Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751785AbdFEKte convert rfc822-to-8bit (ORCPT ); Mon, 5 Jun 2017 06:49:34 -0400 Received: from ozlabs.org ([103.22.144.67]:56331 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751300AbdFEKtd (ORCPT ); Mon, 5 Jun 2017 06:49:33 -0400 From: Michael Ellerman To: Christophe LEROY , Benjamin Herrenschmidt , Paul Mackerras , Scott Wood Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH 2/5] powerpc/mm: split store_updates_sp() in two parts in do_page_fault() In-Reply-To: References: <58f17a04cee5726467ef4e283dfbd7da68fa6ab4.1492606298.git.christophe.leroy@c-s.fr> <871sr23flh.fsf@concordia.ellerman.id.au> <6daf8f4e-9b39-d585-2c64-9b0348fef123@c-s.fr> <1496405473.2842.9.camel@kernel.crashing.org> User-Agent: Notmuch/0.21 (https://notmuchmail.org) Date: Mon, 05 Jun 2017 20:49:30 +1000 Message-ID: <87poeir9ol.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1083 Lines: 26 Christophe LEROY writes: > Le 02/06/2017 à 14:11, Benjamin Herrenschmidt a écrit : >> On Fri, 2017-06-02 at 11:39 +0200, Christophe LEROY wrote: >>> The difference between get_user() and __get_user() is that get_user() >>> performs an access_ok() in addition. >>> >>> Doesn't access_ok() only checks whether addr is below TASK_SIZE to >>> ensure it is a valid user address ? >> >> Do you have a measurable improvement by skipping that check ? I agree >> with your reasoning but I'm also paranoid and so I wouldn't change it >> unless it's really worth it. >> > > No I don't have. Taking into account the patch following this serie > which limits even more the calls to get_user(), it is probably not worth > it anymore (see https://patchwork.ozlabs.org/patch/757564/) > > I will then have to resubmit the entire serie (including that additional > one), but there is no get_user_inatomic() so will have to either: > - do the access_ok() verification inside the function I think open coding the access_ok() check is probably the best option. cheers