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

[Leizhen (ThunderTown)]

On 2022/2/11 18:51, Baoquan He wrote:
> On 02/11/22 at 06:41pm, Leizhen (ThunderTown) wrote:
>>
>>
>> On 2022/2/11 18:30, Baoquan He wrote:
>>> On 01/24/22 at 04:47pm, Zhen Lei wrote:
>>>> From: Chen Zhou <chenzhou10 at huawei.com>
>>> ......
>>>> 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
>>>>   *
>>>> @@ -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;
>>>
>>> Here, the error case is not checked and handled. But it still gets
>>> expeced result which is the default SZ_256M. Is this designed on
>>> purpose?
>>
>> Yes, we can specify only "crashkernel=X,high".
>>
>> This is mentioned in Documentation/admin-guide/kernel-parameters.txt
>>
>>         crashkernel=size[KMG],low
>>                         [KNL, X86-64] range under 4G. When crashkernel=X,high
>>                         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
>>                         requires at least 64M+32K low memory, also enough extra
>>                         low memory is needed to make sure DMA buffers for 32-bit
>>                         devices won't run out. Kernel would try to allocate at     <---------
>>                         least 256M below 4G automatically.                         <---------
> 
> Yeah, that is expected becasue no crahskernel=,low is a right usage. The
> 'ret' is 0 in the case. If I gave below string, it works too.
> "crashkernel=256M,high crashkernel=aaabbadfadfd,low"

Yes, so maybe we should change the error code in __parse_crashkernel()
from "-EINVAL" to "-ENOENT" when the specified option does not exist.

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 256cf6db573cd09..395f4fac1773f28 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -243,9 +243,8 @@ static int __init __parse_crashkernel(char *cmdline,
        *crash_base = 0;

        ck_cmdline = get_last_crashkernel(cmdline, name, suffix);
-
        if (!ck_cmdline)
-               return -EINVAL;
+               return -ENOENT;

        ck_cmdline += strlen(name);


> 
>>
>>>
>>>> +
>>>> +		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