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=-5.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 67A40C43461 for ; Mon, 7 Sep 2020 10:10:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 11D0E207C3 for ; Mon, 7 Sep 2020 10:10:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1599473411; bh=DdyKvDduyIm5+OD9DDXx1sFF7tQydimT+2MR9Bk8azY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=oZPmXDCG7c9sqkoROnO0nXsnjOLHI9ZnWVn1bnDZhz3G25ITX+vvtG0uJ18Y71TVM I9eo/O/tv59z/46kjjFacN0+sBp24bpSCoKkGJxP5u/4c0kX0uKLCS7tCApIBq6rAc /wLr2BzUH/R11BREnr3pqODCV0Tnau/sSm6T1wMw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728485AbgIGKKJ (ORCPT ); Mon, 7 Sep 2020 06:10:09 -0400 Received: from mail.kernel.org ([198.145.29.99]:50180 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728317AbgIGKKJ (ORCPT ); Mon, 7 Sep 2020 06:10:09 -0400 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E7856207C3; Mon, 7 Sep 2020 10:10:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1599473408; bh=DdyKvDduyIm5+OD9DDXx1sFF7tQydimT+2MR9Bk8azY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=wTjARGHH8jiZcyHd46LUsbd3HkMbc5+QZspww7sL89c1XY8KxDrHWUE5ViYX7oj2E OBv5Mub8sM2uw46ba0922NnR6v8cSmKALYTVlgj8OeYRYVEA5XEt3IvsjQWWctgs+O WnsE2DOQr+M+9a6IY2uBULDHSPtTT7hXIP7bNPv0= Date: Mon, 7 Sep 2020 11:10:03 +0100 From: Will Deacon To: Oli Swede Cc: Catalin Marinas , Robin Murphy , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 00/14] arm64: Optimise and update memcpy, user copy and string routines Message-ID: <20200907101003.GA11970@willie-the-truck> References: <20200630194822.1082-1-oli.swede@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Oli, Thanks for this. Just a few high-level comments below. On Wed, Jul 01, 2020 at 09:12:49AM +0100, Oli Swede wrote: > > Version 3 addressed this but I later found some issues with the fixup > > correctness after further testing, and have partially re-written them > > here, and addressed some other behaviours of the copy algorithm. [...] > I am waiting on access to the relevant machine before posting the benchmark > results for this optimized memcpy, but Sam reported the following with the > similar (but now slightly older) cortex-strings version: > * copy_from_user: 13.17% > * copy_to_user: 4.8% > * memcpy: 27.88% > * copy_in_user: Didn't appear in the test results. > This machine will also be used to check the fixups are accurate on a system > with UAO - they appear to be exact on a non-UAO system with PAN that I've > been working on locally. I'm inclined to say that cortex-strings is probably not a good basis for our uaccess routines. The code needs to be adapted in a non-straightforward way so that we lose pretty much all of the benefits we'd usually get from adopted an existing implementation; we can't pull in fixes or improvements without a lot of manual effort, we can't reuse existing testing infrastructure (see below) and we end up being a "second-class" user of the routines because of the discrepancies in implementation. So why don't we use cortex-strings as a basis for the in-kernel routines only, preferably in a form where the code can be used directly and updated with a script (e.g. similar to how we pull in arch/arm64/crypto routines from OpenSSL). We can then roll our own uaccess routines, using a slightly more straight-forward implementation which is more amenable to handling user faults and doesn't do things like over copying. > I should also mention that the correctness of these routines were tested > using a selftest test module akin to lib/test_user_copy.c (whose usercopy > functionality checks these patches do pass) but which is more specific to > the fixup accuracy, in that it compares the return value with the true > number of bytes remaining in the destination buffer at the point of a fault. Can we put this test module into the kernel source tree, please, maybe as part of lkdtm? Given the control flow of these optimised functions, I think we absolutely need targetted testing to make sure we're getting complete coverage. Will