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@huawei.com>
---
 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..0ee679167664 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)
+			return ret;
+	}
+
 	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

Hello Jinjie,

On Fri, Jan 23, 2026 at 03:48:20PM +0800, Jinjie Ruan wrote:
> Extend crashkernel CMA reservation support to arm64.

This is awesome. I was waiting for this patch! Thanks for working on it.

> @@ -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)
> +			return ret;

Don't you want to "goto out" here, given you want to free cmem.

earlirer in this function, it does:

	cmem = kmalloc(struct_size(cmem, ranges, nr_ranges), GFP_KERNEL);

you probably want to free it before returning an error, given
prepare_elf_headers() will return an error, which will fail load image,
causing the memory leak for cmem above.

On Fri, 23 Jan 2026 at 10:30, Breno Leitao <leitao@debian.org> wrote:
>
> Hello Jinjie,
>
> On Fri, Jan 23, 2026 at 03:48:20PM +0800, Jinjie Ruan wrote:
> > Extend crashkernel CMA reservation support to arm64.
>
> This is awesome. I was waiting for this patch! Thanks for working on it.
>

That is great!

But the commit log contains no motivation whatsoever why this is such
a good thing, so perhaps one of you can enlighten us? This endless
fiddling with boot-time memory reservations doesn't make the system
more robust, so having a good reason in the commit log why this change
is needed is really needed.