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

From: Mike Rapoport <[email-masked]>
Date: Wed, 25 Feb 2026 17:48:41 +0200

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 <[email-masked]>
> Signed-off-by: Jinjie Ruan <[email-masked]>
> ---
> 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.

>  	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
> 

-- 
Sincerely yours,
Mike.