[PATCH v4] powerpc/kdump: Add support for crashkernel CMA reservation

[Ritesh Harjani (IBM)]

Sourabh Jain <sourabhjain at linux.ibm.com> writes:

> 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.
>
> Extend crashkernel CMA reservation support to powerpc.
>
> The following changes are made to enable CMA reservation on powerpc:
>
> - 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 in the usable memory ranges for the
>   kdump kernel to use.
> - Exclude the CMA-reserved ranges from the crash kernel memory to
>   prevent them from being exported through /proc/vmcore.
>
> With the introduction of the CMA crashkernel regions,
> crash_exclude_mem_range() needs to be called multiple times to exclude
> both crashk_res and crashk_cma_ranges from the crash memory ranges. To
> avoid repetitive logic for validating mem_ranges size and handling
> reallocation when required, this functionality is moved to a new wrapper
> function crash_exclude_mem_range_guarded().
>
> To ensure proper CMA reservation, reserve_crashkernel_cma() is called
> after pageblock_order is initialized.
>
> Cc: Baoquan he <bhe at redhat.com>
> Cc: Jiri Bohac <jbohac at suse.cz>
> Cc: Hari Bathini <hbathini at linux.ibm.com>
> Cc: Madhavan Srinivasan <maddy at linux.ibm.com>
> Cc: Mahesh Salgaonkar <mahesh at linux.ibm.com>
> Cc: Michael Ellerman <mpe at ellerman.id.au>
> Cc: Ritesh Harjani (IBM) <ritesh.list at gmail.com>
> Cc: Shivang Upadhyay <shivangu at linux.ibm.com>
> Cc: linuxppc-dev at lists.ozlabs.org
> Signed-off-by: Sourabh Jain <sourabhjain at linux.ibm.com>
> ---
> Changlog:
>
> v3 -> v4
>  - Removed repeated initialization to tmem in
>    crash_exclude_mem_range_guarded()
>  - Call crash_exclude_mem_range() with right crashk ranges
>
> ---
>  arch/powerpc/include/asm/kexec.h   |  2 ++
>  arch/powerpc/kernel/setup-common.c |  4 ++-
>  arch/powerpc/kexec/core.c          | 10 ++++++-
>  arch/powerpc/kexec/ranges.c        | 43 ++++++++++++++++++++++--------
>  4 files changed, 46 insertions(+), 13 deletions(-)


I am not much familiar with the crash kernel workings but was curious
about the following query related to this patch:

As I understand this patch allows for the remaining crash kernel
memory to come from CMA region. But do we limit the CMA region to be lower
than 4G? Is this patch dependent over your other patch series [1] which
supports high crashkernel reservation?

[1]: https://lore.kernel.org/linuxppc-dev/20251027151338.819957-1-sourabhjain@linux.ibm.com/


A minor comment: I guess we could reflect the support for ,cma for PPC
too in Documentation/admin-guide/kernel-parameters.txt like how it is
done for x86.


-ritesh