From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [103.22.144.67]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3wfJkQ4mlmzDqLt for ; Fri, 2 Jun 2017 19:26:38 +1000 (AEST) 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> 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 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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