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Fri, 04 Sep 2026 04:09:11 -0700 (PDT) Message-ID: Date: Fri, 4 Sep 2026 19:08:57 +0800 Precedence: bulk X-Mailing-List: loongarch@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 00/10] kdump: reduce vmcore size and capture time To: Baoquan He Cc: catalin.marinas@arm.com, will@kernel.org, chenhuacai@kernel.org, pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, robh@kernel.org, saravanak@kernel.org, akpm@linux-foundation.org, rppt@kernel.org, pasha.tatashin@soleen.com, pratyush@kernel.org, m.szyprowski@samsung.com, mark.rutland@arm.com, kernel@xen0n.name, alex@ghiti.fr, hpa@zytor.com, ruirui.yang@linux.dev, robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, linux-riscv@lists.infradead.org, devicetree@vger.kernel.org, kexec@lists.infradead.org, linux-mm@kvack.org, iommu@lists.linux.dev References: <20260902073116.802752-1-chenwandun1@gmail.com> <6aef2f48-1cc5-408d-a5a2-2b4b4d45ad7b@gmail.com> From: Chen Wandun In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/3/26 5:38 PM, Baoquan He wrote: > 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 >>>>>> >>>>>> 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? IIUC, it won't impact anyting; memblock_mark_nodump() only set the MEMBLOCK_NODUMP bit on the matching memblock.memory regions, and from the buddy allocator's view, there is nothing changed. The only effect is the region split you already pointed out: marking a sub-range costs up to two extra entries in the memblock.memory region array. Best regards, Wandun > >> >>> >>>> >>>> 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 >>>>>> >>>> >>