Re: [PATCH 1/4] x86: kdump: move reserve_crashkernel_low() into kexec_core.c

[Chen Zhou <chenzhou10@huawei.com>]

Hi James,

Thanks for your review.

On 2019/6/6 0:29, James Morse wrote:
> Hello,
> 
> On 07/05/2019 04:50, Chen Zhou wrote:
>> In preparation for supporting reserving crashkernel above 4G
>> in arm64 as x86_64 does, move reserve_crashkernel_low() into
>> kexec/kexec_core.c.
> 
> 
>> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
>> index 905dae8..9ee33b6 100644
>> --- a/arch/x86/kernel/setup.c
>> +++ b/arch/x86/kernel/setup.c
>> @@ -463,59 +460,6 @@ static void __init memblock_x86_reserve_range_setup_data(void)
>>  # define CRASH_ADDR_HIGH_MAX	MAXMEM
>>  #endif
>>  
>> -static int __init reserve_crashkernel_low(void)
>> -{
>> -#ifdef CONFIG_X86_64
> 
> The behaviour of this #ifdef has disappeared, won't 32bit x86 now try and reserve a chunk
> of unnecessary 'low' memory?
> 
> [...]

At present, reserve_crashkernel_low() is called only when reserving crashkernel above 4G, so i deleted
this #ifdef.
If we called reserve_crashkernel_low() at the beginning of reserve_crashkernel(), i need to add it back.

> 
> 
>> @@ -579,9 +523,13 @@ static void __init reserve_crashkernel(void)
>>  		return;
>>  	}
>>  
>> -	if (crash_base >= (1ULL << 32) && reserve_crashkernel_low()) {
>> -		memblock_free(crash_base, crash_size);
>> -		return;
>> +	if (crash_base >= (1ULL << 32)) {
>> +		if (reserve_crashkernel_low()) {
>> +			memblock_free(crash_base, crash_size);
>> +			return;
>> +		}
>> +
>> +		insert_resource(&iomem_resource, &crashk_low_res);
> 
> 
> Previously reserve_crashkernel_low() was #ifdefed to do nothing if !CONFIG_X86_64, I don't
> see how 32bit is skipping this reservation...
> 
> 
>>  	}
>>  
>>  	pr_info("Reserving %ldMB of memory at %ldMB for crashkernel (System RAM: %ldMB)\n",
>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>> index b9b1bc5..096ad63 100644
>> --- a/include/linux/kexec.h
>> +++ b/include/linux/kexec.h
>> @@ -63,6 +63,10 @@
>>  
>>  #define KEXEC_CORE_NOTE_NAME	CRASH_CORE_NOTE_NAME
>>  
>> +#ifndef CRASH_ALIGN
>> +#define CRASH_ALIGN SZ_128M
>> +#endif
> 
> Why 128M? Wouldn't we rather each architecture tells us its minimum alignment?

Yeah, each architecture should tells us its minimum alignment. I added this default size to
fix compiling error on some architecture which didn't define it. I will add x86_64 and arm64
restriction on reserve_crashkernel_low() and delete this define.

> 
> 
>> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
>> index d714044..3492abd 100644
>> --- a/kernel/kexec_core.c
>> +++ b/kernel/kexec_core.c
>> @@ -39,6 +39,8 @@
>>  #include <linux/compiler.h>
>>  #include <linux/hugetlb.h>
>>  #include <linux/frame.h>
>> +#include <linux/memblock.h>
>> +#include <linux/swiotlb.h>
>>  
>>  #include <asm/page.h>
>>  #include <asm/sections.h>
>> @@ -96,6 +98,60 @@ int kexec_crash_loaded(void)
>>  }
>>  EXPORT_SYMBOL_GPL(kexec_crash_loaded);
>>  
>> +int __init reserve_crashkernel_low(void)
>> +{
>> +	unsigned long long base, low_base = 0, low_size = 0;
>> +	unsigned long total_low_mem;
>> +	int ret;
>> +
>> +	total_low_mem = memblock_mem_size(1UL << (32 - PAGE_SHIFT));
>> +
>> +	/* crashkernel=Y,low */
>> +	ret = parse_crashkernel_low(boot_command_line, total_low_mem,
>> +			&low_size, &base);
>> +	if (ret) {
>> +		/*
>> +		 * two parts from lib/swiotlb.c:
>> +		 * -swiotlb size: user-specified with swiotlb= or default.
>> +		 *
>> +		 * -swiotlb overflow buffer: now hardcoded to 32k. We round it
>> +		 * to 8M for other buffers that may need to stay low too. Also
>> +		 * make sure we allocate enough extra low memory so that we
>> +		 * don't run out of DMA buffers for 32-bit devices.
>> +		 */
>> +		low_size = max(swiotlb_size_or_default() + (8UL << 20),
> 
> SZ_8M?
> 
>> +				256UL << 20);
> 
> SZ_256M?
> 

There is compiling warning "warning: comparison of distinct pointer types lacks a cast" if just use
SZ_8M or SZ_256M. We need cast swiotlb_size_or_default() to type int,so i kept the old as in x86_64.

> 
>> +	} else {
>> +		/* passed with crashkernel=0,low ? */
>> +		if (!low_size)
>> +			return 0;
>> +	}
>> +
>> +	low_base = memblock_find_in_range(0, 1ULL << 32, low_size, CRASH_ALIGN);
>> +	if (!low_base) {
>> +		pr_err("Cannot reserve %ldMB crashkernel low memory, please try smaller size.\n",
>> +		       (unsigned long)(low_size >> 20));
>> +		return -ENOMEM;
>> +	}
>> +
>> +	ret = memblock_reserve(low_base, low_size);
>> +	if (ret) {
>> +		pr_err("%s: Error reserving crashkernel low memblock.\n",
>> +				__func__);
>> +		return ret;
>> +	}
>> +
>> +	pr_info("Reserving %ldMB of low memory at %ldMB for crashkernel (System low RAM: %ldMB)\n",
>> +		(unsigned long)(low_size >> 20),
>> +		(unsigned long)(low_base >> 20),
>> +		(unsigned long)(total_low_mem >> 20));
>> +
>> +	crashk_low_res.start = low_base;
>> +	crashk_low_res.end   = low_base + low_size - 1;
>> +
>> +	return 0;
>> +}
> 
> 
> Thanks,
> 
> James
> 
> .
> 

Thanks,
Chen Zhou


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