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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 A2584C43387 for ; Fri, 21 Dec 2018 21:07:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6D68821929 for ; Fri, 21 Dec 2018 21:07:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="bOJCF+U1" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388423AbeLUVHb (ORCPT ); Fri, 21 Dec 2018 16:07:31 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:36726 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388154AbeLUVHa (ORCPT ); Fri, 21 Dec 2018 16:07:30 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=OEXYdZpJ5heyKiGxKBrWzRjppUh95Jb5QndoCrwt2F8=; b=bOJCF+U1k/EoJ9awRM6H5P3LM Yp7qS32fCkyR6Xo0DyVeND+KyLmIi7nZTIa9R7bgtuBokRoJ+hYdGAqEJcMUiho5AQheuOF9B8QtM /J/9BHGQKrd+UWVKpWLzD/kXXYUVt8YSLvf82QBr+yN0bUgjx98IrqyKzaQ064/eoEVOkz4B0aoVI YUrvASvjGW+zfeadf9VpUhfv/HhHgW0VgQUbfgHnwIrAW5SRMUlF8Z1N4rjYNK67ZvUl74A7kHjbA YdR7P0HKNICTkQzLO1OdpInYonm/rwDmJtLx23fRBat4+IPguyksMzJ8X8ttJkPu0E1fK/wc1ccO+ j+cw3XA+Q==; Received: from willy by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1gaS0v-0000b0-Ui; Fri, 21 Dec 2018 21:07:21 +0000 Date: Fri, 21 Dec 2018 13:07:21 -0800 From: Matthew Wilcox To: Cyrill Gorcunov Cc: Igor Stoppa , Andy Lutomirski , Peter Zijlstra , Dave Hansen , Mimi Zohar , Thiago Jung Bauermann , igor.stoppa@huawei.com, Nadav Amit , Kees Cook , Ahmed Soliman , linux-integrity@vger.kernel.org, kernel-hardening@lists.openwall.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 01/12] x86_64: memset_user() Message-ID: <20181221210721.GK10600@bombadil.infradead.org> References: <20181221181423.20455-1-igor.stoppa@huawei.com> <20181221181423.20455-2-igor.stoppa@huawei.com> <20181221182515.GF10600@bombadil.infradead.org> <20181221200546.GA8441@uranus> <20181221202946.GJ10600@bombadil.infradead.org> <20181221204616.GC8441@uranus> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181221204616.GC8441@uranus> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org On Fri, Dec 21, 2018 at 11:46:16PM +0300, Cyrill Gorcunov wrote: > Cast to unsigned char is needed in any case. And as far as I remember > we've been using this multiplication trick for a really long time > in x86 land. I'm out of sources right now but it should be somewhere > in assembly libs. x86 isn't the only CPU. Some CPUs have slow multiplies but fast shifts. Also loading 0x0101010101010101 into a register may be inefficient on some CPUs.