Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751270AbdFBMcL (ORCPT ); Fri, 2 Jun 2017 08:32:11 -0400 Received: from pegase1.c-s.fr ([93.17.236.30]:6026 "EHLO pegase1.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751128AbdFBMcK (ORCPT ); Fri, 2 Jun 2017 08:32:10 -0400 Subject: Re: [PATCH 2/5] powerpc/mm: split store_updates_sp() in two parts in do_page_fault() To: Benjamin Herrenschmidt , Michael Ellerman , Paul Mackerras , Scott Wood Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org 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> From: Christophe LEROY Message-ID: Date: Fri, 2 Jun 2017 14:31:47 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1 MIME-Version: 1.0 In-Reply-To: <1496405473.2842.9.camel@kernel.crashing.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1070 Lines: 28 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 - get back to v2 (https://patchwork.ozlabs.org/patch/756234/) - implement an get_user_inatomic() function What would be the best ? Christophe