Re: [PATCH v24 3/6] arm64: kdump: Reimplement crashkernel=X

[Leizhen (ThunderTown)]

On 2022/5/7 10:07, Baoquan He wrote:
> On 05/07/22 at 09:34am, Leizhen (ThunderTown) wrote:
>>
>>
>> On 2022/5/7 7:10, Baoquan He wrote:
>>> On 05/06/22 at 07:43pm, Zhen Lei wrote:
>>> ......  
>>>> @@ -118,8 +162,7 @@ static void __init reserve_crashkernel(void)
>>>>  	if (crash_base)
>>>>  		crash_max = crash_base + crash_size;
>>>>  
>>>> -	/* Current arm64 boot protocol requires 2MB alignment */
>>>> -	crash_base = memblock_phys_alloc_range(crash_size, SZ_2M,
>>>> +	crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
>>>>  					       crash_base, crash_max);
>>>>  	if (!crash_base) {
>>>>  		pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
>>>> @@ -127,6 +170,11 @@ static void __init reserve_crashkernel(void)
>>>>  		return;
>>>>  	}
>>>>  
>>>
>>> There's corner case missed, e.g
>>> 1) ,high and ,low are specified, CONFIG_ZONE_DMA|DMA32 is not enabled;
>>> 2) ,high and ,low are specified, the whole system memory is under 4G.
>>>
>>> Below judgement can filter them away:
>>>         
>>> 	if (crash_base > arm64_dma_phys_limit && crash_low_size &&
>>> 	    reserve_crashkernel_low(crash_low_size)) {
>>>
>>> What's your opinion? Leave it and add document to notice user, or fix it
>>> with code change?
>>
>> I think maybe we can leave it unchanged. If the user configures two memory ranges,
>> we'd better apply for two. Otherwise, he'll be confused when he inquires. Currently,
>> crash_low_size is non-zero only when 'crashkernel=Y,low' is explicitly configured.
> 
> Then user need know the system information, e.g how much is the high
> memory, low memory, if CONFIG_ZONE_DMA|DMA32 is enabled. And we need
> describe these cases in document. Any corner case or exception need
> be noted if we don't handle it in code.
> 
> Caring about this very much because we have CI with existed test cases
> to run on the system, and QA will check these manually too. Support
> engineer need detailed document if anything special but happened.
> Anything unclear or uncovered will be reported as bug to our kernel dev.
> Guess your company do the similar thing like this.
> 
> This crashkerne,high and crashkernel,low reservation is special if we
> allow ,high, ,low existing in the same zone. Imagine on system with
> CONFIG_ZONE_DMA|DMA32 disabled, people copy the crashkernel=512M,high
> and crashkernel=128M,low from other system, and he could get
> crash_res at [5G, 5G+512M], while crash_low_res at [6G, 6G+128M]. Guess
> how they will judge us.

OK, I got it.

> 
>>
>>>
>>> I would suggest merging this series, Lei can add this corner case
>>> handling on top. Since this is a newly added support, we don't have
>>> to make it one step. Doing step by step can make reviewing easier.
>>>
>>>> +	if (crash_low_size && reserve_crashkernel_low(crash_low_size)) {
>>>> +		memblock_phys_free(crash_base, crash_size);
>>>> +		return;
>>>> +	}
>>>> +
>>>>  	pr_info("crashkernel reserved: 0x%016llx - 0x%016llx (%lld MB)\n",
>>>>  		crash_base, crash_base + crash_size, crash_size >> 20);
>>>>  
>>>> @@ -135,6 +183,9 @@ static void __init reserve_crashkernel(void)
>>>>  	 * map. Inform kmemleak so that it won't try to access it.
>>>>  	 */
>>>>  	kmemleak_ignore_phys(crash_base);
>>>> +	if (crashk_low_res.end)
>>>> +		kmemleak_ignore_phys(crashk_low_res.start);
>>>> +
>>>>  	crashk_res.start = crash_base;
>>>>  	crashk_res.end = crash_base + crash_size - 1;
>>>>  	insert_resource(&iomem_resource, &crashk_res);
>>>> -- 
>>>> 2.25.1
>>>>
>>>
>>> .
>>>
>>
>> -- 
>> Regards,
>>   Zhen Lei
>>
> 
> .
> 

-- 
Regards,
  Zhen Lei