Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751305AbdFBMQp (ORCPT ); Fri, 2 Jun 2017 08:16:45 -0400 Received: from gate.crashing.org ([63.228.1.57]:35796 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751125AbdFBMQo (ORCPT ); Fri, 2 Jun 2017 08:16:44 -0400 Message-ID: <1496405473.2842.9.camel@kernel.crashing.org> Subject: Re: [PATCH 2/5] powerpc/mm: split store_updates_sp() in two parts in do_page_fault() From: Benjamin Herrenschmidt To: Christophe LEROY , Michael Ellerman , Paul Mackerras , Scott Wood Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Date: Fri, 02 Jun 2017 22:11:13 +1000 In-Reply-To: <6daf8f4e-9b39-d585-2c64-9b0348fef123@c-s.fr> References: <58f17a04cee5726467ef4e283dfbd7da68fa6ab4.1492606298.git.christophe.leroy@c-s.fr> <871sr23flh.fsf@concordia.ellerman.id.au> <6daf8f4e-9b39-d585-2c64-9b0348fef123@c-s.fr> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.22.6 (3.22.6-2.fc25) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 466 Lines: 13 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. Cheers, Ben.