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Date:   Sat, 19 Sep 2020 18:17:21 +0800
From:   Jiaxun Yang <jiaxun.yang@flygoat.com>
To:     Youling Tang <tangyouling@loongson.cn>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>
CC:     linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] MIPS: kexec: Add crashkernel=YM handling
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=E4=BA=8E 2020=E5=B9=B49=E6=9C=8819=E6=97=A5 GMT+08:00 =E4=B8=8B=E5=8D=884=
:29:39, Youling Tang <tangyouling@loongson=2Ecn> =E5=86=99=E5=88=B0:
>
>
>On 09/19/2020 03:02 PM, Jiaxun Yang wrote:
>>
>> =E4=BA=8E 2020=E5=B9=B49=E6=9C=8819=E6=97=A5 GMT+08:00 =E4=B8=8A=E5=8D=
=889:55:46, Youling Tang <tangyouling@loongson=2Ecn> =E5=86=99=E5=88=B0:
>>> When the kernel crashkernel parameter is specified with just a size,
>>> we are supposed to allocate a region from RAM to store the crashkernel=
=2E
>>> However, MIPS merely reserves physical address zero with no checking
>>> that there is even RAM there=2E
>>>
>>> Fix this by lifting similar code from x86, importing it to MIPS with t=
he
>>> MIPS specific parameters added=2E In the absence of any platform speci=
fic
>>> information, we allocate the crashkernel region from the first 512MB o=
f
>>> physical memory (limited to CKSEG0 or KSEG0 address range)=2E
>>>
>>> When X is not specified, crash_base defaults to 0 (crashkernel=3DYM@XM=
)=2E
>>>
>>> E=2Eg=2E without this patch:
>>>
>>> The environment as follows:
>>> [    0=2E000000] MIPS: machine is loongson,loongson64c-4core-ls7a
>>> =2E=2E=2E
>>> [    0=2E000000] Kernel command line: root=3D/dev/sda2 crashkernel=3D9=
6M =2E=2E=2E
>>>
>>> The warning as follows:
>>> [    0=2E000000] Invalid memory region reserved for crash kernel
>>>
>>> And the iomem as follows:
>>> 00200000-0effffff : System RAM
>>>   00200000-00b47f87 : Kernel code
>>>   00b47f88-00dfffff : Kernel data
>>>   00e60000-01f73c7f : Kernel bss
>>> 1a000000-1bffffff : pci@1a000000
>>> =2E=2E=2E
>>>
>>> With this patch:
>>>
>>> After increasing crash_base <=3D 0 handling=2E
>>>
>>> And the iomem as follows:
>>> 00200000-0effffff : System RAM
>>>   00200000-00b47f87 : Kernel code
>>>   00b47f88-00dfffff : Kernel data
>>>   00e60000-01f73c7f : Kernel bss
>>>   04000000-09ffffff : Crash kernel
>>> 1a000000-1bffffff : pci@1a000000
>>> =2E=2E=2E
>>>
>>> Signed-off-by: Youling Tang <tangyouling@loongson=2Ecn>
>>> ---
>>> arch/mips/kernel/setup=2Ec | 24 +++++++++++++++++++++---
>>> 1 file changed, 21 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/arch/mips/kernel/setup=2Ec b/arch/mips/kernel/setup=2Ec
>>> index bf5f5ac=2E=2E59a88ea 100644
>>> --- a/arch/mips/kernel/setup=2Ec
>>> +++ b/arch/mips/kernel/setup=2Ec
>>> @@ -477,6 +477,11 @@ early_param("elfcorehdr", early_parse_elfcorehdr)=
;
>>> #endif
>>>
>>> #ifdef CONFIG_KEXEC
>>> +
>>> +/* 64M alignment for crash kernel regions */
>>> +#define CRASH_ALIGN	SZ_64M
>>> +#define CRASH_ADDR_MAX	SZ_512M
>> Hi Youling
>>
>> How do you determine the alignment requirement?
>>
>> Can we relax it?
>>
>> Thanks=2E
>>
>> - Jiaxun
>Hi Jiaxun
>
>Only when XM is not specified, 64M alignment is specified=2E
>
>After the capture kernel is configured with CRASH_DUMP, PHYSICAL_START
>defaults to 0x0xffffffff84000000 (64M)=2E The kexec -p operation will
>succeed only when the reserved Crash kernel start address is consistent
>with PHYSICAL_START=2E
>
>The description of PHYSICAL_START in arch/mips/Kconfig:2996 is as follows=
:
>This gives the CKSEG0 or KSEG0 address where the kernel is loaded=2EIf yo=
u
>plan to use kernel for capturing the crash dump change this value to star=
t
>of the reserved region (the "X" value as specified in the=20
>"crashkernel=3DYM@XM"
>command line boot parameter passed to the panic-ed kernel)=2E

Thanks for your explanation~

That makes sense=2E

- Jiaxun


>
>Thanks,
>
>- Youling

[=2E=2E=2E]