Subject: Re: [PATCH v9 4/5] arm64: kexec: Add support for crashkernel CMA reservation

From: Breno Leitao <[email-masked]>
Date: Mon, 23 Mar 2026 09:42:38 -0700

On Mon, Mar 23, 2026 at 07:17:21PM +0800, Jinjie Ruan wrote:
> 
> 
> On 2026/3/23 18:20, Breno Leitao wrote:
> > On Mon, Mar 23, 2026 at 03:27:44PM +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: Rob Herring (Arm) <[email-masked]>
> >> Acked-by: Baoquan He <[email-masked]>
> >> Acked-by: Mike Rapoport (Microsoft) <[email-masked]>
> >> Acked-by: Ard Biesheuvel <[email-masked]>
> >> Signed-off-by: Jinjie Ruan <[email-masked]>
> >> ---
> >> v7:
> >> - Correct the inclusion of CMA-reserved ranges for kdump
> >>   kernel in of/kexec.
> >> 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          | 2 +-
> >>  arch/arm64/mm/init.c                            | 5 +++--
> >>  drivers/of/fdt.c                                | 9 +++++----
> >>  drivers/of/kexec.c                              | 9 +++++++++
> >>  5 files changed, 19 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> >> index cb850e5290c2..afb3112510f7 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..cc577d77df00 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 */
> > 
> > You update arch_get_system_nr_ranges() to account for CMA ranges, but
> > prepare_elf_headers() in the same file (line 51) still has the
> > hardcoded:
> > 
> >         nr_ranges = 2; /* for exclusion of crashkernel region */
> 
> I don't see any logic related to prepare_elf_headers() or hardcoded
> nr_ranges = 2 in the arm64 implementation.

Just ignore me here, I've mis applied the patch, and then I got
arch_get_system_nr_ranges() and prepare_elf_headers(), but, they are the
same thing at in here.

> > 
> > and does not exclude CMA ranges from cmem. If the generic crash core
> > handles CMA exclusion from vmcore, then shouldn't
> > arch_get_system_nr_ranges() also not need this change?
> >