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h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=iwYrN/Qa6hTknYBmnxoeiYRnZy9dpjnSXd21EX835N/H5e0y5K/5tBmuKYrP7CVVG WRSRyAflKnhkB/7TrVh01xquXXc2wsymfnyILjqOS7OOMO0r2kJBjOdf8a4sub5mAj rRNqtoP3/0dDcAw4OGvVjhr40/g9l2/SIeeSmO/s= Date: Thu, 4 Apr 2024 13:15:49 -0700 From: Andrew Morton To: Frank van der Linden Cc: linux-mm@kvack.org, muchun.song@linux.dev, linux-kernel@vger.kernel.org, Marek Szyprowski , David Hildenbrand Subject: Re: [PATCH 1/2] mm/cma: drop incorrect alignment check in cma_init_reserved_mem Message-Id: <20240404131549.27a454072f7e96530dce2d62@linux-foundation.org> In-Reply-To: <20240404162515.527802-1-fvdl@google.com> References: <20240404162515.527802-1-fvdl@google.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=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 49F5B1C000A X-Stat-Signature: f6ntqzrqpazx8e7my43ygm48rdnuaub3 X-Rspam-User: X-HE-Tag: 1712261752-61865 X-HE-Meta: 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 sT8xWf+V XDjKfbDKwec9mZ65EC0mkXqW7bW5yrHfVNZs27VV4mJeCMY/4RQaA9P490wND94wPqsZhNdKERrOg7voPUjF+qCXhg2yardeS/oWMyUj2OsAAG16oFVhT1WDZPSTasaH18U1z7qtsF4AU2bLwe6UZMOJZWHImOPQqU0O59vapE6h5JxOjyMDxYW/PeybMmnNHNjWnvk0eySjfsz1fUXiDyvhFQtTpZDAyL9r8pBhseXO6hn8swNMVkVyMHd24C3nUMxjtzqI8quIdpMKrQudQ4X2JshdSW9rG5ofPmr1bz43gxEg= 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 Thu, 4 Apr 2024 16:25:14 +0000 Frank van der Linden wrote: > cma_init_reserved_mem uses IS_ALIGNED to check if the size > represented by one bit in the cma allocation bitmask is > aligned with CMA_MIN_ALIGNMENT_BYTES (pageblock size). > > However, this is too strict, as this will fail if > order_per_bit > pageblock_order, which is a valid configuration. > > We could check IS_ALIGNED both ways, but since both numbers are > powers of two, no check is needed at all. What are the userspace visible effects of this bug?