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[213.95.11.211]) by mx.google.com with ESMTPS id d11si7915342wrv.44.2019.06.03.00.41.47 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 03 Jun 2019 00:41:48 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of hch@lst.de designates 213.95.11.211 as permitted sender) client-ip=213.95.11.211; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of hch@lst.de designates 213.95.11.211 as permitted sender) smtp.mailfrom=hch@lst.de Received: by newverein.lst.de (Postfix, from userid 2407) id B4E2E67358; Mon, 3 Jun 2019 09:41:21 +0200 (CEST) Date: Mon, 3 Jun 2019 09:41:21 +0200 From: Christoph Hellwig To: Linus Torvalds Cc: Christoph Hellwig , Paul Burton , James Hogan , Yoshinori Sato , Rich Felker , "David S. Miller" , Nicholas Piggin , Khalid Aziz , Andrey Konovalov , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , linux-mips@vger.kernel.org, Linux-sh list , sparclinux@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Linux-MM , the arch/x86 maintainers , Linux List Kernel Mailing Subject: Re: [PATCH 03/16] mm: simplify gup_fast_permitted Message-ID: <20190603074121.GA22920@lst.de> References: <20190601074959.14036-1-hch@lst.de> <20190601074959.14036-4-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) 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: On Sat, Jun 01, 2019 at 09:14:17AM -0700, Linus Torvalds wrote: > On Sat, Jun 1, 2019 at 12:50 AM Christoph Hellwig wrote: > > > > Pass in the already calculated end value instead of recomputing it, and > > leave the end > start check in the callers instead of duplicating them > > in the arch code. > > Good cleanup, except it's wrong. > > > - if (nr_pages <= 0) > > + if (end < start) > > return 0; > > You moved the overflow test to generic code - good. > > You removed the sign and zero test on nr_pages - bad. I only removed a duplicate of it. The full (old) code in get_user_pages_fast() looks like this: if (nr_pages <= 0) return 0; if (unlikely(!access_ok((void __user *)start, len))) return -EFAULT; if (gup_fast_permitted(start, nr_pages)) {