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([177.21.143.178]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-73e25941fd9sm7925210b3a.53.2025.04.28.03.57.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Apr 2025 03:57:22 -0700 (PDT) From: Guilherme Giacomo Simoes To: akpm@linux-foundation.org Cc: andreyknvl@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, pasha.tatashin@soleen.com, surenb@google.com, trintaeoitogc@gmail.com Subject: Re: [PATCH] mm: alloc_tag: change the KASAN_TAG_WIDTH for HW_TAGS Date: Mon, 28 Apr 2025 07:57:16 -0300 Message-Id: <20250428105716.151167-1-trintaeoitogc@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20250427172551.fbf81f14d4e6563c13007a65@linux-foundation.org> References: <20250427172551.fbf81f14d4e6563c13007a65@linux-foundation.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 2B90E180012 X-Stat-Signature: mbf6ktprhnwi5y6nb78st6qnnbeq7zmn X-Rspam-User: X-HE-Tag: 1745837843-425945 X-HE-Meta: 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 KaysP0/b 8E8iiSu0PCZXiBZ5ykTWlmxXxLTPUY9QA6qMVXFWom4TQ1eWv7w2WA/N4hJfcG2iqLC8vvRYb2wtOhfot3s3kHNLs5qxqFLpHl0E8/FHrkBIqvgeMh20fzQaLcC13cfqV4HiV4RyL3kH3nuCZu7cM7azP7g4+DajrCZdkWnlSsGpzfiYZNuq9epkOYJmQVGTS0jGO3Ugc7sn1qXijdv4K0L2thyFTIGNv1m657ZmF59tBc6hgn7weyy4RkHOUlxb1bc8NcdbHNmu1Cgv8Ap586jpsz+1WHsFiod0mxYaBqcEYSkkj+m02gbnwBNoI2OqXHloisnRbyoc8HnprGURSPn9MqQzA2e7amDq8SWu9bRVLn+DZo3IK7dKT9EQAygCWGPYs5PoaB6bmQjTrBaeDJyutGfMOhgplx+8MCRxm8WyWc/T+X2tIG+xoVuaT+NeqG5eIXIo/Dov/TVM= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000003, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Andrew Morton wrote: > > the KASAN_TAG_WIDTH is 8 bits for both (HW_TAGS and SW_TAGS), but for > > HW_TAGS the KASAN_TAG_WIDTH can be 4 bits bits because due to the design > > of the MTE the memory words for storing metadata only need 4 bits. > > Change the preprocessor define KASAN_TAG_WIDTH for check if SW_TAGS is > > define, so KASAN_TAG_WIDTH should be 8 bits, but if HW_TAGS is define, > > so KASAN_TAG_WIDTH should be 4 bits. > > Why? > > I assume the effect is to save a few flags bits under some > circumstances? But that's just me guessing - please fully describe the > motivation and effects within changelogs. Ok, I will change the commit message with the "why", and send a v2. Thanks.