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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 Subject: Re: [PATCH 0/3] KASAN: HW_TAGS: Disable tagging for stack and page-tables Message-Id: <20260319201057.05d57006408a2f77342eedc2@linux-foundation.org> In-Reply-To: <20260319114952.3241359-1-usama.anjum@arm.com> References: <20260319114952.3241359-1-usama.anjum@arm.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: ykx33tqqzedoucx9ruzh6fgepdmywibu X-Rspamd-Server: rspam09 X-Rspam-User: X-Rspamd-Queue-Id: 535FD20005 X-HE-Tag: 1773976260-81625 X-HE-Meta: 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 F2fNdKBn wbM4zj8gD8ZtEjMabh+54ykDmUvmFj03wJ662cKZyC4pRpm3o/KATfaCGvZNzedr+ELt/72cCBIB0h0CAGb6oxbEnGD0ErEmmwCeX6b5w6MqEK7kndkv4RDYrt5YsJVWEQ3KkgRwlqzVxGTTBfGpF7Bo+LViod4/cHNn0CCXPje+onA+4FcPcOb2299ophhidu7Uii6iknxeqCRrn7jF4WafgpikB4QlQCCqk4dyR01jv8kCR/I45ni2EmGBsjOf/3Gjodpl2BA/50mKX7ccnusrSAj1iRvAgQ+sOCLuCcDT7d3w78CFHw+HEo4u41aH12qSi+gXrKSHMpuLsF3gkUqn0co2F5x52xds5bLb6nImjRFZJVRvEs2P15G84VJQSbO1aVuvWqzccbMa1rzjLBslYAA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 19 Mar 2026 11:49:43 +0000 Muhammad Usama Anjum wrote: > 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. > Some questions from Sashiko: https://sashiko.dev/#/patchset/20260319114952.3241359-1-usama.anjum%40arm.com