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Thu, 12 Nov 2026 00:12:34 -0800 (PST) Received: from [10.125.112.22] ([122.11.210.25]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-8baa7de3eecsm3105447b3a.1.2026.11.12.00.12.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 12 Nov 2026 00:12:33 -0800 (PST) Message-ID: <210ff30c-17a1-4bd1-b943-34a1d0688e43@gmail.com> Date: Thu, 12 Nov 2026 16:12:18 +0800 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 0/8] kdump: reduce vmcore size and capture time To: Mike Rapoport , pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu Cc: robh@kernel.org, baoquan.he@linux.dev, m.szyprowski@samsung.com, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, chenhuacai@kernel.org, kernel@xen0n.name, alex@ghiti.fr, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, saravanak@kernel.org, akpm@linux-foundation.org, pasha.tatashin@soleen.com, pratyush@kernel.org, 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: <20261021083011.2170525-1-chenwandun1@gmail.com> <7773d026-4aef-4169-866a-71ec9a91da21@gmail.com> Content-Language: en-US From: Wandun In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/10/26 16:47, Mike Rapoport wrote: > Hi Wandun, > > On Mon, Nov 09, 2026 at 08:23:16PM +0800, Wandun wrote: >> >> On 10/21/26 16:30, 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. >>> >>> ACPI systems already filter reserved memory out of the vmcore through >>> their existing path: firmware reports those carveouts as unusable in >>> the EFI memory map, they get MEMBLOCK_NOMAP set in memblock.memory >>> (is_usable_memory(), efi-init.c), and the ELF header builder has >>> always skipped nomap regions; only DT-based systems currently fail >>> to filter these regions, which is what this series addresses. >>> >>> This series introduces a MEMBLOCK_NODUMP flag (suggested by Rob) in >>> memblock to filter reserved memory on DT-based architectures. A new >>> flag is needed because MEMBLOCK_NOMAP can only express regions without >>> a linear mapping, while MEMBLOCK_NODUMP can filter regions that are >>> linearly mapped. Reserved regions are marked MEMBLOCK_NODUMP by default >>> 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. >>> >>> 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 1-3: Preparation and bugfixes: 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 4-7: 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 entries with MEMBLOCK_NODUMP. >>> Patch 8: Skip MEMBLOCK_NODUMP regions when building the vmcore >>> ELF header. >> >> Hi all, >> >> A gentle ping on this series. >> >> I'd appreciate any further feedback, particularly on the >> MEMBLOCK_NODUMP discussion and the issues raised in the Sashiko >> review. > > I'm fine with MEMBLOCK_NODUMP. > The issue Sashiko raised about bound check against cmem->max_nr_ranges > seems valid. Hi Mike, Thanks a lot for the review. Some analysis and plan about "bound check against cmem->max_nr_ranges": After patch 3, the remaining race is x86-specific. The weak defaults are safe: every runtime modification of memblock.memory, hot-add and hot-remove alike, happens under device_hotplug_lock, so with the lock held the count and populate passes walk a stable snapshot. x86 instead walks iomem_resource, and Xen balloon inserts its new System RAM resource before taking device_hotplug_lock() (reserve_additional_memory), which is the one remaining hole. The issue is also pre-existing: before patch 3 there was no locking at all, every hotplug path could race the two passes. The proper fix is to switch x86 over to the memblock-based weak defaults, as patch 2 already did for arm64/loongarch/riscv. Would you prefer to have it in this series, or as a separate follow-up? Both work fine for me. > > I didn't check the reserved mem one. The two Sashiko findings on the reserved-mem (patch 7) will also be addressed in next version. > >> Please let me know if there are any other concerns or suggestions >> before I prepare the next revision. > > I believe that should be rebased to account for reserved memory changes. Sure, the next