Message-ID: <7d7a3e70-6a46-b722-ef48-7206a47185dd@huawei.com>
Date:   Wed, 16 Mar 2022 21:11:30 +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>,
        <linux-kernel@...r.kernel.org>, Dave Young <dyoung@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        <kexec@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        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>,
        "John Donnelly" <John.p.donnelly@...cle.com>,
        Dave Kleikamp <dave.kleikamp@...cle.com>
Subject: Re: [PATCH v21 3/5] arm64: kdump: reimplement crashkernel=X



On 2022/3/16 20:11, Baoquan He wrote:
> On 02/27/22 at 11:07am, Zhen Lei wrote:
>> From: Chen Zhou <chenzhou10@...wei.com>
>>
>> There are following issues in arm64 kdump:
>> 1. We use crashkernel=X to reserve crashkernel below 4G, which
>> will fail when there is no enough low memory.
>> 2. If reserving crashkernel above 4G, in this case, crash dump
>> kernel will boot failure because there is no low memory available
>> for allocation.
>>
>> To solve these issues, change the behavior of crashkernel=X and
>> introduce crashkernel=X,[high,low]. crashkernel=X tries low allocation
>> in DMA zone, and fall back to high allocation if it fails.
>> We can also use "crashkernel=X,high" to select a region above DMA zone,
>> which also tries to allocate at least 256M in DMA zone automatically.
>> "crashkernel=Y,low" can be used to allocate specified size low memory.
>>
>> Signed-off-by: Chen Zhou <chenzhou10@...wei.com>
>> Co-developed-by: Zhen Lei <thunder.leizhen@...wei.com>
>> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
>> ---
>>  arch/arm64/kernel/machine_kexec.c      |   9 ++-
>>  arch/arm64/kernel/machine_kexec_file.c |  12 ++-
>>  arch/arm64/mm/init.c                   | 106 +++++++++++++++++++++++--
>>  3 files changed, 115 insertions(+), 12 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
>> index e16b248699d5c3c..19c2d487cb08feb 100644
>> --- a/arch/arm64/kernel/machine_kexec.c
>> +++ b/arch/arm64/kernel/machine_kexec.c
>> @@ -329,8 +329,13 @@ bool crash_is_nosave(unsigned long pfn)
>>  
>>  	/* in reserved memory? */
>>  	addr = __pfn_to_phys(pfn);
>> -	if ((addr < crashk_res.start) || (crashk_res.end < addr))
>> -		return false;
>> +	if ((addr < crashk_res.start) || (crashk_res.end < addr)) {
>> +		if (!crashk_low_res.end)
>> +			return false;
>> +
>> +		if ((addr < crashk_low_res.start) || (crashk_low_res.end < addr))
>> +			return false;
>> +	}
>>  
>>  	if (!kexec_crash_image)
>>  		return true;
>> diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
>> index 59c648d51848886..889951291cc0f9c 100644
>> --- a/arch/arm64/kernel/machine_kexec_file.c
>> +++ b/arch/arm64/kernel/machine_kexec_file.c
>> @@ -65,10 +65,18 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
>>  
>>  	/* Exclude crashkernel region */
>>  	ret = crash_exclude_mem_range(cmem, crashk_res.start, crashk_res.end);
>> +	if (ret)
>> +		goto out;
>> +
>> +	if (crashk_low_res.end) {
>> +		ret = crash_exclude_mem_range(cmem, crashk_low_res.start, crashk_low_res.end);
>> +		if (ret)
>> +			goto out;
>> +	}
>>  
>> -	if (!ret)
>> -		ret =  crash_prepare_elf64_headers(cmem, true, addr, sz);
>> +	ret = crash_prepare_elf64_headers(cmem, true, addr, sz);
>>  
>> +out:
>>  	kfree(cmem);
>>  	return ret;
>>  }
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index 90f276d46b93bc6..30ae6638ff54c47 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -65,6 +65,44 @@ EXPORT_SYMBOL(memstart_addr);
>>  phys_addr_t arm64_dma_phys_limit __ro_after_init;
>>  
>>  #ifdef CONFIG_KEXEC_CORE
>> +/* Current arm64 boot protocol requires 2MB alignment */
>> +#define CRASH_ALIGN			SZ_2M
>> +
>> +#define CRASH_ADDR_LOW_MAX		arm64_dma_phys_limit
>> +#define CRASH_ADDR_HIGH_MAX		memblock.current_limit
>> +
>> +/*
>> + * 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;
>> +
>> +	/* 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%08llx - 0x%08llx (%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
>>   *
>> @@ -75,30 +113,79 @@ 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_max = arm64_dma_phys_limit;
>> +	unsigned long long crash_low_size;
>> +	unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
>>  	int ret;
> 
> Even though reverse xmas tree style is not enforced, this 'int ret;' is
> really annoying to look at. Maybe move it down two lines.
> 
>> +	bool fixed_base, high = false;
>> +	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) {
>> +		/* crashkernel=X,high */
>> +		ret = parse_crashkernel_high(cmdline, 0, &crash_size, &crash_base);
>> +		if (ret || !crash_size)
>> +			return;
>> +
>> +		/* crashkernel=Y,low */
>> +		ret = parse_crashkernel_low(cmdline, 0, &crash_low_size, &crash_base);
>> +		if (ret == -ENOENT)
>> +			/*
>> +			 * crashkernel=Y,low is not specified explicitly, use
>> +			 * default size automatically.
>> +			 */
>> +			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>> +		else if (ret)
>> +			/* crashkernel=Y,low is specified but Y is invalid */
>> +			return;
>> +
>> +		/* Mark crashkernel=X,high is specified */
>> +		high = true;
>> +		crash_max = CRASH_ADDR_HIGH_MAX;
>> +	}
>>  
>> +	fixed_base = !!crash_base;
>>  	crash_size = PAGE_ALIGN(crash_size);
>>  
>>  	/* User specifies base address explicitly. */
> This is over commenting, can't see why it's needed.
>> -	if (crash_base)
>> +	if (fixed_base)
>>  		crash_max = crash_base + crash_size;
> 
> Hi leizhen,
> 
> I made change on reserve_crashkenrel(), inline comment may be slow.
> Please check and consider if they can be taken.

