Re: [PATCH v15 15/20] arm64: kdump: reserve memory for crash dump kernel

[AKASHI Takahiro <takahiro.akashi@linaro.org>]

On 03/31/2016 02:19 PM, AKASHI Takahiro wrote:
> On Fri, Mar 18, 2016 at 06:08:30PM +0000, James Morse wrote:
>> Hi!
>>
>> On 14/03/16 17:48, Geoff Levand wrote:
>>> From: AKASHI Takahiro <takahiro.akashi@linaro.org>
>>>
>>> On the startup of primary kernel, the memory region used by crash dump
>>> kernel must be specified by "crashkernel=" kernel parameter.
>>> reserve_crashkernel() will allocate and reserve the region for later use.
>>>
>>> User space tools, like kexec-tools, will be able to find that region marked
>>> as "Crash kernel" in /proc/iomem.
>>
>> [NB: Re-ordered diff hunks ]
>>
>>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>>> index 7802f21..4edf181 100644
>>> --- a/arch/arm64/mm/init.c
>>> +++ b/arch/arm64/mm/init.c
>>> @@ -171,6 +229,8 @@ void __init arm64_memblock_init(void)
>>>   		memblock_reserve(__virt_to_phys(initrd_start), initrd_end - initrd_start);
>>>   #endif
>>>
>>> +	reserve_crashkernel();
>>> +
>>>   	early_init_fdt_scan_reserved_mem();
>>>
>>>   	/* 4GB maximum for 32-bit only capable devices */
>>>
>>
>>
>> This is 'nit' territory, but if you were to make this:
>>> 	if (IS_ENABLED(CONFIG_KEXEC_CORE))
>>> 		reserve_crashkernel();
>>
>> then the #ifdefs around reserve_crashkernel() can go, and the compiler will work
>> out that this static function can be optimised out. It also means the
>> compiler performs its checks, even if CONFIG_KEXEC_CORE isn't selected. The same
>> trick can be applied in patch 18 (around reserve_elfcorehdr()).
> 
> It will also make the code more understandable.

I tried this change, but
unfortunately, preserve_crashkernel() calls an external function, parse_crashkernel(),
which is defined only if CONFIG_KEXEC_CORE. So we will see a compiler error in !CONFIG_KEXEC_CORE
if we take #ifdef out around perserve_crashkernel().

-Takahiro AKASHI


> Thanks,
> -Takahiro AKASHI
> 
>>> @@ -66,6 +67,63 @@ static int __init early_initrd(char *p)
>>>   early_param("initrd", early_initrd);
>>>   #endif
>>>   
>>> +#ifdef CONFIG_KEXEC_CORE
>>> +/*
>>> + * reserve_crashkernel() - reserves memory for crash kernel
>>> + *
>>> + * This function reserves memory area given in "crashkernel=" kernel command
>>> + * line parameter. The memory reserved is used by dump capture kernel when
>>> + * primary kernel is crashing.
>>> + */
>>> +static void __init reserve_crashkernel(void)
>>> +{
>>> +	unsigned long long crash_size = 0, crash_base = 0;
>>> +	int ret;
>>> +
>>> +	ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
>>> +				&crash_size, &crash_base);
>>> +	if (ret)
>>> +		return;
>>> +
>>> +	if (crash_base == 0) {
>>> +		crash_base = memblock_find_in_range(0,
>>> +				MEMBLOCK_ALLOC_ACCESSIBLE, crash_size, 1 << 21);
>>> +		if (crash_base == 0) {
>>> +			pr_warn("Unable to allocate crashkernel (size:%llx)\n",
>>> +				crash_size);
>>> +			return;
>>> +		}
>>> +		memblock_reserve(crash_base, crash_size);
>>> +
>>> +	} else {
>>> +		/* User specifies base address explicitly. */
>>> +		if (!memblock_is_region_memory(crash_base, crash_size) ||
>>> +			memblock_is_region_reserved(crash_base, crash_size)) {
>>> +			pr_warn("crashkernel has wrong address or size\n");
>>> +			return;
>>> +		}
>>> +
>>> +		if (crash_base & ((1 << 21) - 1)) {
>>> +			pr_warn("crashkernel base address is not 2MB aligned\n");
>>> +			return;
>>> +		}
>>> +
>>> +		memblock_reserve(crash_base, crash_size);
>>> +	}
>>> +
>>> +	pr_info("Reserving %lldMB of memory at %lldMB for crashkernel\n",
>>> +		crash_size >> 20, crash_base >> 20);
>>> +
>>> +	crashk_res.start = crash_base;
>>> +	crashk_res.end = crash_base + crash_size - 1;
>>> +}
>>> +#else
>>> +static void __init reserve_crashkernel(void)
>>> +{
>>> +	;
>>> +}
>>> +#endif /* CONFIG_KEXEC_CORE */
>>> +
>>>   /*
>>>    * 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
>>
>>
>> Thanks,
>>
>> James
>>

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