Re: [PATCH v6 00/10] kdump: reduce vmcore size and capture time

[Mike Rapoport]

Hi,

On Tue, Sep 15, 2026 at 09:01:07PM +0800, Wandun wrote:
> On 9/2/26 15:31, Wandun Chen wrote:
> > From: Wandun Chen <chenwandun@xxxxxxxxxxx>
> > 
> > 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 default are marked MEMBLOCK_NODUMP 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 the mechanism is generic and
> > both ACPI and DT systems can benefit from it (suggested by Rob, thanks) [1].
> > 
> > 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 1-4: Preparation and bugfixes: fix the missing HugeTLB
> >              flagname, 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 5-9: 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 10:    Exclude MEMBLOCK_NODUMP regions from the vmcore ELF
> >              header.
> 
> Hi,
> 
> Gentle ping on the remaining patches of this series.
> Patches 1, 7, 8 and 9 have been reviewed (thanks Mike and Marek);
> Still looking for review on patches 2-6 and 10.

I'm waiting for reviews from Baoquan and Dave for crash core patches before
applying this series.
 
> Would appreciate a look when you have a moment, happy to rework
> anything based on feedback.
> 
> Best regards,
> Wanun
> 
> > 
> > In v5, Sashiko found some pre-existing issues related to reserved-memory,
> > and has no dependency on this series, so these issues have been addressed
> > in a separate series [2].
> > 
> > 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. 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://lore.kernel.org/lkml/20260723234126.GA3253409-robh@xxxxxxxxxx/
> > [2] https://lore.kernel.org/lkml/20260818092420.2859026-1-chenwandun1@xxxxxxxxx/
> > [3] https://lore.kernel.org/lkml/20260506144542.GA2072596-robh@xxxxxxxxxx/
> > 
> > Meijing Zhao (1):
> >   mm: memblock: add missing HugeTLB flag name
> > 
> > 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                              | 17 ++++++++
> >  14 files changed, 131 insertions(+), 95 deletions(-)
> > 
> 
> 

-- 
Sincerely yours,
Mike.