Re: [PATCH v5 0/8] kdump: reduce vmcore size and capture time

[Marek Szyprowski <m.szyprowski@samsung.com>]

On 06.08.2026 11:35, Wandun Chen wrote:
> From: Wandun Chen <chenwandun@lixiang.com>
>
> On SoCs that carve out large firmware-owned reserved memory (GPU,
> camera ISP, ...), kdump currently dumps those carveouts as part of
> system RAM even though their contents are firmware state that is not
> useful for kernel crash analysis.
>
> This series introduces a 'dumpable' flag on struct reserved_mem and a
> MEMBLOCK_NODUMP flag in memblock to filter vmcore ELF header on DT-based
> architectures (arm64, riscv, loongarch). Reserved regions default to
> non-dumpable and are marked MEMBLOCK_NODUMP so kdump omits them;
> reusable CMA regions are explicitly marked dumpable in rmem_cma_setup()
> because their pages are handed back to the buddy allocator and may carry
> crash-relevant data.
>
> Since the reserved memory regions are filtered out, the vmcore is
> smaller in size and faster to produce. ACPI systems already filter
> reserved memory out of the vmcore through their existing path; only
> DT-based systems currently fail to filter these regions, which is what
> this series addresses. The flag lives in memblock itself rather than
> in a DT-only structure, so the mechanism is generic and both ACPI and
> DT systems can benefit from it (suggested by Rob, thanks).
>
> The series is based on linux-next and is organized as follows:
>   Patches 1-2: Introduce MEMBLOCK_NODUMP in memblock and the dumpable
>                flag on struct reserved_mem.
>   Patches 3-4: Mark non-dumpable /reserved-memory and /memreserve/
>                entries with MEMBLOCK_NODUMP.
>   Patch 5:     Switch riscv to memblock so the NODUMP flag is visible
>                to the vmcore ELF header builder; add (KEXEC_FILE &&
>                CRASH_DUMP) to riscv's ARCH_KEEP_MEMBLOCK condition.
>   Patches 6-8: Fold the duplicated per-arch memblock walks into the
>                weak defaults in crash_core, switch to
>                for_each_mem_region(), and exclude MEMBLOCK_NODUMP
>                regions from the vmcore ELF header.
>
> v4 --> v5:
> 1. Rework the mechanism around a memblock-level MEMBLOCK_NODUMP flag
>    (suggested by Rob) instead of the v4 opt-in 'dumpable' flag on
>    DT-only struct reserved_mem.
>
> 2. Switch the riscv vmcore elf header preparation to use memblock
>    instead of the resource tree, aligning it with arm64 and loongarch,
>    so riscv also can exclude reserved memory from vmcore.
>
> 3. Deduplicate the vmcore elf header preparation: arm64, riscv and
>    loongarch open-coded the same logic, so fold it into shared
>     __weak defaults in crash_core.
>
> 4.  Drop the v4 patch that saved /memreserve/ entries into the
>     reserved_mem array; /memreserve/ is now marked MEMBLOCK_NODUMP
>     directly.

v5 looks much better, at least from the reserved memory regions perspective.


> v3 --> v4:
> 1. Rebase this series on v7.2-rc1.
> 2. Add two cleanup patches (patch 02/03).
> 3. Simplify patch 03 to avoid checking whether initial_boot_params is
>    NULL multiple times, suggested by Rob.
>
> v2 --> v3:
> 1. Fix out-of-bounds issue if device tree lacks /reserved-memory node.[2]
> 2. Fix UAF issue when alloc_reserved_mem_array() fails.
> 3. Add some prepare patches.
>
> v1 --> v2:
> 1. v1 added an opt-out DT property ('linux,no-dump'). Per Rob's
>    feedback [1], v2 drop that property and exclude reserve memory
>    by default.
> 2. Split some prepared patches from the original patches.
> 3. Address coding-style comments on patch 5 from Rob.
>
> [1] https://lore.kernel.org/lkml/20260506144542.GA2072596-robh@kernel.org/
> [2] https://protect2.fireeye.com/v1/url?k=05b72ed7-643c3bed-05b6a598-74fe4860008a-295907342918bd15&q=1&e=c408484d-fdd8-4fe4-8eee-690e883afb73&u=https%3A%2F%2Fsashiko.dev%2F%23%2Fpatchset%2F20260520091844.592753-1-chenwandun%2540lixiang.com%3Fpart%3D4
>
> Wandun Chen (8):
>   memblock: introduce MEMBLOCK_NODUMP flag
>   of: reserved_mem: add dumpable flag to opt-in vmcore
>   of: reserved_mem: mark /reserved-memory entries with MEMBLOCK_NODUMP
>   of: reserved_mem: mark /memreserve/ entries as MEMBLOCK_NODUMP
>   riscv: build crash_mem ranges from memblock instead of resource tree
>   crash_core: fold duplicated memblock arch hooks into the weak default
>   crash_core: replace for_each_mem_range() with for_each_mem_region()
>   crash_core: skip MEMBLOCK_NODUMP regions when building vmcore ELF
>     header
>
>  arch/arm64/kernel/machine_kexec_file.c     | 29 ------------------
>  arch/loongarch/kernel/machine_kexec_file.c | 27 -----------------
>  arch/riscv/Kconfig                         |  2 +-
>  arch/riscv/kernel/machine_kexec_file.c     | 33 --------------------
>  drivers/of/fdt.c                           |  2 ++
>  drivers/of/of_private.h                    |  1 +
>  drivers/of/of_reserved_mem.c               | 35 ++++++++++++++++++++++
>  include/linux/memblock.h                   |  9 ++++++
>  include/linux/of_reserved_mem.h            |  1 +
>  kernel/crash_core.c                        | 34 +++++++++++++++++++--
>  kernel/dma/contiguous.c                    |  1 +
>  mm/memblock.c                              | 16 ++++++++++
>  12 files changed, 98 insertions(+), 92 deletions(-)
>
Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland