linux-kernel - Re: [PATCH 1/5] arm64: kdump: Provide default size when crashkernel=Y,low is not specified

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Date:   Fri, 17 Jun 2022 15:39:06 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Baoquan He <bhe@...hat.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>,
        Eric Biederman <ebiederm@...ssion.com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        <devicetree@...r.kernel.org>, Dave Young <dyoung@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>, <kexec@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        <linux-arm-kernel@...ts.infradead.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>,
        "John Donnelly" <John.p.donnelly@...cle.com>,
        Dave Kleikamp <dave.kleikamp@...cle.com>
Subject: Re: [PATCH 1/5] arm64: kdump: Provide default size when
 crashkernel=Y,low is not specified



On 2022/6/17 10:40, Baoquan He wrote:
> On 06/13/22 at 04:09pm, Zhen Lei wrote:
>> To be consistent with the implementation of x86 and improve cross-platform
>> user experience. Try to allocate at least 256 MiB low memory automatically
>> when crashkernel=Y,low is not specified.
> 
> This should correspond to the case that crashkernel=,high is explicitly
> specified, while crashkenrel=,low is omitted. It could be better to
> mention these.

Okay, I'll update the description in the next version.

> 
> Otherwise, this looks good to me.
> 
>>
>> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
>> ---
>>  Documentation/admin-guide/kernel-parameters.txt |  8 +-------
>>  arch/arm64/mm/init.c                            | 12 +++++++++++-
>>  2 files changed, 12 insertions(+), 8 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index 8090130b544b070..61b179232b68001 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -843,7 +843,7 @@
>>  			available.
>>  			It will be ignored if crashkernel=X is specified.
>>  	crashkernel=size[KMG],low
>> -			[KNL, X86-64] range under 4G. When crashkernel=X,high
>> +			[KNL, X86-64, ARM64] range under 4G. When crashkernel=X,high
>                         ~~~~ exceeds 80 characters, it should be OK.
> 
>>  			is passed, kernel could allocate physical memory region
>>  			above 4G, that cause second kernel crash on system
>>  			that require some amount of low memory, e.g. swiotlb
>> @@ -857,12 +857,6 @@
>>  			It will be ignored when crashkernel=X,high is not used
>>  			or memory reserved is below 4G.
>>  
>> -			[KNL, ARM64] range in low memory.
>> -			This one lets the user specify a low range in the
>> -			DMA zone for the crash dump kernel.
>> -			It will be ignored when crashkernel=X,high is not used
>> -			or memory reserved is located in the DMA zones.
>> -
>>  	cryptomgr.notests
>>  			[KNL] Disable crypto self-tests
>>  
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index 339ee84e5a61a0b..5390f361208ccf7 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -96,6 +96,14 @@ phys_addr_t __ro_after_init arm64_dma_phys_limit = PHYS_MASK + 1;
>>  #define CRASH_ADDR_LOW_MAX		arm64_dma_phys_limit
>>  #define CRASH_ADDR_HIGH_MAX		(PHYS_MASK + 1)
>>  
>> +/*
>> + * This is an empirical value in x86_64 and taken here directly. Please
>> + * refer to the code comment in reserve_crashkernel_low() of x86_64 for more
>> + * details.
>> + */
>> +#define DEFAULT_CRASH_KERNEL_LOW_SIZE	\
>> +	max(swiotlb_size_or_default() + (8UL << 20), 256UL << 20)
>> +
>>  static int __init reserve_crashkernel_low(unsigned long long low_size)
>>  {
>>  	unsigned long long low_base;
>> @@ -147,7 +155,9 @@ static void __init reserve_crashkernel(void)
>>  		 * is not allowed.
>>  		 */
>>  		ret = parse_crashkernel_low(cmdline, 0, &crash_low_size, &crash_base);
>> -		if (ret && (ret != -ENOENT))
>> +		if (ret == -ENOENT)
>> +			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>> +		else if (ret)
>>  			return;
>>  
>>  		crash_max = CRASH_ADDR_HIGH_MAX;
>> -- 
>> 2.25.1
>>
> 
> .
> 

-- 
Regards,
  Zhen Lei