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Message-Id: <a6947d82-d7e3-414c-ac29-1a27257f379f@app.fastmail.com>
Date: Tue, 27 Jan 2026 23:45:53 +0100
From: "Ard Biesheuvel" <ardb@...nel.org>
To: "Jinjie Ruan" <ruanjinjie@...wei.com>, leitao@...ian.org, corbet@....net,
catalin.marinas@....com, will@...nel.org, akpm@...ux-foundation.org,
bp@...en8.de, mingo@...nel.org, pawan.kumar.gupta@...ux.intel.com,
feng.tang@...ux.alibaba.com, "Kees Cook" <kees@...nel.org>, elver@...gle.com,
arnd@...db.de, fvdl@...gle.com, lirongqing@...du.com, bhelgaas@...gle.com,
bhe@...hat.com, dave.hansen@...ux.intel.com, rppt@...nel.org,
cfsworks@...il.com, osandov@...com, sourabhjain@...ux.ibm.com,
jbohac@...e.cz, "Ryan Roberts" <ryan.roberts@....com>,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] arm64: kexec: Add support for crashkernel CMA reservation
On Mon, 26 Jan 2026, at 09:13, 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.
>
> Signed-off-by: Jinjie Ruan <ruanjinjie@...wei.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(-)
>
Thanks for respinning the commit log.
I am not an expert but this looks reasonable to me, so
Acked-by: Ard Biesheuvel <ardb@...nel.org>
> 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
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