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,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 E6608C433ED for ; Tue, 13 Apr 2021 10:36:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BFE0B61278 for ; Tue, 13 Apr 2021 10:36:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245446AbhDMKhM convert rfc822-to-8bit (ORCPT ); Tue, 13 Apr 2021 06:37:12 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:22620 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245151AbhDMKhL (ORCPT ); Tue, 13 Apr 2021 06:37:11 -0400 Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-35-nVjCyOMmNoSV_7KKXm-MGA-1; Tue, 13 Apr 2021 11:36:49 +0100 X-MC-Unique: nVjCyOMmNoSV_7KKXm-MGA-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Tue, 13 Apr 2021 11:36:48 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.012; Tue, 13 Apr 2021 11:36:48 +0100 From: David Laight To: 'Peter Zijlstra' , Eric Dumazet CC: Ingo Molnar , Mathieu Desnoyers , "Paul E . McKenney" , Boqun Feng , Arjun Roy , linux-kernel , Eric Dumazet Subject: RE: [PATCH 3/3] rseq: optimise for 64bit arches Thread-Topic: [PATCH 3/3] rseq: optimise for 64bit arches Thread-Index: AQHXMETc4NN4/ddyHEK6qBKOxo8eAaqyQOlA Date: Tue, 13 Apr 2021 10:36:48 +0000 Message-ID: References: <20210413073657.2308450-1-eric.dumazet@gmail.com> <20210413073657.2308450-4-eric.dumazet@gmail.com> In-Reply-To: Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Peter Zijlstra > Sent: 13 April 2021 10:10 > > On Tue, Apr 13, 2021 at 12:36:57AM -0700, Eric Dumazet wrote: > > From: Eric Dumazet > > > > Commit ec9c82e03a74 ("rseq: uapi: Declare rseq_cs field as union, > > update includes") added regressions for our servers. > > > > Using copy_from_user() and clear_user() for 64bit values > > on 64bit arches is suboptimal. > > > > We might revisit this patch once all 32bit arches support > > get_user() and/or put_user() for 8 bytes values. > > Argh, what a mess :/ afaict only nios32 lacks put_user_8, but get_user_8 > is missing in a fair number of archs. > > That said; 32bit archs never have to actually set the top bits in that > word, so they _could_ only set the low 32 bits. That works provided > userspace itself keeps the high bits clear. Does that work for 32bit BE ? David > So I suppose that if we're going to #ifdef this, we might as well do the > whole thing. > > Mathieu; did I forget a reason why this cannot work? > > diff --git a/kernel/rseq.c b/kernel/rseq.c > index a4f86a9d6937..94006190b8eb 100644 > --- a/kernel/rseq.c > +++ b/kernel/rseq.c > @@ -115,20 +115,25 @@ static int rseq_reset_rseq_cpu_id(struct task_struct *t) > static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs) > { > struct rseq_cs __user *urseq_cs; > - u64 ptr; > + unsigned long ptr; > u32 __user *usig; > u32 sig; > int ret; > > - if (copy_from_user(&ptr, &t->rseq->rseq_cs.ptr64, sizeof(ptr))) > +#ifdef CONFIG_64BIT > + if (get_user(ptr, &t->rseq->rseq_cs.ptr64)) > return -EFAULT; > +#else > + if (get_user(ptr, &t->rseq->rseq_cs.ptr32)) > + return -EFAULT; > +#endif > if (!ptr) { > memset(rseq_cs, 0, sizeof(*rseq_cs)); > return 0; > } > if (ptr >= TASK_SIZE) > return -EINVAL; > - urseq_cs = (struct rseq_cs __user *)(unsigned long)ptr; > + urseq_cs = (struct rseq_cs __user *)ptr; > if (copy_from_user(rseq_cs, urseq_cs, sizeof(*rseq_cs))) > return -EFAULT; > - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)