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