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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 18037C433EF for ; Thu, 24 Feb 2022 09:10:53 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4K46Zg1RH1z3fxw for ; Thu, 24 Feb 2022 20:10:51 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.crashing.org (client-ip=63.228.1.57; helo=gate.crashing.org; envelope-from=segher@kernel.crashing.org; receiver=) Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) by lists.ozlabs.org (Postfix) with ESMTP id 4K46PK2N2lz3f3T for ; Thu, 24 Feb 2022 20:02:43 +1100 (AEDT) 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 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 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linuxppc-dev@lists.ozlabs.org, Paul Mackerras , Kees Cook , linux-kernel@vger.kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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