Re: [PATCH v7 0/9] kdump: reduce vmcore size and capture time

[Mike Rapoport <rppt@kernel.org>]

Hi Wandun,

On Tue, Sep 22, 2026 at 04:42:47PM +0800, 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 MEMBLOCK_NODUMP flag in memblock to filter
> reserved memory on DT-based architectures (arm64, riscv, loongarch).
> Reserved regions are marked MEMBLOCK_NODUMP by default so kdump omits
> them; reusable CMA regions are different because their pages are handed
> back to the buddy allocator and may carry crash-relevant data.
> 
> 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 both ACPI and DT systems
> can benefit from it (suggested by Rob, thanks).

Can you elaborate how ACPI systems filter their reserved memory?
With your patches, the memblock flag becomes a part of DT-only
infrastructure, so that claim that both ACPI and DT benefit from it does
not hold, doesn't it?
 
> Since the reserved memory regions are filtered out, the vmcore is
> smaller in size and faster to produce.
> 
> The series is based on linux-next and is organized as follows:
> 
> Patches 1-3: Preparation and bugfixes: switch riscv crash_mem to memblock,
> 	     fold the duplicated per-arch memblock walks into the weak
>              defaults, and serialize crash header preparation against
>              memory hotplug.
> Patches 4-8: NODUMP infrastructure: switch crash_core to
>              for_each_mem_region(), introduce the MEMBLOCK_NODUMP flag,
> 	     add a dumpable flag to struct reserved_mem, and mark
> 	     /reserved-memory and /memreserve/ entries with MEMBLOCK_NODUMP
> 	     flag.
> Patch 9:     Exclude MEMBLOCK_NODUMP regions from the vmcore ELF
>              header.
> 
> v6 --> v7:
> 1. Fix a stale MEMBLOCK_NODUMP flag issue [1]. Memory reserved and
>    marked as NODUMP may later be freed (the initrd, for example),
>    so the NODUMP flag must be cleared accordingly. Since the fix is
>    part of the NODUMP infrastructure introduced by patch 5, it has
>    been folded into that patch.
> 
> 2. Drop the "generic" related description in the cover letter.
> 
> 3. Collect the Acked-by and Reviewed-by tags received during the v6
>    review (thanks to Baoquan, Mike, Rob and Marek). Patch 5 is the
>    only one without a tag, as its Reviewed-by was dropped when the
>    fix was folded in.
> 
> 4. Drop patch 1 of v6, which has been merged separately.
> 
> 
> v5 --> v6:
> 1. Serialize crash header preparation against memory hotplug to avoid
>    out-of-bounds or use-after-free issues.
> 2. MEMBLOCK_NODUMP marking is now done after memblock allows resizing,
>    avoiding a panic from too few regions before resize is permitted.
> 3. Reordered the patches, put pre-existing bugfixes earlier in the series.
> 
> 
> 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].
> 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.
> 
> 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. 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 [3], 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://sashiko.dev/#/message/20260917220750.GA4013814-robh%40kernel.org
> [2] https://lore.kernel.org/lkml/20260723234126.GA3253409-robh@kernel.org/
> [3] https://lore.kernel.org/lkml/20260506144542.GA2072596-robh@kernel.org/
> 
> 
> 
> Wandun Chen (9):
>   riscv: build crash_mem ranges from memblock instead of resource tree
>   crash_core: fold duplicated memblock arch hooks into the weak default
>   crash_core: serialize crash header preparation against hotplug
>   crash_core: replace for_each_mem_range() with for_each_mem_region()
>   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
>   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 --------------
>  arch/x86/kernel/crash.c                    |  2 +-
>  drivers/of/fdt.c                           |  2 +
>  drivers/of/of_private.h                    |  2 +
>  drivers/of/of_reserved_mem.c               | 48 ++++++++++++++++++++
>  include/linux/crash_core.h                 |  2 +
>  include/linux/memblock.h                   |  9 ++++
>  include/linux/of_reserved_mem.h            |  1 +
>  kernel/crash_core.c                        | 51 ++++++++++++++++++++--
>  kernel/dma/contiguous.c                    |  1 +
>  mm/memblock.c                              | 43 +++++++++++++++++-
>  14 files changed, 155 insertions(+), 97 deletions(-)
> 
> -- 
> 2.43.0
> 

-- 
Sincerely yours,
Mike.