2021/4/19 18:56, Youling Tang 写道:
> > From: Huacai Chen <chenhc@xxxxxxxxxx>
> >
> > kexec-tools use mem=X@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 <chenhuacai@xxxxxxxxxx>
> > Signed-off-by: Youling Tang <tangyouling@xxxxxxxxxxx>
> > ---
> >   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 b86e241..ac90d3b 100644
> > --- a/arch/mips/kernel/setup.c
> > +++ b/arch/mips/kernel/setup.c
> > @@ -351,8 +351,10 @@ static int __init early_parse_mem(char *p)
> >        */
> >       if (usermem == 0) {
> >           usermem = 1;
> > +#ifndef CONFIG_CRASH_DUMP
>
> Why depend on a config instead of a runtime variable?
If not depend on config, we can determine whether the command line contains
the "elfcorehdr=" parameter, because the "mem=" and "elfcorhdr=" parameters
are automatically added in kexec-tools. So if there is an "elfcorehdr="
parameter in the command line, it means that the currently running kernel
is a capture kernel, and the memblock_remove() operation is not called.

The revised patch is as follows:
        if (usermem == 0) {
                usermem = 1;
-               memblock_remove(memblock_start_of_DRAM(),
-                       memblock_end_of_DRAM() - memblock_start_of_DRAM());
+               if (!strstr(boot_command_line, "elfcorehdr")) {
+                       memblock_remove(memblock_start_of_DRAM(),
+                               memblock_end_of_DRAM() - 
memblock_start_of_DRAM());
+               }

Do you think it is feasible?
> Btw as you are fixing my commit please keep me CCed.
Sorry, I will add your CCed.

Thanks,
Youling
> Thanks.
>
>
> - Jiaxun