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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Uladzislau Rezki , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrey Konovalov , Marco Elver , Vincenzo Frascino , Peter Collingbourne , Catalin Marinas , Will Deacon , Ryan.Roberts@arm.com, david.hildenbrand@arm.com Cc: Muhammad Usama Anjum Subject: [PATCH v2 0/3] KASAN: HW_TAGS: Disable tagging for stack and page-tables Date: Tue, 24 Mar 2026 13:26:26 +0000 Message-ID: <20260324132631.482520-1-usama.anjum@arm.com> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: 94hbcnk99mu8bi8ita9wsf3ijwhyrw74 X-Rspamd-Queue-Id: 4117740010 X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1774358810-269888 X-HE-Meta: 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 ERUlwXAI r1OTERaGoPQ3ITvV1B+qDshKdB8ekAvXiQcxYQvhOHR6YteuQgOz53/JXaOp6rF+ZdpuS8xCBNkKUBB8xb0g3t3QvLA4JjfsMP0dFX0yihGKf9TVB2dx2g7/YgpvUzuZrvmZq7e2gOq4/17fvRAtOwmD/zfKvH4igNNzp/EtIq6iuZxzz87aTwGAG7H2iXLGvMJoKbIECQywTz46VkrdI4rYDBWtB3qTUUXwwnAWLYCzniRr5UIiWitA1rndHw+D7Sxh0EAc6rZOM3cA= 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) --- Changes since v1: (summary only) - 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/thread_info.h | 2 +- kernel/fork.c | 5 +++-- mm/vmalloc.c | 11 ++++++++--- 4 files changed, 13 insertions(+), 7 deletions(-) -- 2.47.3