[PATCH v20 3/5] arm64: kdump: reimplement crashkernel=X

Leizhen (ThunderTown) thunder.leizhen at huawei.com
Wed Feb 16 17:57:57 PST 2022



On 2022/2/16 18:20, Baoquan He wrote:
> On 02/16/22 at 10:58am, Leizhen (ThunderTown) wrote:
>>
>>
>> On 2022/2/14 15:53, Leizhen (ThunderTown) wrote:
>>>
>>>
>>> On 2022/2/14 11:52, Baoquan He wrote:
>>>> On 01/24/22 at 04:47pm, Zhen Lei wrote:
>>>> ......
>>>>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>>>>> index 6c653a2c7cff052..a5d43feac0d7d96 100644
>>>>> --- a/arch/arm64/mm/init.c
>>>>> +++ b/arch/arm64/mm/init.c
>>>>> @@ -71,6 +71,30 @@ phys_addr_t arm64_dma_phys_limit __ro_after_init;
>>>>>  #define CRASH_ADDR_LOW_MAX	arm64_dma_phys_limit
>>>>>  #define CRASH_ADDR_HIGH_MAX	MEMBLOCK_ALLOC_ACCESSIBLE
>>>>>  
>>>>> +static int __init reserve_crashkernel_low(unsigned long long low_size)
>>>>> +{
>>>>> +	unsigned long long low_base;
>>>>> +
>>>>> +	/* passed with crashkernel=0,low ? */
>>>>> +	if (!low_size)
>>>>> +		return 0;
>>>>> +
>>>>> +	low_base = memblock_phys_alloc_range(low_size, CRASH_ALIGN, 0, CRASH_ADDR_LOW_MAX);
>>>>> +	if (!low_base) {
>>>>> +		pr_err("cannot allocate crashkernel low memory (size:0x%llx).\n", low_size);
>>>>> +		return -ENOMEM;
>>>>> +	}
>>>>> +
>>>>> +	pr_info("crashkernel low memory reserved: 0x%llx - 0x%llx (%lld MB)\n",
>>>>> +		low_base, low_base + low_size, low_size >> 20);
>>>>> +
>>>>> +	crashk_low_res.start = low_base;
>>>>> +	crashk_low_res.end   = low_base + low_size - 1;
>>>>> +	insert_resource(&iomem_resource, &crashk_low_res);
>>>>> +
>>>>> +	return 0;
>>>>> +}
>>>>> +
>>>>>  /*
>>>>>   * reserve_crashkernel() - reserves memory for crash kernel
>>>>
>>>> My another concern is the crashkernel=,low handling. In this patch, the
>>>> code related to low memory is obscure. Wondering if we should make them
>>>> explicit with a little redundant but very clear code flows. Saying this
>>>> because the code must be very clear to you and reviewers, it may be
>>>> harder for later code reader or anyone interested to understand.
>>>>
>>>> 1) crashkernel=X,high
>>>> 2) crashkernel=X,high crashkernel=Y,low
>>>> 3) crashkernel=X,high crashkernel=0,low
>>>> 4) crashkernel=X,high crashkernel='messy code',low
>>>> 5) crashkernel=X //fall back to high memory, low memory is required then.
>>>>
>>>> It could be me thinking about it too much. I made changes to your patch
>>>> with a tuning, not sure if it's OK to you. Otherwise, this patchset
>>>
>>> I think it's good.
>>>
>>>> works very well for all above test cases, it's ripe to be merged for
>>>> wider testing.
>>>
>>> I will test it tomorrow. I've prepared a little more use cases than yours.
>>
>> After the following modifications, I have tested it and it works well. Passed
>> all the test cases I prepared.
> 
> That's great.
> 
> You might need to add 'crashkernel=xM, crashkernel=0,low',
> 'crashkernel=xM, crashkernel='messy code',low' to your test cases.

Oh, right, I will add them.

