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h=From:To:Cc:Subject:Date:From; b=lV3ZV6RwQkLW3J5x4BqgxmN8ttA6LqRu1seHzAluQ2D86GgFtc5GbI7b9XjDWdz73 xkqIUOdvTaSvS973Qpn1PvkS9DSsx8Lbq/E5SIWej91BFGVmRLCOAYh5YR/5PeqSR7 z0Vnnh3LgeU5eIZHqFccKERW0haH/xk62312oiHo= From: Dev Jain To: akpm@linux-foundation.org, david@kernel.org, urezki@gmail.com, kees@kernel.org, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, arnd@arndb.de Cc: Dev Jain , ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, tglx@kernel.org, usama.anjum@arm.com, mathieu.desnoyers@efficios.com, linux-arch@vger.kernel.org, ryan.roberts@arm.com, catalin.marinas@arm.com Subject: [PATCH v4 0/3] kasan: hw_tags: Disable tagging for stack and page-tables Date: Wed, 29 Apr 2026 15:57:01 +0530 Message-Id: <20260429102704.680174-1-dev.jain@arm.com> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 2B5454000D X-Stat-Signature: w3r6kfz3xzgc9f6uzsqcknh9p73ot4ac X-Rspam-User: X-HE-Tag: 1777458476-648102 X-HE-Meta: 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 kYsT+CCE CcS7224oX9sq1wYTDq44gW1mHWL9sia+SUp4bc7E64xZdro4lBftISPR07CnEAYD1WdShNBwx8Lkqv7EYfvAvLfTFFEtg47SrmA9j3J+vzhhRGfnf7ToHEIJMO7fFiDsAI6vOT61zMoa/CSslvJ37uf2JcASyC11S9NbDaAhM6ovulSKPx5PjT2HyZ2z4/Nx4rs9DM3BUUKVPtfKBnCevKPZ+/faPCbqtn1HY6K5gOfnZL92Pxtr7UUHTpIWUakx4eEdw4PVLIRN9SCxPzf7pRNW99c9Ylu7eHgoz1kKU6K2DjtlwojhY1XAIAkm5a5WwSX6zmyEHUo1O5zvou2PghpGeC02bZwSTwf6+NMpkswH93ZtLMQ/y6GDh1/cIbQzpWqK2EYm3YoPa5riRy2X3KHWAukAXLYL6gdVFae7AbJV5R0c= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Stacks and page tables are always accessed with the match-all tag, so assigning a new random tag every time at allocation and setting invalid tag at deallocation time, just adds overhead without improving the detection. With __GFP_SKIP_KASAN the page keeps its poison tag and KASAN_TAG_KERNEL (match-all tag) is stored in the page flags while keeping the poison tag in the hardware. The benefit of it is that 256 tag setting instruction per 4 kB page aren't needed at allocation and deallocation time. Thus match-all pointers still work, while non-match tags (other than poison tag) still fault. __GFP_SKIP_KASAN only skips for KASAN_HW_TAGS mode, so coverage is unchanged. Benchmark: The benchmark has two modes. In thread mode, the child process forks and creates N threads. In pgtable mode, the parent maps and faults a specified memory size and then forks repeatedly with children exiting immediately. Thread benchmark: 2000 iterations, 2000 threads: 2.575 s → 2.229 s (~13.4% faster) The pgtable samples: - 2048 MB, 2000 iters 19.08 s → 17.62 s (~7.6% faster) --- Applies on 7-0-rc1. Changes since v3->v4: - Sashiko noticed: https://sashiko.dev/#/patchset/20260424130157.3163009-1-dev.jain%40arm.com Fix this by honouring vmalloc skip via GFP_SKIP_KASAN only in HW tags case, to avoid unintended skipping in SW/generic KASAN. - Instead of removing and adding GFP_SKIP_KASAN into gfp_flags, simply call __get_vm_area_node() without it - Update GFP_SKIP_KASAN documentation - Put missing SOB by me v2->v3: - Directly skip kasan_unpoison_vmalloc() for GFP_SKIP_KASAN in patch 1 v1->v2: - Update description/title - Patch 1: Simplify skip conditions based on the fact that __GFP_SKIP_KASAN - Patch 2: Specify _GFP_SKIP_KASAN in THREADINFO_GFP and GFP_VMAP_STACK Muhammad Usama Anjum (3): vmalloc: add __GFP_SKIP_KASAN support kasan: skip HW tagging for all kernel thread stacks mm: skip KASAN tagging for page-allocated page tables include/asm-generic/pgalloc.h | 2 +- include/linux/gfp_types.h | 6 +++--- include/linux/thread_info.h | 2 +- kernel/fork.c | 5 +++-- mm/vmalloc.c | 13 +++++++++---- 5 files changed, 17 insertions(+), 11 deletions(-) -- 2.34.1