Re: [PATCH v2] arm64: kexec: Add support for crashkernel CMA reservation

[Jinjie Ruan <ruanjinjie@huawei.com>]

On 2026/1/28 16:31, Mike Rapoport wrote:
> On Mon, Jan 26, 2026 at 04:13:34PM +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.
>>
>> Update kernel-parameters.txt to document CMA support for crashkernel on
>> arm64 architecture.
> 
> I'm looking at this and at almost identical patch for riscv 
> https://lore.kernel.org/all/20260126080738.696723-1-ruanjinjie@huawei.com
> and it feels wrong that we have duplicate the code that excludes cma
> ranges.
> CMA ranges are known to the crash_core and I don't see why we cannot
> exclude them there.

Youa are right, x86 and powerpc has similar implementations that
excludes crashkernel cma ranges.

x86 [1]

+	for (i = 0; i < crashk_cma_cnt; ++i) {
+		ret = crash_exclude_mem_range(cmem, crashk_cma_ranges[i].start,
+					      crashk_cma_ranges[i].end);
+		if (ret)
+			return ret;
+	}
+
+	return 0;

But powerpc [2] is a little different which uses a wrapper for
crash_exclude_mem_range() and more check and realloc_mem_ranges().

+	for (i = 0; i < crashk_cma_cnt; ++i) {
+		ret = crash_exclude_mem_range_guarded(mem_ranges,
crashk_cma_ranges[i].start,
+					      crashk_cma_ranges[i].end);
+		if (ret)
+			goto out;
+	}

[1]: https://lore.kernel.org/all/ZWEAWMJtesa3O9M5@dwarf.suse.cz/
[2]:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b4a96ab50f368afc2360ff539a20254ca2c9a889

>  
>> Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
>> ---
>> v2:
>> - Free cmem in prepare_elf_headers()
>> - Add the mtivation.
>> ---
>>  Documentation/admin-guide/kernel-parameters.txt |  2 +-
>>  arch/arm64/kernel/machine_kexec_file.c          | 15 ++++++++++++++-
>>  arch/arm64/mm/init.c                            |  5 +++--
>>  3 files changed, 18 insertions(+), 4 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index 1058f2a6d6a8..36bb642a7edd 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -1119,7 +1119,7 @@ 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 410060ebd86d..ef6ce9aaba80 100644
>> --- a/arch/arm64/kernel/machine_kexec_file.c
>> +++ b/arch/arm64/kernel/machine_kexec_file.c
>> @@ -48,7 +48,7 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
>>  	u64 i;
>>  	phys_addr_t start, end;
>>  
>> -	nr_ranges = 2; /* for exclusion of crashkernel region */
>> +	nr_ranges = 2 + crashk_cma_cnt; /* for exclusion of crashkernel region */
>>  	for_each_mem_range(i, &start, &end)
>>  		nr_ranges++;
>>  
>> @@ -64,6 +64,12 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
>>  		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++;
>> +	}
>> +
>>  	/* Exclude crashkernel region */
>>  	ret = crash_exclude_mem_range(cmem, crashk_res.start, crashk_res.end);
>>  	if (ret)
>> @@ -75,6 +81,13 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
>>  			goto out;
>>  	}
>>  
>> +	for (i = 0; i < crashk_cma_cnt; ++i) {
>> +		ret = crash_exclude_mem_range(cmem, crashk_cma_ranges[i].start,
>> +					      crashk_cma_ranges[i].end);
>> +		if (ret)
>> +			goto out;
>> +	}
>> +
>>  	ret = crash_prepare_elf64_headers(cmem, true, addr, sz);
>>  
>>  out:
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index 524d34a0e921..28165d94af08 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
>>
>