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Subject: Re: [PATCH] mips: kernel: setup: fix crash kernel resource allocation
To:     Ivan Khoronzhuk <ikhoronz@cisco.com>, linux-mips@vger.kernel.org,
        tsbogend@alpha.franken.de, linux-kernel@vger.kernel.org
References: <20210206125940.111766-1-ikhoronz@cisco.com>
Cc:     yangtiezhu@loongson.cn, rppt@kernel.org, ivan.khoronzhuk@gmail.com
From:   Jinyang He <hejinyang@loongson.cn>
Message-ID: <01729c08-c5e3-e9c0-2ddb-a5289e536153@loongson.cn>
Date:   Sun, 7 Feb 2021 11:19:03 +0800
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On 02/06/2021 08:59 PM, Ivan Khoronzhuk wrote:

> In order to avoid crash kernel corruption, its memory is reserved
> early in memblock and as result, in time when resources are inited
> it's not present in memblock.memory, so crash kernel memory is out
> of ranges listed with for_each_mem_range(). To avoid it and still
> keep memory reserved lets reseve it out of loop by inserting it in
> iomem_resource.

Hi, Ivan,

I'm not familiar with memblock. If the following my ideas show my
ignorance, please forgive me.

First, not only the crash kernel is reserved early in memblock, but also
code, data, and bss are also reserved in bootmem_init():

     /* Reserve memory occupied by kernel. */
     memblock_reserve(__pa_symbol(&_text),
             __pa_symbol(&_end) - __pa_symbol(&_text));

(CONFIG_NUMA is not enabled. NUMA platform reserved them is earlier.)

If there is something unsuitable with the crash kernel, is there something
unsuitable with the kernel memory?


Then, for_each_mem_range() is normal memory. Although memblock_reserve()
has used before that, it just adds memory to memblock.reserved. That means
it will still appear in memblock.memory. Thus, here I have a question,
do we need to use replace for_each_mem_range with for_each_mem_range_rev?

Finally, thank you for the patch, it makes me think a lot.

Thanks,
Jinyang

> Fixes: a94e4f24ec83 ("MIPS: init: Drop boot_mem_map")
> Signed-off-by: Ivan Khoronzhuk <ikhoronz@cisco.com>
> ---
> Based on linux-next/master
>
>   arch/mips/kernel/setup.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
> index 3785c72bc3bc..25e376ef2f2a 100644
> --- a/arch/mips/kernel/setup.c
> +++ b/arch/mips/kernel/setup.c
> @@ -473,14 +473,15 @@ static void __init mips_parse_crashkernel(void)
>   	crashk_res.end	 = crash_base + crash_size - 1;
>   }
>   
> -static void __init request_crashkernel(struct resource *res)
> +static void __init request_crashkernel(void)
>   {
>   	int ret;
>   
>   	if (crashk_res.start == crashk_res.end)
>   		return;
>   
> -	ret = request_resource(res, &crashk_res);
> +	/* The crashk resource shoud be located in normal mem */
> +	ret = insert_resource(&iomem_resource, &crashk_res);
>   	if (!ret)
>   		pr_info("Reserving %ldMB of memory at %ldMB for crashkernel\n",
>   			(unsigned long)(resource_size(&crashk_res) >> 20),
> @@ -734,8 +735,9 @@ static void __init resource_init(void)
>   		request_resource(res, &code_resource);
>   		request_resource(res, &data_resource);
>   		request_resource(res, &bss_resource);
> -		request_crashkernel(res);
>   	}
> +
> +	request_crashkernel();
>   }
>   
>   #ifdef CONFIG_SMP