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Sun, 17 Aug 2025 03:40:53 +0000 (UTC) Received: from localhost (unknown [10.72.112.34]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E5A23180044F; Sun, 17 Aug 2025 03:40:50 +0000 (UTC) Date: Sun, 17 Aug 2025 11:40:46 +0800 From: Baoquan He To: Andrey Konovalov Cc: linux-mm@kvack.org, ryabinin.a.a@gmail.com, glider@google.com, dvyukov@google.com, vincenzo.frascino@arm.com, akpm@linux-foundation.org, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, sj@kernel.org, lorenzo.stoakes@oracle.com, elver@google.com, snovitoll@gmail.com Subject: Re: [PATCH v2 00/12] mm/kasan: make kasan=on|off work for all three modes Message-ID: References: <20250812124941.69508-1-bhe@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: C78DA1C0002 X-Stat-Signature: 581ssr49rrhbmi5j3hs7iojr8hbq7q8n X-HE-Tag: 1755402059-286853 X-HE-Meta: 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 F0khTVIx 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 08/16/25 at 06:50am, Andrey Konovalov wrote: > On Thu, Aug 14, 2025 at 10:56 AM Baoquan He wrote: > > > > Ah, I got what you mean. We probably are saying different things. > > > > In order to record memory content of a corrupted kernel, we need reserve > > a memory region during bootup of a normal kernel (usually called 1st > > kernel) via kernel parameter crashkernel=nMB in advance. Then load > > kernel into the crashkernel memory region, that means the region is not > > usable for 1st kernel. When 1st kernel collapsed, we stop the 1st kernel > > cpu/irq and warmly switch to the loaded kernel in the crashkernel memory > > region (usually called kdump kernel). In kdump kernel, it boots up and > > enable necessary features to read out the 1st kernel's memory content, > > we usually use user space tool like makeudmpfile to filter out unwanted > > memory content. > > > > So this patchset intends to disable KASAN to decrease the crashkernel > > meomry value because crashkernel is not usable for 1st kernel. As for > > shadow memory of 1st kernel, we need recognize it and filter it away > > in makedumpfile. > > Ah, I see, thank you for the explanation! > > So kdump kernel runs with the amount of RAM specified by crashkernel=. > And KASAN's shadow memory increases RAM usage, which means > crashkernel= needs to be set to a higher value for KASAN kernels. Is > my understanding of the problem correct? Yeah, you are quite right. When I tested it, on x86_64 and arm64, usually I set crashkernel=256M and it's sufficient. However, when KASAN is enabled and generic mode is taken, I need set crashkernel=768M to make vmcore dumping succeed. In kdump kernel, read_vmcore() uses ioremap to map the old memory of collapsed kernel for reading out, those vmalloc-ed areas are lazily freed and cause more shadow memory than what we usually think shadow memory only costs 1/8 of physical RAM.