Re: [PATCH v6 4/5] arm64: kexec: Add support for crashkernel CMA reservation

[Jinjie Ruan <ruanjinjie@huawei.com>]

On 2026/2/25 23:48, Mike Rapoport wrote:
> On Tue, Feb 24, 2026 at 04:53:41PM +0800, Jinjie Ruan wrote:
>> Commit 35c18f2933c5 ("Add a new optional ",cma" suffix to the
>> crashkernel= command line option") and commit ab475510e042 ("kdump:
>> implement reserve_crashkernel_cma") added CMA support for kdump
>> crashkernel reservation.
>>
>> Crash kernel memory reservation wastes production resources if too
>> large, risks kdump failure if too small, and faces allocation difficulties
>> on fragmented systems due to contiguous block constraints. The new
>> CMA-based crashkernel reservation scheme splits the "large fixed
>> reservation" into a "small fixed region + large CMA dynamic region": the
>> CMA memory is available to userspace during normal operation to avoid
>> waste, and is reclaimed for kdump upon crash—saving memory while
>> improving reliability.
>>
>> So extend crashkernel CMA reservation support to arm64. The following
>> changes are made to enable CMA reservation:
>>
>> - Parse and obtain the CMA reservation size along with other crashkernel
>>   parameters.
>> - Call reserve_crashkernel_cma() to allocate the CMA region for kdump.
>> - Include the CMA-reserved ranges for kdump kernel to use.
>> - Exclude the CMA-reserved ranges from the crash kernel memory to
>>   prevent them from being exported through /proc/vmcore, which is already
>>   done in the crash core.
>>
>> Update kernel-parameters.txt to document CMA support for crashkernel on
>> arm64 architecture.
>>
>> Acked-by: Ard Biesheuvel <ardb@kernel.org>
>> Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
>> ---
>> v3:
>> - Add Acked-by.
>> v2:
>> - Free cmem in prepare_elf_headers()
>> - Add the mtivation.
>> ---
>>  Documentation/admin-guide/kernel-parameters.txt | 2 +-
>>  arch/arm64/kernel/machine_kexec_file.c          | 8 +++++++-
>>  arch/arm64/mm/init.c                            | 5 +++--
>>  3 files changed, 11 insertions(+), 4 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index cb850e5290c2..497f63b76898 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -1121,7 +1121,7 @@ Kernel parameters
>>  			It will be ignored when crashkernel=X,high is not used
>>  			or memory reserved is below 4G.
>>  	crashkernel=size[KMG],cma
>> -			[KNL, X86, ppc] Reserve additional crash kernel memory from
>> +			[KNL, X86, ARM64, ppc] Reserve additional crash kernel memory from
>>  			CMA. This reservation is usable by the first system's
>>  			userspace memory and kernel movable allocations (memory
>>  			balloon, zswap). Pages allocated from this memory range
>> diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
>> index c338506a580b..c8862a762eb3 100644
>> --- a/arch/arm64/kernel/machine_kexec_file.c
>> +++ b/arch/arm64/kernel/machine_kexec_file.c
>> @@ -42,7 +42,7 @@ int arch_kimage_file_post_load_cleanup(struct kimage *image)
>>  #ifdef CONFIG_CRASH_DUMP
>>  unsigned int arch_get_system_nr_ranges(void)
>>  {
>> -	unsigned int nr_ranges = 2; /* for exclusion of crashkernel region */
>> +	unsigned int nr_ranges = 2 + crashk_cma_cnt; /* for exclusion of crashkernel region */
>>  	phys_addr_t start, end;
>>  	u64 i;
>>  
>> @@ -64,6 +64,12 @@ int arch_crash_populate_cmem(struct crash_mem *cmem)
>>  		cmem->nr_ranges++;
>>  	}
>>  
>> +	for (i = 0; i < crashk_cma_cnt; i++) {
>> +		cmem->ranges[cmem->nr_ranges].start = crashk_cma_ranges[i].start;
>> +		cmem->ranges[cmem->nr_ranges].end = crashk_cma_ranges[i].end;
>> +		cmem->nr_ranges++;
>> +	}
> 
> Why do we need to add cma ranges here? They are anyway will be excluded in
> crash_exclude_core_ranges().
> 
> The same comment applies to riscv patch.

Indeed, it should not be placed here. In the kexec DT code, these memory
regions need to be included in the "usable-memory-range",which is
equivalent to the x86 crash_setup_memmap_entries() function.

> 
>>  	return 0;
>>  }
>>  #endif
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index 96711b8578fd..144e30fe9a75 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -96,8 +96,8 @@ phys_addr_t __ro_after_init arm64_dma_phys_limit;
>>  
>>  static void __init arch_reserve_crashkernel(void)
>>  {
>> +	unsigned long long crash_base, crash_size, cma_size = 0;
>>  	unsigned long long low_size = 0;
>> -	unsigned long long crash_base, crash_size;
>>  	bool high = false;
>>  	int ret;
>>  
>> @@ -106,11 +106,12 @@ static void __init arch_reserve_crashkernel(void)
>>  
>>  	ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
>>  				&crash_size, &crash_base,
>> -				&low_size, NULL, &high);
>> +				&low_size, &cma_size, &high);
>>  	if (ret)
>>  		return;
>>  
>>  	reserve_crashkernel_generic(crash_size, crash_base, low_size, high);
>> +	reserve_crashkernel_cma(cma_size);
>>  }
>>  
>>  static phys_addr_t __init max_zone_phys(phys_addr_t zone_limit)
>> -- 
>> 2.34.1
>>
>