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Thu, 15 Oct 2026 20:21:03 -0700 (PDT) Message-ID: <643bbd4c-1041-43b9-9362-17c5330fc06a@gmail.com> Date: Fri, 16 Oct 2026 11:20:45 +0800 Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 0/8] kdump: reduce vmcore size and capture time From: Wandun To: robh@kernel.org, baoquan.he@linux.dev, rppt@kernel.org, m.szyprowski@samsung.com Cc: catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, chenhuacai@kernel.org, kernel@xen0n.name, pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu, 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: <20261016030855.4062882-1-chenwandun1@gmail.com> Content-Language: en-US In-Reply-To: <20261016030855.4062882-1-chenwandun1@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi all, My SMTP server hit a temporary error (4.3.0) partway through sending this series, so some patches did not make it to the list. I will resend the whole series later. Please ignore the current incomplete set. Sorry for the noise. Best regards, Wandun On 10/16/26 11:08, 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. > > 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 [1]. Better solutions > exist but need extra preparation, so they are left out 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. > > Every patch in this series now carries an Acked-by or Reviewed-by tag. > Patches 2 and 3 have changed since v6, but the changes (a build fix and > a riscv hotplug adaptation) do not alter the logic the tags were given > for, so their tags are kept. If any tag should not be carried, please > let me know and I will drop it. > > > v6 --> v7: > 1. Fix a stale MEMBLOCK_NODUMP flag issue [2]. 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://lore.kernel.org/lkml/20260922090252.B01541F000FF@smtp.kernel.org/ > [2] 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 | 15 ++++++ > 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, 100 insertions(+), 94 deletions(-) >