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Tue, 12 Aug 2025 09:57:49 -0700 (PDT) MIME-Version: 1.0 References: <20250812124941.69508-1-bhe@redhat.com> In-Reply-To: <20250812124941.69508-1-bhe@redhat.com> From: Andrey Konovalov Date: Tue, 12 Aug 2025 18:57:37 +0200 X-Gm-Features: Ac12FXxO7VtFtbvMzrNpRmaaDrUzWKgNXXMRGHfAEt4lFzHjRoU7D-oGMR2kngk 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-Queue-Id: 084C5C0008 X-Rspamd-Server: rspam04 X-Rspam-User: X-Stat-Signature: 4fzoquj517emnq6qums7cy7ra1a8p74x X-HE-Tag: 1755017870-269664 X-HE-Meta: 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 syv00FK0 vWlHmQAyoyuXP61vAfJVz6/owkFtLNY5XDkQCeLVKuHQevfQ4w/7nJbj/+Gjpbdm+TDMtZ8MT/Vk78siI+IrYG4dx8mQ2p/y4WqatEM1JPMKG/1LTcDvmmU51AUoMsKu+bFGFqnwHtrBHXY+pGFwCMt04EI960Yzua8bE72CylGe7iFcgU/CV45YyfJiDApPRE/U6Go16e+JI10AGNFQ4bR8X/wtyAJPxKRgPV/RrHIQY09VXEjR9V9HI/YIoD0YII3AQKIoe0Wv5UHIF6EMDhMLrYg6UZkhawgZoMaG4TXCfvPvtvKcnrp/MNrgogj+s9uZjrWxYI4Rw/XJHK1znOyRe/vIETbfUDpPnRfDGS0UQlh1mxvUXLwKFR7FYpFlsvAweWk2PtxnWPv3a4XSsxbfILX2g90IV+nHzqBy5NyOJHND2+r4HFeLRnIPBmHuPPk3F 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 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 fo= r > 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!