verison will be rebased on latest linux-next. > The riscv change from resources to memblock needs an Ack from riscv > maintainers. Hi Paul, Palmer, Albert, Patch 1 builds the crash_mem ranges for the vmcore ELF header from memblock instead of the resource tree, so the later MEMBLOCK_NODUMP patches can filter reserved memory from the vmcore on the memblock side. With this, the vmcore size reduction the series brings also applies to riscv. Could you take a look when you have a chance? Best regards, Wandun > > And with all that I can take the next version via kexec tree. > >> Thanks, >> Wandun >> >>> >>> v8 --> v9: >>> 1. Patch 7: Avoid a potential boot panic on SH when NODUMP marking requires >>> memblock resizing before it is allowed, found by Sashiko in [1]. SH supports >>> neither CONFIG_KEXEC_FILE nor CONFIG_CRASH_HOTPLUG, so skip marking when >>> both are disabled. >>> >>> v6 --> v8 (v7 mainly tried to fix the initrd issue on release in v6, >>> that approach is superseded here): >>> 1. Stop marking /memreserve/ regions with NODUMP. v6 marked >>> /memreserve/ regions with NODUMP. But a bootloader may specify >>> a /memreserve/ entry for memory that the kernel later frees >>> (e.g. the initrd), and those pages would then be wrongly >>> filtered out of the vmcore after being reused as normal memory. >>> The v7 fix (clearing the flag in free_reserved_area()) caused >>> a lockless runtime mutation of memblock.memory [2]. Better solutions >>> exist but need extra preparation, so temporarily dropped the patch >>> that introduced the problem to keep this series simple in v8. >>> 2. Fix a build failure in patch 2 with both ARCH_KEEP_MEMBLOCK and >>> MEMORY_HOTPLUG are unset. There the memblock arrays live in >>> .init.data, and the weak defaults referencing them create section >>> mismatches, which turn into build errors when SECTION_MISMATCH_WARN_ONLY >>> is also unset. >>> 3. RISCV recently gained crash hotplug support, so adapt its handler >>> like x86 in patch 3: use __crash_prepare_headers() instead of >>> crash_prepare_headers() to avoid self-deadlock. >>> 4. Update the cover letter per review feedback: describe how ACPI >>> systems filter reserved memory and why a new flag is needed >>> instead of reusing NOMAP. >>> >>> v6 --> v7: >>> 1. Fix a stale MEMBLOCK_NODUMP flag issue [3]. Memory reserved and >>> marked as NODUMP may later be freed (the initrd, for example), >>> so the NODUMP flag must be cleared accordingly. Since the fix is >>> part of the NODUMP infrastructure introduced by patch 5, it has >>> been folded into that patch. >>> 2. Drop the "generic" related description in the cover letter. >>> 3. Collect the Acked-by and Reviewed-by tags received during the v6 >>> review (thanks to Baoquan, Mike, Rob and Marek). Patch 5 is the >>> only one without a tag, as its Reviewed-by was dropped when the >>> fix was folded in. >>> 4. Drop patch 1 of v6, which has been merged separately. >>> >>> >>> 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. >>> >>> [1] https://sashiko.dev/#/patchset/20261016061549.4181390-1-chenwandun1@gmail.com?part=7 >>> [2] https://lore.kernel.org/lkml/20260922090252.B01541F000FF@smtp.kernel.org/ >>> [3] https://sashiko.dev/#/message/20260917220750.GA4013814-robh%40kernel.org >>> >>> v5: https://lore.kernel.org/lkml/20260806093519.2907771-1-chenwandun1@gmail.com/ >>> v4: https://lore.kernel.org/lkml/20260630074715.4126796-1-chenwandun1@gmail.com/ >>> >>> Wandun Chen (8): >>> 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 >>> 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/crash.c | 2 +- >>> arch/riscv/kernel/machine_kexec_file.c | 33 -------------- >>> arch/x86/kernel/crash.c | 2 +- >>> drivers/of/fdt.c | 1 + >>> drivers/of/of_private.h | 1 + >>> drivers/of/of_reserved_mem.c | 18 ++++++++ >>> include/linux/crash_core.h | 2 + >>> include/linux/memblock.h | 9 ++++ >>> include/linux/of_reserved_mem.h | 1 + >>> kernel/crash_core.c | 53 +++++++++++++++++++++- >>> kernel/dma/contiguous.c | 1 + >>> mm/memblock.c | 16 +++++++ >>> 15 files changed, 103 insertions(+), 94 deletions(-) >>> >> >