Message-ID: <55505C91.8070503@linaro.org>
Date: Mon, 11 May 2015 16:38:57 +0900
From: AKASHI Takahiro <takahiro.akashi@linaro.org>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0
MIME-Version: 1.0
To: Baoquan He <bhe@redhat.com>
CC: catalin.marinas@arm.com, will.deacon@arm.com, vgoyal@redhat.com,
        hbabus@us.ibm.com, geoff@infradead.org, broonie@kernel.org,
        david.griego@linaro.org, kexec@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org, linaro-kernel@lists.linaro.org,
        linux-kernel@vger.kernel.org
Subject: Re: [v2 1/5] arm64: kdump: reserve memory for crash dump kernel
References: <1429861989-8417-1-git-send-email-takahiro.akashi@linaro.org> <1429861989-8417-2-git-send-email-takahiro.akashi@linaro.org> <20150428091935.GJ15033@dhcp-16-116.nay.redhat.com>
In-Reply-To: <20150428091935.GJ15033@dhcp-16-116.nay.redhat.com>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2708
Lines: 84

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
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>> Please read the FAQ at  http://www.tux.org/lkml/
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/