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

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Date:   Sat, 7 May 2022 12:30:33 -0500
From:   John Donnelly <John.p.donnelly@...cle.com>
To:     Baoquan He <bhe@...hat.com>, Zhen Lei <thunder.leizhen@...wei.com>,
        Catalin Marinas <catalin.marinas@....com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org, Dave Young <dyoung@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        kexec@...ts.infradead.org, Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        linux-doc@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>,
        Feng Zhou <zhoufeng.zf@...edance.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Chen Zhou <dingguo.cz@...group.com>,
        Dave Kleikamp <dave.kleikamp@...cle.com>,
        John Donnelly <john.p.donnelly@...cle.com>
Subject: Re: [PATCH v24 3/6] arm64: kdump: Reimplement crashkernel=X

On 5/6/22 6:10 PM, 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 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.

Lets get this added and tested with a broader audience. It has been in 
review since March, 4th 2019 - 3+ years. I applaud Zhen for his 
endurance and patience in carrying this for so long.


> 
>> +	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
>>
>