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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 C5545C433E0 for ; Wed, 20 Jan 2021 05:44:39 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id EFD232313A for ; Wed, 20 Jan 2021 05:44:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EFD232313A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=codefail.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4DLDxJ5vC6zDr1D for ; Wed, 20 Jan 2021 16:44:36 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=codefail.de (client-ip=131.153.2.45; helo=h4.fbrelay.privateemail.com; envelope-from=cmr@codefail.de; receiver=) Received: from h4.fbrelay.privateemail.com (h4.fbrelay.privateemail.com [131.153.2.45]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4DLDvQ6DwdzDqVr for ; Wed, 20 Jan 2021 16:42:58 +1100 (AEDT) Received: from MTA-08-4.privateemail.com (mta-08.privateemail.com [68.65.122.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by h3.fbrelay.privateemail.com (Postfix) with ESMTPS id B36E1805FC for ; Wed, 20 Jan 2021 00:42:54 -0500 (EST) Received: from MTA-08.privateemail.com (localhost [127.0.0.1]) by MTA-08.privateemail.com (Postfix) with ESMTP id 330D960099; Wed, 20 Jan 2021 00:42:50 -0500 (EST) Received: from localhost (unknown [10.20.151.213]) by MTA-08.privateemail.com (Postfix) with ESMTPA id E32356005C; Wed, 20 Jan 2021 05:42:49 +0000 (UTC) Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Subject: Re: [PATCH v3 1/8] powerpc/uaccess: Add unsafe_copy_from_user From: "Christopher M. Riedl" To: "Christophe Leroy" , "Michael Ellerman" , Date: Tue, 19 Jan 2021 23:08:03 -0600 Message-Id: In-Reply-To: <1e6309a4-58fe-c6a4-6e47-d8659177846c@csgroup.eu> X-Virus-Scanned: ClamAV using ClamSMTP 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: , Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue Jan 19, 2021 at 11:27 AM CST, Christophe Leroy wrote: > > > Le 19/01/2021 =C3=A0 18:02, Christopher M. Riedl a =C3=A9crit : > > On Tue Jan 19, 2021 at 6:33 AM CST, Christophe Leroy wrote: > >> > >> > >> Le 19/01/2021 =C3=A0 03:11, Michael Ellerman a =C3=A9crit : > >>> "Christopher M. Riedl" writes: > >>>> On Mon Jan 11, 2021 at 7:22 AM CST, Christophe Leroy wrote: > >>>>> Le 09/01/2021 =C3=A0 04:25, Christopher M. Riedl a =C3=A9crit : > >>>>>> Implement raw_copy_from_user_allowed() which assumes that userspac= e read > >>>>>> access is open. Use this new function to implement raw_copy_from_u= ser(). > >>>>>> Finally, wrap the new function to follow the usual "unsafe_" conve= ntion > >>>>>> of taking a label argument. > >>>>> > >>>>> I think there is no point implementing raw_copy_from_user_allowed()= , see > >>>>> https://github.com/linuxppc/linux/commit/4b842e4e25b1 and > >>>>> https://patchwork.ozlabs.org/project/linuxppc-dev/patch/8c74fc9ce81= 31cabb10b3e95dc0e430f396ee83e.1610369143.git.christophe.leroy@csgroup.eu/ > >>>>> > >>>>> You should simply do: > >>>>> > >>>>> #define unsafe_copy_from_user(d, s, l, e) \ > >>>>> unsafe_op_wrap(__copy_tofrom_user((__force void __user *)d, s, l), = e) > >>>>> > >>>> > >>>> I gave this a try and the signal ops decreased by ~8K. Now, to be > >>>> honest, I am not sure what an "acceptable" benchmark number here > >>>> actually is - so maybe this is ok? Same loss with both radix and has= h: > >>>> > >>>> | | hash | radix | > >>>> | ------------------------------------ | ------ | ------ | > >>>> | linuxppc/next | 118693 | 133296 | > >>>> | linuxppc/next w/o KUAP+KUEP | 228911 | 228654 | > >>>> | unsafe-signal64 | 200480 | 234067 | > >>>> | unsafe-signal64 (__copy_tofrom_user) | 192467 | 225119 | > >>>> > >>>> To put this into perspective, prior to KUAP and uaccess flush, signa= l > >>>> performance in this benchmark was ~290K on hash. > >>> > >>> If I'm doing the math right 8K is ~4% of the best number. > >>> > >>> It seems like 4% is worth a few lines of code to handle these constan= t > >>> sizes. It's not like we have performance to throw away. > >>> > >>> Or, we should chase down where the call sites are that are doing smal= l > >>> constant copies with copy_to/from_user() and change them to use > >>> get/put_user(). > >>> > >> > >> Christopher, when you say you gave it a try, is I my series or only th= e > >> following ? > >> > >> #define unsafe_copy_from_user(d, s, l, e) \ > >> unsafe_op_wrap(__copy_tofrom_user((__force void __user *)d, s, l), e) > >> > >=20 > > I only used the above to replace this patch in my series (so none of my > > changes implementing raw_copy_from_user_allowed() are included). > > Then I see no reason why the performance would be different, because you > only call > unsafe_copy_from_user() with non trivial lengthes. > Ok I made a mistake - this actually included the other improvements from your feedback on this series; specifically moving the unsafe_get_user() call to read the msr regs value into the #ifdef. My first pass resulted in another __get_user() call which explains some of the perf loss. With that mistake fixed, the benchmark performance is still only ~197k on hash (consistent). I agree that there are no places where unsafe_copy_from_user() is called with trivial lengths so the only conclusion I can draw is that the changes in this patch marginally speed-up the other __copy_from_user() calls. I started comparing the disassembly but nothing immediately obvious stands out to me. In fact, I observe the speed-up even if I keep this patch _and_ apply this change: #define unsafe_copy_from_user(d, s, l, e) \ unsafe_op_wrap(__copy_tofrom_user((__force void __user *)d, s, l), e) Related to that, I think sigset_t is always 8B on ppc64 so these will probably need a wrapper if we pick-up your series to get rid of trivial size optimizations: __copy_from_user(&set, &uc->uc_sigmask, sizeof(set)) I can bring performance up to ~200K on hash again by replacing the two __copy_from_user(&set, ...) with direct calls to __get_user_size() (it's kind of hacky I think). See the last commit in this tree: https://git.sr.ht/~cmr/linux/log/unsafe-signal64-v4 All my comments apply to performance on radix as well. > >=20 > >> > >> Because I see no use of unsafe_copy_from_user() that would explain tha= t. > >> > >> Christophe