Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751168AbdFBJ0l (ORCPT ); Fri, 2 Jun 2017 05:26:41 -0400 Received: from ozlabs.org ([103.22.144.67]:57133 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751128AbdFBJ0k (ORCPT ); Fri, 2 Jun 2017 05:26:40 -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: <58f17a04cee5726467ef4e283dfbd7da68fa6ab4.1492606298.git.christophe.leroy@c-s.fr> References: <58f17a04cee5726467ef4e283dfbd7da68fa6ab4.1492606298.git.christophe.leroy@c-s.fr> User-Agent: Notmuch/0.21 (https://notmuchmail.org) Date: Fri, 02 Jun 2017 19:26:34 +1000 Message-ID: <871sr23flh.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 631 Lines: 18 Christophe Leroy writes: > Only the get_user() in store_updates_sp() has to be done outside > the mm semaphore. All the comparison can be done within the semaphore, > so only when really needed. > > As we got a DSI exception, the address pointed by regs->nip is > obviously valid, otherwise we would have had a instruction exception. > So __get_user() can be used instead of get_user() I don't think that part is true. You took a DSI so there *was* an instruction at NIP, but since then it may have been unmapped by another thread. So I don't think you can assume the get_user() will succeed. cheers