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

[Baoquan He <baoquan.he@linux.dev>]

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@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
> >>>>
> >>
>