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Wed, 9 Apr 2025 08:51:38 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id lGNiNxo19mfGZQAAD6G6ig (envelope-from ); Wed, 09 Apr 2025 08:51:38 +0000 Message-ID: <42cb9ae4-e479-4f52-8e4c-f4bc3cb54971@suse.cz> Date: Wed, 9 Apr 2025 10:51:43 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: slub - extended kmalloc redzone and dma alignment To: Catalin Marinas , Petr Tesarik Cc: Feng Tang , Harry Yoo , Peng Fan , Hyeonggon Yoo <42.hyeyoo@gmail.com>, David Rientjes , Christoph Lameter , "linux-mm@kvack.org" References: <20250404131239.2a987e58@mordecai> <20250404155303.2e0cdd27@mordecai> <39657cf9-e24d-4b85-9773-45fe26dd16ae@suse.cz> <20250408072732.32db7809@mordecai> From: Vlastimil Babka Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 73E88C0015 X-Stat-Signature: j55c7pgt766rsrbey9d1su4mrom1mzbg X-Rspam-User: X-HE-Tag: 1744188700-865827 X-HE-Meta: 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 tX9b6PKW cz+07HSc3c+n7nQ4uw9Iu+H1HOAeZLZNr023gfco1mT3HaULDUVQ7+Y7K6nTSl+RLjXc94rE0LFFhjjmroQ0FFLfUk+3pqXyLgHQZRUsriBcLGB32d/FU0jS41cn/ixBT7o+h20EwpmH0jX9c0AcVlnpfcODL1UgZR2BsyesegdWlP75ZcIVjKOcKTryOniTbfc0DwM8Tyjx5zM5W+Y0fjNhBLOUHyBfxap9oUJJPAy7GVXLweR3IYlqD+gf4zH7dBYEwbdT3R/p3/GT9mq/eHpjC1VAZ/SqZbQ/F1OYZt3RuV1/j9UhTJ2YqndKV+4SY/15iblhH4drHZX+amlRoPBKI1NrCw3TSifLaG4HhJf3d2ZdINbyWzqvOw6ELF60sDpA8N3uFImt3yYQ= 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 4/8/25 5:07 PM, Catalin Marinas wrote: > Assuming I got kmalloc redzoning right, I think there's still a > potential issue. Let's say we have a system with 128-byte DMA alignment > required (the largest cache line size). We do a kmalloc(104) and > kmalloc_size_roundup() returns 128, so all seems good to the DMA code. > However, kmalloc() redzones from 104 to 128 as it tracks the original > size. The DMA bouncing doesn't spot it since the > kmalloc_size_roundup(104) is aligned to 128. Note that kmalloc_size_roundup() is supposed to be used *before* kmalloc(), such as dma_resv_list_alloc() does. Then there's no issue as no redzoning would not be done between 104 and 128, there would be only the additional redzone at 128+.