[PATCH v6 00/10] kdump: reduce vmcore size and capture time
Baoquan He
baoquan.he at linux.dev
Thu Sep 3 02:38:11 PDT 2026
On 09/03/26 at 03:43pm, Wandun wrote:
>
>
> On 9/3/26 15:31, Baoquan He wrote:
> > On 09/03/26 at 03:05pm, Wandun wrote:
> >>
> >>
> >> On 9/2/26 16:53, Baoquan He wrote:
> >>> Hi Wandun,
> >>>
> >>> On 09/02/26 at 03:31pm, Wandun Chen wrote:
> >>>> From: Wandun Chen <chenwandun at 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 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].
> >>>
> >>> Thanks for the effort. I am not against this patchset, and I haven't
> >>> went through it carefully. Just from the cover letter, you mentioned
> >>> generic, I am wondering if this can be generic for excluding other
> >>> memory regions. Asking this because I try to find a way to exclude
> >>> unwanted memory regions too, please check below link where there's
> >>> the relevant discussion. We definitely don't like inventing wheels
> >>> time after time. Do you think this memblock region excluding can
> >>> be used in other places of kernel?
> >>>
> >>> https://lore.kernel.org/all/aoLFai0gzzH2bGgy@MiWiFi-R3L-srv/T/#u
> >>
> >>
> >> Thanks for taking a look, and for the pointer to the crash-wipe thread.
> >>
> >> To answer your question directly: the exclusion mechanism in this series
> >> is already generic, memblock_mark_nodump() is the entry point. Any code
> >> that wants a region out of the vmcore just marks it MEMBLOCK_NODUMP, when
> >> preparing vmcore elf header by walking memblock, these regionss are skipped;
> >> This series is simply one caller, marking the DTS /reserved-memory and
> >> /memreserve/ regions with MEMBLOCK_NODUMP.
> >
> > Thanks, for memory not allocated from memblock, e.g buddy, is it still
> > good?
>
> Yes, still good, only need to pass the physical range to memblock_mark_nodump().
That's interesting. If drivers or any component allocate memory from
buddy, then you will call memblock_mark_nodump() to mark the region
specifically (memblock_setclr_flag will split regions if it's a sub
region of existing memblock region), it won't impact anything?
>
> >
> >>
> >> x86 currently builds the vmcore elf header from iomem_resource, not
> >> memblock; it could be switched to memblock, but that would bring no
> >> benefit for the problem this series solves, so this series makes no
> >> x86 change. I'd personally be in favor of switching to memblock for
> >> a unified implementation across architectures.
> >>
> >> Best regards
> >> Wandun
> >>
> >>
> >>>
> >>>>
> >>>> 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.
> >>>>
> >>>> 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@kernel.org/
> >>>> [2] https://lore.kernel.org/lkml/20260818092420.2859026-1-chenwandun1@gmail.com/
> >>>> [3] https://lore.kernel.org/lkml/20260506144542.GA2072596-robh@kernel.org/
> >>>>
> >>>> 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(-)
> >>>>
> >>>> --
> >>>> 2.43.0
> >>>>
> >>
>
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