> 
>>
>>>
>>> 1) crashkernel=4G						//high=4G, low=256M
>>> 2) crashkernel=4G crashkernel=512M,high crashkernel=512M,low	//high=4G, low=256M, high and low are ignored
>>> 3) crashkernel=4G crashkernel=512M,high				//high=4G, low=256M, high is ignored
>>> 4) crashkernel=4G crashkernel=512M,low				//high=4G, low=256M, low is ignored
>>> 5) crashkernel=4G at 0xe0000000					//high=0G, low=0M, cannot allocate, failed
>>> 6) crashkernel=512M						//high=0G, low=512M
>>> 7) crashkernel=128M						//high=0G, low=128M
>>> 8) crashkernel=512M at 0xde000000		//512M at 3552M		//high=0G, low=512M
>>> 9) crashkernel=4G,high						//high=4G, low=256M
>>> a) crashkernel=4G,high crashkernel=512M,low			//high=4G, low=512M
>>> b) crashkernel=512M,high crashkernel=128M,low			//high=512M, low=128M
>>> c) crashkernel=512M,low						//high=0G, low=0M, invalid
>>>
>>>
>>>>
>>>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>>>> index a5d43feac0d7..671862c56d7d 100644
>>>> --- a/arch/arm64/mm/init.c
>>>> +++ b/arch/arm64/mm/init.c
>>>> @@ -94,7 +94,8 @@ static int __init reserve_crashkernel_low(unsigned long long low_size)
>>>>  
>>>>  	return 0;
>>>>  }
>>>> -
>>>> +/*Words explaining why it's 256M*/
>>>> +#define DEFAULT_CRASH_KERNEL_LOW_SIZE SZ_256M
>>
>> It's an empirical value.
>>
>> 94fb9334182284e8e7e4bcb9125c25dc33af19d4 x86/crash: Allocate enough low memory when crashkernel=high
>>
>>     When the crash kernel is loaded above 4GiB in memory, the
>>     first kernel allocates only 72MiB of low-memory for the DMA
>>     requirements of the second kernel. On systems with many
>>     devices this is not enough and causes device driver
>>     initialization errors and failed crash dumps. Testing by
>>     SUSE and Redhat has shown that 256MiB is a good default
>>     value for now and the discussion has lead to this value as
>>     well. So set this default value to 256MiB to make sure there
>>     is enough memory available for DMA.
> 
> Then, some words like below can be added. I am not confident it's good
> enought, hope someone else can help to polish it.
> 
> /*
>  * This is an empirical value in x86_64 and taken here directly. Please
>  * refer to code comment in reserve_crashkernel_low() of x86_64 for more
>  * details.
>  */
> #define DEFAULT_CRASH_KERNEL_LOW_SIZE SZ_256M

I think it's good. If no correction is made, I will use it.

"code comment" --> "the code comment"

> 
>>
>>
>>>>  /*
>>>>   * reserve_crashkernel() - reserves memory for crash kernel
>>>>   *
>>>> @@ -105,10 +106,10 @@ static int __init reserve_crashkernel_low(unsigned long long low_size)
>>>>  static void __init reserve_crashkernel(void)
>>>>  {
>>>>  	unsigned long long crash_base, crash_size;
>>>> -	unsigned long long crash_low_size = SZ_256M;
>>>> +	unsigned long long crash_low_size;
>>>>  	unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
>>>>  	int ret;
>>>> -	bool fixed_base;
>>>> +	bool fixed_base, high;
>>
>> high = false;
>>
>>>>  	char *cmdline = boot_command_line;
>>>>  
>>>>  	/* crashkernel=X[@offset] */
>>>> @@ -126,7 +127,10 @@ static void __init reserve_crashkernel(void)
>>>>  		ret = parse_crashkernel_low(cmdline, 0, &low_size, &crash_base);
>>>>  		if (!ret)
>>>>  			crash_low_size = low_size;
>>>> +		else
>>>> +			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>>>>  
>>>> +		high = true;
>>>>  		crash_max = CRASH_ADDR_HIGH_MAX;
>>>>  	}
>>>>  
>>>> @@ -134,7 +138,7 @@ static void __init reserve_crashkernel(void)
>>>>  	crash_size = PAGE_ALIGN(crash_size);
>>>>  
>>>>  	/* User specifies base address explicitly. */
>>>> -	if (crash_base)
>>>> +	if (fixed_base)
>>>>  		crash_max = crash_base + crash_size;
>>>>  
>>>>  retry:
>>>> @@ -156,7 +160,10 @@ static void __init reserve_crashkernel(void)
>>>>  		return;
>>>>  	}
>>>>  
>>>> -	if (crash_base >= SZ_4G && reserve_crashkernel_low(crash_low_size)) {
>>>> +	if (crash_base >= SZ_4G && !high) 
>>>> +		crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>>>> +
>>>> +	if (reserve_crashkernel_low(crash_low_size)) {
>>>>  		memblock_phys_free(crash_base, crash_size);
>>>>  		return;
>>>>  	}
>>
>> -       if (crash_base >= SZ_4G && reserve_crashkernel_low(crash_low_size)) {
>> -               memblock_phys_free(crash_base, crash_size);
>> -               return;
>> +       if (crash_base >= SZ_4G) {
>> +               if (!high)
>> +                       crash_low_size = SZ_256M;
>> +
>> +               if (reserve_crashkernel_low(crash_low_size)) {
>> +                       memblock_phys_free(crash_base, crash_size);
>> +                       return;
>> +               }
>>         }
>>
>> Looks like changing 'high' to 'low' would be more accurate. Whether crashkernel=Y,low is specified.
> 
> What I menat is like below, we even can add code comment to make it more
> clearer.

OK, I got it. I'll add the necessary comments. Thanks.

