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=-2.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FROM,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 7E497C43387 for ; Fri, 21 Dec 2018 21:17:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4ADBE2192D for ; Fri, 21 Dec 2018 21:17:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="AGahK594" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391989AbeLUVRo (ORCPT ); Fri, 21 Dec 2018 16:17:44 -0500 Received: from mail-lf1-f66.google.com ([209.85.167.66]:36009 "EHLO mail-lf1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388463AbeLUVRo (ORCPT ); Fri, 21 Dec 2018 16:17:44 -0500 Received: by mail-lf1-f66.google.com with SMTP id a16so4850025lfg.3; Fri, 21 Dec 2018 13:17:43 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=Nw6acrcLU19Xw4fdc5+xJxz54d3g4VoJ0jU4KWrfj3c=; b=AGahK594YjAUkXRnXRBBtoKpmGll80LGkMJ0kZBqIanHTV6LDZb3hfH/K2wQrCo2dH JxsDmdm0ltK9Jv+y4mDSw4tPtOiBTl0nTrcKfQAB6b7C4QiMs0+rz8ymDpZN6ipXKwL6 jbGQpQGfrIYLQPYHjHvOC2vnIIA7ITzu5oLNT2J7j3OhZC/SiZrToeWr4J40DJGYg6Yy 0tU3CPKCLsKNEZg3chO52UIDarV51GgkmJbDMxzcS+cRC+G746vtc7LoVWdaVfQjiHP7 f+PwvQBvQb7kih3n/rvcVtIbWU7UBeEeWxpHJE0iXenXm8xAQDafXiKQYOAsBcvXc4Rp eWfw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=Nw6acrcLU19Xw4fdc5+xJxz54d3g4VoJ0jU4KWrfj3c=; b=cLyE9/NzNk6Q1uLq0otzqMypAKihGpUBgFgdDBwYWyRdLMF0bFXnWU53/tsQ+yfjgQ jXzf3az4Fxe0S9W9pcr3uLTbHkMKHi7h39E5DsVnyuD+OxHTS/FuGYJGuraTkJWU5K7T HrZlNYbhlSbxRd35NjattFNdNWckdNiVDshqs+Wtr+OuR7MhRqh4XC4/3+gwMeJ8xSFX egwxGPUpiLgvjyGIjxT1W5jzgrQq0zXV+I0Yki4uxqzIY5HURibEhh7EE+Qh4KtQFaY9 +fVt/3qzDr8HEfM/imVmUTXPkxZEhW2LUkWz7Cdf30uSQueykMp9dhyugihytWxgoWoN ovLg== X-Gm-Message-State: AA+aEWaGc/MmP43hsL6jT/WJ0pircZIJKXO3olugo6QK+pL/w+I95eID 6FLU9isGIlBetA6uRGfBFu0= X-Google-Smtp-Source: AFSGD/WcJhnykNupqVa5TdIns8nUNKv+NqRWKvwbWzQ+qmGBpRZXhnl5GH/5uBu8VpBAmYjuwziAjQ== X-Received: by 2002:a19:4f0c:: with SMTP id d12mr2227221lfb.121.1545427062174; Fri, 21 Dec 2018 13:17:42 -0800 (PST) Received: from uranus.localdomain ([5.18.103.226]) by smtp.gmail.com with ESMTPSA id s20sm4963537lfb.51.2018.12.21.13.17.40 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 21 Dec 2018 13:17:40 -0800 (PST) Received: by uranus.localdomain (Postfix, from userid 1000) id EE823460769; Sat, 22 Dec 2018 00:17:39 +0300 (MSK) Date: Sat, 22 Dec 2018 00:17:39 +0300 From: Cyrill Gorcunov To: Matthew Wilcox 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: <20181221211739.GD8441@uranus> 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> <20181221210721.GK10600@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181221210721.GK10600@bombadil.infradead.org> User-Agent: Mutt/1.10.1 (2018-07-13) 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 01:07:21PM -0800, Matthew Wilcox wrote: > 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. This is x86-64 patch, not some generic code. > Also loading 0x0101010101010101 into a register may be inefficient on > some CPUs. It is pretty efficient on x86-64. Moreover the self dependents as a |= a << b is a source for data hazards inside cpu engine. Anyway i'm not going to insist, just wanted to remind about such trick. Up to you what to choose.