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Tue, 12 Aug 2025 10:15:03 -0700 (PDT) MIME-Version: 1.0 References: <20250812124941.69508-1-bhe@redhat.com> In-Reply-To: From: Andrey Konovalov Date: Tue, 12 Aug 2025 19:14:52 +0200 X-Gm-Features: Ac12FXxbfIp4CjdMiDbk99JZKDZitEGnh3AeOJx4PqX8F5dQQ1jZuZRm61N9EdU Message-ID: Subject: Re: [PATCH v2 00/12] mm/kasan: make kasan=on|off work for all three modes To: Baoquan He 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 1274AC0008 X-Stat-Signature: 1zgtcyiye7q3a1xjugcfama536ukeiki X-Rspam-User: X-HE-Tag: 1755018904-934814 X-HE-Meta: U2FsdGVkX192ta7NV2yEr8/7ihQ73MxkmD4Mm9jt+kurviuTBN29GFVgjKT6o8TK9hlfV0K7XPKR0KF31RkNm6p5hMXnMXRvwt2pkDaVyym9YobYtCokm335okvAdBZAisKZjcK7uKhlpiwcxTFm1FJx6Tv+OqlTvjOUEOgSEwpNkQnyp+sumXqta4jXFp6H8GNEAZAAKJYTuwx3+NFixHI0bFhO/qFIFz5NHRXvTiThDUXSt660sxaAC+mWtJvJQHuSv05QvxPgVRUe7ras5/JtCl9ZVSawOjbyJBeV2B4nFCy2EsieNp4HL8C3B5DPlANIH4BR5j5gQArc4zTePU7e5KLadBoj/utXm3JCTysLB/L/VQDU/Ef4kD4n1GUqLXol6B83A1S3TC6ZrPfgOF27O1dVYPOKsCnxsD+7yAqbBvCSZeHPbLR5XHti8PUfByhpZ2VCBL/Ve1Xg6ayk2GS+kbkupxiVqgZEwwcOvnCKaYDIaLAhSrhxtBhaitH+hXeTxCh02QMa+FfWTZeWVsx8P4qX1flRi6OgL3p8AvmlrMXTHdLQ0yrzTFriH0/AqaD87QPN6DRrx5DHV751m0B/356pq4JcngSUau5t6aIbDbyowLsEofYPt9rqSqVPIF6Cucssu9Qpm3mgAXzmuPmx6o7VrmdC9UCF0iC1tcaj8TGFztKebHUN47LCbWy4ACVTpp+Oco2faIoXWEzBjE/0UBnapBssZDmsGufsZUdqcuggRpB6WAvqTXyPVfG3luSADkJ0jkjSfl0Pz160YDsWxuD8gp49A2MOPUxtdj8wnzH/KpPxw0XD+jDd9Hsm3x1mst9P5puULTnmEkXVzmhj/8Hd+OsIozzp3vT/iEa5kYMcL4EGNjgrfY3bG9xOWCARAWvUGa1R6ZlXyj4GXUWMP2G/S3e/pp+LxEe8m1iB0QDnGefm1t5xAAfzbu5AvPw0mf7qOHzptUdHMiU db6k4LPR 8aErtw74SEX9CZ3UFQYpA+KFYd1HagTBiDQaAXHy1b4CLxjPCyb8L9GoHudSAIyDRcZO+tKV/aBZOqvSEBlOB07b4nkiSakqzEAmojDvrBUt6kzTMLsCjtXzG4SD4Zj3/WEMfpDrFq12D1/2jyeD0OiWylpmIu9qL9NTvHNQOMAxfn/TL+4d19Q0B+gYif+H3JZeyO0CCneJGrPmXVy6pvvgHgvo5l8lY8wlbYpXKWrV+GpAEkgDr9epfhNt/OsANnuD4Y2eTV7L+RwdnW4NuZtkXPSY7sMwMEQD08Z/2T8fTRSWchxAxLz0683ARJFyicDYGaaUzB7ooZFHnGHdNM60MHdTn+8xooFYYNRbkeaDexb6246xo37Co+uitrYP9+vcMlwTfCC3VKLPWhFKN2Aus4MEaxUhLeiManRaoDp6hGrfeLivSNQur9Parx+oOdrOK/D2+1fPf6dsYu+u3Q5A5I2XLDknxeAyA 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 Tue, Aug 12, 2025 at 6:57=E2=80=AFPM Andrey Konovalov wrote: > > On Tue, Aug 12, 2025 at 2:49=E2=80=AFPM Baoquan He wrote= : > > > > Currently only hw_tags mode of kasan can be enabled or disabled with > > kernel parameter kasan=3Don|off for built kernel. For kasan generic and > > sw_tags mode, there's no way to disable them once kernel is built. > > This is not convenient sometime, e.g in system kdump is configured. > > When the 1st kernel has KASAN enabled and crash triggered to switch to > > kdump kernel, the generic or sw_tags mode will cost much extra memory > > for kasan shadow while in fact it's meaningless to have kasan in kdump > > kernel. > > > > So this patchset moves the kasan=3Don|off out of hw_tags scope and into > > common code to make it visible in generic and sw_tags mode too. Then we > > can add kasan=3Doff in kdump kernel to reduce the unneeded meomry cost = for > > kasan. > > Hi Baoquan, > > Could you clarify what are you trying to achieve by disabling > Generic/SW_TAGS KASAN via command-line? Do you want not to see any > KASAN reports produced? Or gain back the performance? > > Because for the no reports goal, it would be much easier to add a > command-line parameter to silent the reports. > > And the performance goal can only be partially achieved, as you cannot > remove the compiler instrumentation without rebuilding the kernel. > (What are the boot times for KASAN_GENERIC=3Dn vs KASAN_GENERIC=3Dy + > kasan=3Doff vs KASAN_GENERIC=3Dy btw?) > > Thank you! Ah, you don't want the shadow memory for kdump, sorry, I somehow missed tha= t. I'm not familiar with the internals of kdump, but would it be possible/reasonable to teach kdump to ignore the KASAN shadow region?