> 
> static void __init reserve_crashkernel(void)
> {
> 
>         /* crashkernel=X[@offset] */
>         ret = parse_crashkernel(cmdline, memblock_phys_mem_size(),
>                                 &crash_size, &crash_base);
>         if (ret || !crash_size) {
>                 unsigned long long low_size;
> 
>                 /* crashkernel=X,high */
>                 ret = parse_crashkernel_high(cmdline, 0, &crash_size, &crash_base);
>                 if (ret || !crash_size)
>                         return;
> 
>                 /* crashkernel=X,low */
>                 ret = parse_crashkernel_low(cmdline, 0, &low_size, &crash_base);
> 		//case #1, crashkernel=yM,low is specified explicitly in cmdline
>                 if (!ret)
>                         crash_low_size = low_size;
> 		else //case #2, crashkernel=yM,low is not specified explicitly
>                         crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> 
> 		//high means crashkernel,high is specified explicitly
> 		high = true;
>                 crash_max = CRASH_ADDR_HIGH_MAX;
>         }
> 
>         fixed_base = !!crash_base;
>         crash_size = PAGE_ALIGN(crash_size);
> 
>         /* User specifies base address explicitly. */
>         if (crash_base)
>                 crash_max = crash_base + crash_size;
> retry:
>         crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
>                                                crash_base, crash_max);
>         if (!crash_base) {
>                 /*
>                  * Attempt to fully allocate low memory failed, fall back
>                  * to high memory, the minimum required low memory will be
>                  * reserved later.
>                  */
>                 if (!fixed_base && (crash_max == CRASH_ADDR_LOW_MAX)) {
>                         crash_max = CRASH_ADDR_HIGH_MAX;
>                         goto retry;
>                 }
> 
>                 pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
>                         crash_size);
>                 return;
>         }
> 
> 
> 	//case #3: get crashkernel from high memory through fallback, let's set crashkernel,low too.
>         if (crash_base >= SZ_4G && !high)
> 		crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;	
> 
>         if (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);
> 
>         /*
>          * The crashkernel memory will be removed from the kernel linear
>          * 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);
> }
> 
> 
>>
>>
>>>
>>> It feels like {} may need to be added here so that it is in branch "if (crash_base >= SZ_4G)".
>>> The case of "crashkernel=128M" will not fall back to high memory and does not need to reserve
>>> low memory again.
>>>
>>>>
>>>>>   *
>>>>> @@ -81,29 +105,62 @@ phys_addr_t arm64_dma_phys_limit __ro_after_init;
>>>>>  static void __init reserve_crashkernel(void)
>>>>>  {
>>>>>  	unsigned long long crash_base, crash_size;
>>>>> +	unsigned long long crash_low_size = SZ_256M;
>>>>>  	unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
>>>>>  	int ret;
>>>>> +	bool fixed_base;
>>>>> +	char *cmdline = boot_command_line;
>>>>>  
>>>>> -	ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
>>>>> +	/* crashkernel=X[@offset] */
>>>>> +	ret = parse_crashkernel(cmdline, memblock_phys_mem_size(),
>>>>>  				&crash_size, &crash_base);
>>>>> -	/* no crashkernel= or invalid value specified */
>>>>> -	if (ret || !crash_size)
>>>>> -		return;
>>>>> +	if (ret || !crash_size) {
>>>>> +		unsigned long long low_size;
>>>>>  
>>>>> +		/* crashkernel=X,high */
>>>>> +		ret = parse_crashkernel_high(cmdline, 0, &crash_size, &crash_base);
>>>>> +		if (ret || !crash_size)
>>>>> +			return;
>>>>> +
>>>>> +		/* crashkernel=X,low */
>>>>> +		ret = parse_crashkernel_low(cmdline, 0, &low_size, &crash_base);
>>>>> +		if (!ret)
>>>>> +			crash_low_size = low_size;
>>>>> +
>>>>> +		crash_max = CRASH_ADDR_HIGH_MAX;
>>>>> +	}
>>>>> +
>>>>> +	fixed_base = !!crash_base;
>>>>>  	crash_size = PAGE_ALIGN(crash_size);
>>>>>  
>>>>>  	/* User specifies base address explicitly. */
>>>>>  	if (crash_base)
>>>>>  		crash_max = crash_base + crash_size;
>>>>>  
>>>>> +retry:
>>>>>  	crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
>>>>>  					       crash_base, crash_max);
>>>>>  	if (!crash_base) {
>>>>> +		/*
>>>>> +		 * Attempt to fully allocate low memory failed, fall back
>>>>> +		 * to high memory, the minimum required low memory will be
>>>>> +		 * reserved later.
>>>>> +		 */
>>>>> +		if (!fixed_base && (crash_max == CRASH_ADDR_LOW_MAX)) {
>>>>> +			crash_max = CRASH_ADDR_HIGH_MAX;
>>>>> +			goto retry;
>>>>> +		}
>>>>> +
>>>>>  		pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
>>>>>  			crash_size);
>>>>>  		return;
>>>>>  	}
>>>>>  
>>>>> +	if (crash_base >= SZ_4G && 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);
>>>>>  
>>>>> @@ -112,6 +169,9 @@ 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



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