That's great. Thank you very much.

> 
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 30ae6638ff54..f96351da1e3e 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -109,38 +109,43 @@ static int __init reserve_crashkernel_low(unsigned long long low_size)
>   * This function reserves memory area given in "crashkernel=" kernel command
>   * line parameter. The memory reserved is used by dump capture kernel when
>   * primary kernel is crashing.
> + *
> + * NOTE: Reservation of crashkernel,low is special since its existence
> + * is not independent, need rely on the existence of crashkernel,high.
> + * Hence there are different cases for crashkernel,low reservation:
> + * 1) crashkernel=Y,low is specified explicitly, crashkernel,low takes Y;
> + * 2) crashkernel=,low is not given, while crashkernel=,high is specified,
> + *    take the default crashkernel,low value;
> + * 3) crashkernel=X is specified, while fallback to get a memory region
> + *    in high memory, take the default crashkernel,low value;
> + * 4) crashkernel='invalid value',low is specified, failed the whole
> + *    crashkernel reservation and bail out.
>   */
>  static void __init reserve_crashkernel(void)
>  {
>  	unsigned long long crash_base, crash_size;
>  	unsigned long long crash_low_size;
>  	unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
> -	int ret;
>  	bool fixed_base, high = false;
>  	char *cmdline = boot_command_line;
> +	int ret;
>  
>  	/* crashkernel=X[@offset] */
>  	ret = parse_crashkernel(cmdline, memblock_phys_mem_size(),
>  				&crash_size, &crash_base);
>  	if (ret || !crash_size) {
> -		/* crashkernel=X,high */
>  		ret = parse_crashkernel_high(cmdline, 0, &crash_size, &crash_base);
>  		if (ret || !crash_size)
>  			return;
>  
> -		/* crashkernel=Y,low */
>  		ret = parse_crashkernel_low(cmdline, 0, &crash_low_size, &crash_base);
>  		if (ret == -ENOENT)
> -			/*
> -			 * crashkernel=Y,low is not specified explicitly, use
> -			 * default size automatically.
> -			 */
> +			/* case #2 of crashkernel,low reservation */
>  			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>  		else if (ret)
> -			/* crashkernel=Y,low is specified but Y is invalid */
> +			/* case #4 of crashkernel,low reservation */
>  			return;
>  
> -		/* Mark crashkernel=X,high is specified */
>  		high = true;
>  		crash_max = CRASH_ADDR_HIGH_MAX;
>  	}
> @@ -148,7 +153,6 @@ static void __init reserve_crashkernel(void)
>  	fixed_base = !!crash_base;
>  	crash_size = PAGE_ALIGN(crash_size);
>  
> -	/* User specifies base address explicitly. */
>  	if (fixed_base)
>  		crash_max = crash_base + crash_size;
>  
> @@ -172,11 +176,7 @@ static void __init reserve_crashkernel(void)
>  	}
>  
>  	if (crash_base >= SZ_4G) {
> -		/*
> -		 * For case crashkernel=X, low memory is not enough and fall
> -		 * back to reserve specified size of memory above 4G, try to
> -		 * allocate minimum required memory below 4G again.
> -		 */
> +		/* case #3 of crashkernel,low reservation */
>  		if (!high)
>  			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>  
> 
>>  
>> -	/* Current arm64 boot protocol requires 2MB alignment */
>> -	crash_base = memblock_phys_alloc_range(crash_size, SZ_2M,
>> +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) {
>> +		/*
>> +		 * For case crashkernel=X, low memory is not enough and fall
>> +		 * back to reserve specified size of memory above 4G, try to
>> +		 * allocate minimum required memory below 4G again.
>> +		 */
>> +		if (!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);
>>  
>> @@ -107,6 +194,9 @@ 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

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