From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3F45BC6FD1F for ; Sun, 24 Mar 2024 19:42:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:In-Reply-To:References: Message-ID:Date:Subject:CC:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=jmhlZQWJi9MwV7MfOjqw3rLNPLk+HgMkzZXKcQ1KoFo=; b=OyVL4zfIk/qcR4 nys9I+nf4OYACu2yri0WCL17miyANu7Yi9T5L2STiB1qUocS+hAAuy+o4AR9jT0CneuLSwkzAYzts DlYnm0yNMAc9raAwDqUH/x7LntYX/myUKYGQgRBODZ9mnZsIWKtZ2v5WK8foerAkNP0ETTSowABbF 6lk/nlGFiicV25w4O4wZlSx5ViI8322I9/fmwQDPluZLabUJ95N2O1bzQB90nRIMmiBo3nSYcudlA R/Cgcs7ZnmN+u3834t6+0Sawch7dk/idtaHPmnzjz9ZwIO7FxzlLEfL2V/aEK9h6jSuj6Hc12tVSp pFTPKbE83J56xrIzFyTg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1roTjy-0000000DKD2-193V; Sun, 24 Mar 2024 19:42:46 +0000 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1roTjt-0000000DKC5-3jWj for linux-riscv@lists.infradead.org; Sun, 24 Mar 2024 19:42:44 +0000 Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with both STARTTLS and AUTH (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-167-cBerPzxMMvq7r4HSCZcRYg-1; Sun, 24 Mar 2024 19:42:32 +0000 X-MC-Unique: cBerPzxMMvq7r4HSCZcRYg-1 Received: from AcuMS.Aculab.com (10.202.163.4) by AcuMS.aculab.com (10.202.163.4) with Microsoft SMTP Server (TLS) id 15.0.1497.48; Sun, 24 Mar 2024 19:42:01 +0000 Received: from AcuMS.Aculab.com ([::1]) by AcuMS.aculab.com ([::1]) with mapi id 15.00.1497.048; Sun, 24 Mar 2024 19:42:01 +0000 From: David Laight To: 'Alexandre Ghiti' , Samuel Holland , Alexandre Ghiti CC: Palmer Dabbelt , "linux-riscv@lists.infradead.org" , Albert Ou , "Andrew Morton" , Charlie Jenkins , Guo Ren , Jisheng Zhang , Kemeng Shi , "Matthew Wilcox (Oracle)" , "Mike Rapoport (IBM)" , Paul Walmsley , Xiao Wang , Yangyu Chen , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH] riscv: Define TASK_SIZE_MAX for __access_ok() Thread-Topic: [PATCH] riscv: Define TASK_SIZE_MAX for __access_ok() Thread-Index: AQHaeh3F9DUQSIkEB0u5Xt52XMTyX7FHT0cA Date: Sun, 24 Mar 2024 19:42:01 +0000 Message-ID: References: <20240313180010.295747-1-samuel.holland@sifive.com> <88de4a1a-047e-4be9-b5b0-3e53434dc022@sifive.com> In-Reply-To: Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240324_124242_262661_BB487615 X-CRM114-Status: GOOD ( 10.92 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org ... > The use of alternatives allows to return right away if the buffer is > beyond the usable user address space, and it's not just "slightly > faster" for some cases (a very large buffer with only a few bytes being > beyond the limit or someone could fault-in all the user pages and fail > very late...etc). access_ok() is here to guarantee that such situations > don't happen, so actually it makes more sense to use an alternative to > avoid that. Is it really worth doing ANY optimisations for the -EFAULT path? They really don't happen. The only fault path that matters is the one that has to page in data from somewhere. Provided there is a gap between the highest valid user address and the lowest valid kernel address (may not be true on some 32bit systems) and copy_to/from_user() do 'increasing address' copies then the access_ok() check they do can almost certainly ignore the length. This may be true for pretty much all access_ok() tests? It would certainly simplify the test. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv