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 X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AF59EC00306 for ; Thu, 5 Sep 2019 17:01:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8CEA720CC7 for ; Thu, 5 Sep 2019 17:01:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390915AbfIERBl (ORCPT ); Thu, 5 Sep 2019 13:01:41 -0400 Received: from mx2.mailbox.org ([80.241.60.215]:61604 "EHLO mx2.mailbox.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1733299AbfIERBk (ORCPT ); Thu, 5 Sep 2019 13:01:40 -0400 Received: from smtp2.mailbox.org (smtp2.mailbox.org [80.241.60.241]) (using TLSv1.2 with cipher ECDHE-RSA-CHACHA20-POLY1305 (256/256 bits)) (No client certificate requested) by mx2.mailbox.org (Postfix) with ESMTPS id A0FCBA01CE; Thu, 5 Sep 2019 19:01:34 +0200 (CEST) X-Virus-Scanned: amavisd-new at heinlein-support.de Received: from smtp2.mailbox.org ([80.241.60.241]) by spamfilter05.heinlein-hosting.de (spamfilter05.heinlein-hosting.de [80.241.56.123]) (amavisd-new, port 10030) with ESMTP id l96lis2EinZ8; Thu, 5 Sep 2019 19:01:30 +0200 (CEST) Date: Fri, 6 Sep 2019 03:01:06 +1000 From: Aleksa Sarai To: Peter Zijlstra Cc: Al Viro , Jeff Layton , "J. Bruce Fields" , Arnd Bergmann , David Howells , Shuah Khan , Shuah Khan , Ingo Molnar , Christian Brauner , Rasmus Villemoes , Eric Biederman , Andy Lutomirski , Andrew Morton , Alexei Starovoitov , Kees Cook , Jann Horn , Tycho Andersen , David Drysdale , Chanho Min , Oleg Nesterov , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Aleksa Sarai , Linus Torvalds , containers@lists.linux-foundation.org, linux-alpha@vger.kernel.org, linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, linux-xtensa@linux-xtensa.org, sparclinux@vger.kernel.org Subject: Re: [PATCH v12 01/12] lib: introduce copy_struct_{to,from}_user helpers Message-ID: <20190905170106.7j4nmgwnvkcwn6md@yavin.dot.cyphar.com> References: <20190904201933.10736-1-cyphar@cyphar.com> <20190904201933.10736-2-cyphar@cyphar.com> <20190905073205.GY2332@hirez.programming.kicks-ass.net> <20190905092622.tlb6nn3uisssdfbu@yavin.dot.cyphar.com> <20190905094305.GJ2349@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="kmvm5dxbzyhfjvqj" Content-Disposition: inline In-Reply-To: <20190905094305.GJ2349@hirez.programming.kicks-ass.net> Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org --kmvm5dxbzyhfjvqj Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2019-09-05, Peter Zijlstra wrote: > On Thu, Sep 05, 2019 at 07:26:22PM +1000, Aleksa Sarai wrote: > > On 2019-09-05, Peter Zijlstra wrote: > > > On Thu, Sep 05, 2019 at 06:19:22AM +1000, Aleksa Sarai wrote: > > > > + > > > > + while (rest > 0) { > > > > + size_t bufsize =3D min(rest, sizeof(buffer)); > > > > + > > > > + if (__copy_from_user(buffer, addr, bufsize)) > > > > + return -EFAULT; > > > > + if (memchr_inv(buffer, 0, bufsize)) > > > > + return -E2BIG; > > > > + > > > > + addr +=3D bufsize; > > > > + rest -=3D bufsize; > > > > + } > > >=20 > > > The perf implementation uses get_user(); but if that is too slow, sur= ely > > > we can do something with uaccess_try() here? > >=20 > > Is there a non-x86-specific way to do that (unless I'm mistaken only x86 > > has uaccess_try() or the other *_try() wrappers)? The main "performance > > improvement" (if you can even call it that) is that we use memchr_inv() > > which finds non-matching characters more efficiently than just doing a > > loop. >=20 > Oh, you're right, that's x86 only :/ Though, I just had an idea -- am I wrong to think that the following would work just as well (without the need for an intermediate buffer)? if (memchr_inv((const char __force *) src + size, 0, rest)) return -E2BIG; Or is this type of thing very much frowned upon? What if it was a separate memchr_inv_user() instead -- I feel as though there's not a strong argument for needing to use a buffer when we're single-passing the __user buffer and doing a basic boolean check. --=20 Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH --kmvm5dxbzyhfjvqj Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQSxZm6dtfE8gxLLfYqdlLljIbnQEgUCXXE/TgAKCRCdlLljIbnQ Eo4lAP4vz7qxi6aZbZTeed0ZbnEtPkuMnCkFo0v18rHfgnM6xgD/bV/SICkzrufH DwNHgRAu5z8daivqeybakfQqvQMhpA4= =SteT -----END PGP SIGNATURE----- --kmvm5dxbzyhfjvqj--