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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id ECA44C433F5 for ; Wed, 23 Feb 2022 23:35:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244831AbiBWXfc (ORCPT ); Wed, 23 Feb 2022 18:35:32 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55672 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244692AbiBWXf2 (ORCPT ); Wed, 23 Feb 2022 18:35:28 -0500 Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 3C20B59A6A for ; Wed, 23 Feb 2022 15:34:59 -0800 (PST) Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 21NNReM1024539; Wed, 23 Feb 2022 17:27:40 -0600 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 21NNRd3Z024538; Wed, 23 Feb 2022 17:27:39 -0600 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Wed, 23 Feb 2022 17:27:39 -0600 From: Segher Boessenkool To: Gabriel Paubert Cc: Christophe Leroy , Kees Cook , linux-kernel@vger.kernel.org, Paul Mackerras , linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH] powerpc/32: Clear volatile regs on syscall exit Message-ID: <20220223232739.GJ614@gate.crashing.org> References: <28b040bd2357a1879df0ca1b74094323f778a472.1645636285.git.christophe.leroy@csgroup.eu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.3i Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 23, 2022 at 09:48:09PM +0100, Gabriel Paubert wrote: > On Wed, Feb 23, 2022 at 06:11:36PM +0100, Christophe Leroy wrote: > > + /* Zero volatile regs that may contain sensitive kernel data */ > > + li r0,0 > > + li r4,0 > > + li r5,0 > > + li r6,0 > > + li r7,0 > > + li r8,0 > > + li r9,0 > > + li r10,0 > > + li r11,0 > > + li r12,0 > > + mtctr r0 > > + mtxer r0 > > Here, I'm almost sure that on some processors, it would be better to > separate mtctr form mtxer. mtxer is typically very expensive (pipeline > flush) but I don't know what's the best ordering for the average core. mtxer is cheaper than mtctr on many cores :-) On p9 mtxer is cracked into two latency 3 ops (which run in parallel). While mtctr has latency 5. On p8 mtxer was horrible indeed (but nothing near as bad as a pipeline flush). Segher