From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6F19BC2BA19 for ; Wed, 15 Apr 2020 22:08:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3FC5E20784 for ; Wed, 15 Apr 2020 22:08:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725856AbgDOWIT (ORCPT ); Wed, 15 Apr 2020 18:08:19 -0400 Received: from gate.crashing.org ([63.228.1.57]:56671 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725796AbgDOWHf (ORCPT ); Wed, 15 Apr 2020 18:07:35 -0400 Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 03FM6sb4027212; Wed, 15 Apr 2020 17:06:54 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 03FM6rJd027211; Wed, 15 Apr 2020 17:06:53 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Wed, 15 Apr 2020 17:06:52 -0500 From: Segher Boessenkool To: Christophe Leroy Cc: Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , npiggin@gmail.com, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH] powerpc/uaccess: Use flexible addressing with __put_user()/__get_user() Message-ID: <20200415220652.GW26902@gate.crashing.org> References: <4fdc2aba6f5e51887d1cd0fee94be0989eada2cd.1586942312.git.christophe.leroy@c-s.fr> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4fdc2aba6f5e51887d1cd0fee94be0989eada2cd.1586942312.git.christophe.leroy@c-s.fr> User-Agent: Mutt/1.4.2.3i Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi! On Wed, Apr 15, 2020 at 09:20:26AM +0000, Christophe Leroy wrote: > At the time being, __put_user()/__get_user() and friends only use > register indirect with immediate index addressing, with the index > set to 0. Ex: > > lwz reg1, 0(reg2) This is called a "D-form" instruction, or sometimes "offset addressing". Don't talk about an "index", it confuses things, because the *other* kind is called "indexed" already, also in the ISA docs! (X-form, aka indexed addressing, [reg+reg], where D-form does [reg+imm], and both forms can do [reg]). > Give the compiler the opportunity to use other adressing modes > whenever possible, to get more optimised code. Great :-) > --- a/arch/powerpc/include/asm/uaccess.h > +++ b/arch/powerpc/include/asm/uaccess.h > @@ -114,7 +114,7 @@ extern long __put_user_bad(void); > */ > #define __put_user_asm(x, addr, err, op) \ > __asm__ __volatile__( \ > - "1: " op " %1,0(%2) # put_user\n" \ > + "1: " op "%U2%X2 %1,%2 # put_user\n" \ > "2:\n" \ > ".section .fixup,\"ax\"\n" \ > "3: li %0,%3\n" \ > @@ -122,7 +122,7 @@ extern long __put_user_bad(void); > ".previous\n" \ > EX_TABLE(1b, 3b) \ > : "=r" (err) \ > - : "r" (x), "b" (addr), "i" (-EFAULT), "0" (err)) > + : "r" (x), "m" (*addr), "i" (-EFAULT), "0" (err)) %Un on an "m" operand doesn't do much: you need to make it "m<>" if you want pre-modify ("update") insns to be generated. (You then will want to make sure that operand is used in a way GCC can understand; since it is used only once here, that works fine). > @@ -130,8 +130,8 @@ extern long __put_user_bad(void); > #else /* __powerpc64__ */ > #define __put_user_asm2(x, addr, err) \ > __asm__ __volatile__( \ > - "1: stw %1,0(%2)\n" \ > - "2: stw %1+1,4(%2)\n" \ > + "1: stw%U2%X2 %1,%2\n" \ > + "2: stw%U2%X2 %L1,%L2\n" \ > "3:\n" \ > ".section .fixup,\"ax\"\n" \ > "4: li %0,%3\n" \ > @@ -140,7 +140,7 @@ extern long __put_user_bad(void); > EX_TABLE(1b, 4b) \ > EX_TABLE(2b, 4b) \ > : "=r" (err) \ > - : "r" (x), "b" (addr), "i" (-EFAULT), "0" (err)) > + : "r" (x), "m" (*addr), "i" (-EFAULT), "0" (err)) Here, it doesn't work. You don't want two consecutive update insns in any case. Easiest is to just not use "m<>", and then, don't use %Un (which won't do anything, but it is confusing). Same for the reads. Rest looks fine, and update should be good with that fixed as said. Reviewed-by: Segher Boessenkool Segher