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Message-ID: <3407c779-9e7e-8f90-353f-c2b58992aae2@huawei.com>
Date: Wed, 28 Jan 2026 17:10:15 +0800
From: Jinjie Ruan <ruanjinjie@...wei.com>
To: Mike Rapoport <rppt@...nel.org>
CC: <ardb@...nel.org>, <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@...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>,
<cfsworks@...il.com>, <osandov@...com>, <sourabhjain@...ux.ibm.com>,
<jbohac@...e.cz>, <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 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@...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(-)
>>
>> 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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