[PATCH v6 00/10] kdump: reduce vmcore size and capture time
Baoquan He
baoquan.he at linux.dev
Thu Sep 3 00:31:39 PDT 2026
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?
>
> 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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