linux-kernel - Re: [v2 1/5] arm64: kdump: reserve memory for crash dump kernel

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Message-ID: <55505C91.8070503@linaro.org>
Date:	Mon, 11 May 2015 16:38:57 +0900
From:	AKASHI Takahiro <takahiro.akashi@...aro.org>
To:	Baoquan He <bhe@...hat.com>
CC:	catalin.marinas@....com, will.deacon@....com, vgoyal@...hat.com,
	hbabus@...ibm.com, geoff@...radead.org, broonie@...nel.org,
	david.griego@...aro.org, kexec@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org, linux-kernel@...r.kernel.org
Subject: Re: [v2 1/5] arm64: kdump: reserve memory for crash dump kernel

Hi Baoquan,

On 04/28/2015 06:19 PM, Baoquan He wrote:
>> +#ifdef CONFIG_CRASH_DUMP
>> +/*
>> + * reserve_elfcorehdr() - reserves memory for elf core header
>> + *
>> + * This function reserves memory area given in "elfcorehdr=" kernel command
>> + * line parameter. The memory reserved is used by a dump capture kernel to
>> + * identify the memory used by primary kernel.
>> + */
>
> Hi AKASHI,
>
> May I know why elfcorehdr need be reserved separately but not locate a
> memory region in crashkernel reserved region like all other ARCHs? Is
> there any special reason?

I don't get your point, but arm as well as arm64 locates elfcorehdr
in a crash kernel's memory region.
See kexec/arch/arm{,64}/crashdump-arm{,64}.c in kexec-tools.

And this region is reserved at boot time *on crash kernel* because we don't want
to corrupt it accidentally.
(After Mark's comment, we might better remove the mmu mapping for this region, too.)


Make sense?

-Takahiro AKASHI

> Thanks
> Baoquan
>
>> +static void __init reserve_elfcorehdr(void)
>> +{
>> +	if (!elfcorehdr_size)
>> +		return;
>> +
>> +	if (memblock_is_region_reserved(elfcorehdr_addr, elfcorehdr_size)) {
>> +		pr_warn("elfcorehdr reservation failed - memory is in use (0x%llx)\n",
>> +			elfcorehdr_addr);
>> +		return;
>> +	}
>> +
>> +	if (memblock_reserve(elfcorehdr_addr, elfcorehdr_size)) {
>> +		pr_warn("elfcorehdr reservation failed - out of memory\n");
>> +		return;
>> +	}
>> +
>> +	pr_info("Reserving %lldKB of memory at %lldMB for elfcorehdr\n",
>> +		elfcorehdr_size >> 10, elfcorehdr_addr >> 20);
>> +}
>> +#endif /* CONFIG_CRASH_DUMP */
>>   /*
>>    * Return the maximum physical address for ZONE_DMA (DMA_BIT_MASK(32)). It
>>    * currently assumes that for memory starting above 4G, 32-bit devices will
>> @@ -170,6 +247,13 @@ void __init arm64_memblock_init(void)
>>   		memblock_reserve(__virt_to_phys(initrd_start), initrd_end - initrd_start);
>>   #endif
>>
>> +#ifdef CONFIG_KEXEC
>> +	reserve_crashkernel(memory_limit);
>> +#endif
>> +#ifdef CONFIG_CRASH_DUMP
>> +	reserve_elfcorehdr();
>> +#endif
>> +
>>   	early_init_fdt_scan_reserved_mem();
>>
>>   	/* 4GB maximum for 32-bit only capable devices */
>> --
>> 1.7.9.5
>>
>> --
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