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=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,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 D2FEEC433B4 for ; Tue, 13 Apr 2021 16:54:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B13A06128C for ; Tue, 13 Apr 2021 16:54:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346928AbhDMQzI (ORCPT ); Tue, 13 Apr 2021 12:55:08 -0400 Received: from mail.efficios.com ([167.114.26.124]:55802 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231909AbhDMQzH (ORCPT ); Tue, 13 Apr 2021 12:55:07 -0400 Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id 402BC339BE6; Tue, 13 Apr 2021 12:54:47 -0400 (EDT) Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id WSEUydMmTHtt; Tue, 13 Apr 2021 12:54:45 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id 8E3A6339C74; Tue, 13 Apr 2021 12:54:45 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 8E3A6339C74 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1618332885; bh=19r8E9l+nNtb+foE6hIEANruyXZGmyX4i3IECUfrxmA=; h=Date:From:To:Message-ID:MIME-Version; b=RW0dSyPNY1QcYmrJPeU/gBXpB2gWJMXEPomOS+fZ7aeBnqK8X6TN9Ct0I7rdv8zVf Mth1fRxgMrHYZnzLbbRFikbUw8lh4p4vcJgvCWJOuB7uy/faxowNBwAqg4J1qm7X7V YqYfDHtJvbn8Ms0ZHWxqh430qhXm9ja07TB08fCx5Xp698cjp5XvmDtz/XN01ux6pd XfHHRt+NDYVXfAwLjO32rm998j8TTzFYTCxbbV6kfT+3PyB3Ra7B1smWZcvsiivr1C 1duLm5QvRnrIaEcN1CQE0JSo5vUxMiAkCIC0C1n1oWWdy/lzAI44zTgs3C2BMSZozO 7CdxoFve70DYA== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id 0Oz4F5x51s9S; Tue, 13 Apr 2021 12:54:45 -0400 (EDT) Received: from mail03.efficios.com (mail03.efficios.com [167.114.26.124]) by mail.efficios.com (Postfix) with ESMTP id 7B540339DB2; Tue, 13 Apr 2021 12:54:45 -0400 (EDT) Date: Tue, 13 Apr 2021 12:54:45 -0400 (EDT) From: Mathieu Desnoyers To: Eric Dumazet , David Laight Cc: Ingo Molnar , Peter Zijlstra , paulmck , Boqun Feng , Arjun Roy , linux-kernel , Eric Dumazet Message-ID: <567941475.72456.1618332885342.JavaMail.zimbra@efficios.com> In-Reply-To: <20210413162240.3131033-4-eric.dumazet@gmail.com> References: <20210413162240.3131033-1-eric.dumazet@gmail.com> <20210413162240.3131033-4-eric.dumazet@gmail.com> Subject: Re: [PATCH v2 3/3] rseq: optimise rseq_get_rseq_cs() and clear_rseq_cs() MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.26.124] X-Mailer: Zimbra 8.8.15_GA_3996 (ZimbraWebClient - FF87 (Linux)/8.8.15_GA_4007) Thread-Topic: rseq: optimise rseq_get_rseq_cs() and clear_rseq_cs() Thread-Index: W0pbtVW2B+w+tUTMTDDH34Aw1yg2aQ== Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Apr 13, 2021, at 12:22 PM, Eric Dumazet eric.dumazet@gmail.com 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 > is suboptimal. > > We can use faster put_user() and get_user(). > > 32bit arches can be changed to use the ptr32 field, > since the padding field must always be zero. > > v2: added ideas from Peter and Mathieu about making this > generic, since my initial patch was only dealing with > 64bit arches. Ah, now I remember the reason why reading and clearing the entire 64-bit is important: it's because we don't want to allow user-space processes to use this change in behavior to figure out whether they are running on a 32-bit or in a 32-bit compat mode on a 64-bit kernel. So although I'm fine with making 64-bit kernels faster, we'll want to keep updating the entire 64-bit ptr field on 32-bit kernels as well. Thanks, Mathieu > > Signed-off-by: Eric Dumazet > Cc: Mathieu Desnoyers > Cc: Peter Zijlstra > Cc: "Paul E. McKenney" > Cc: Boqun Feng > Cc: Arjun Roy > Cc: Ingo Molnar > --- > kernel/rseq.c | 41 +++++++++++++++++++++++++++++++++-------- > 1 file changed, 33 insertions(+), 8 deletions(-) > > diff --git a/kernel/rseq.c b/kernel/rseq.c > index > cfe01ab5253c1c424c0e8b25acbb6a8e1b41a5b6..f2eee3f7f5d330688c81cb2e57d47ca6b843873e > 100644 > --- a/kernel/rseq.c > +++ b/kernel/rseq.c > @@ -119,23 +119,46 @@ static int rseq_reset_rseq_cpu_id(struct task_struct *t) > return 0; > } > > +#ifdef CONFIG_64BIT > +static int rseq_get_cs_ptr(struct rseq_cs __user **uptrp, > + const struct rseq __user *rseq) > +{ > + u64 ptr; > + > + if (get_user(ptr, &rseq->rseq_cs.ptr64)) > + return -EFAULT; > + *uptrp = (struct rseq_cs __user *)ptr; > + return 0; > +} > +#else > +static int rseq_get_cs_ptr(struct rseq_cs __user **uptrp, > + const struct rseq __user *rseq) > +{ > + u32 ptr; > + > + if (get_user(ptr, &rseq->rseq_cs.ptr.ptr32)) > + return -EFAULT; > + *uptrp = (struct rseq_cs __user *)ptr; > + return 0; > +} > +#endif > + > static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs) > { > struct rseq_cs __user *urseq_cs; > - u64 ptr; > u32 __user *usig; > u32 sig; > int ret; > > - if (copy_from_user(&ptr, &t->rseq->rseq_cs.ptr64, sizeof(ptr))) > + if (rseq_get_cs_ptr(&urseq_cs, t->rseq)) > return -EFAULT; > - if (!ptr) { > + if (!urseq_cs) { > memset(rseq_cs, 0, sizeof(*rseq_cs)); > return 0; > } > - if (ptr >= TASK_SIZE) > + if ((unsigned long)urseq_cs >= TASK_SIZE) > return -EINVAL; > - urseq_cs = (struct rseq_cs __user *)(unsigned long)ptr; > + > if (copy_from_user(rseq_cs, urseq_cs, sizeof(*rseq_cs))) > return -EFAULT; > > @@ -211,9 +234,11 @@ static int clear_rseq_cs(struct task_struct *t) > * > * Set rseq_cs to NULL. > */ > - if (clear_user(&t->rseq->rseq_cs.ptr64, sizeof(t->rseq->rseq_cs.ptr64))) > - return -EFAULT; > - return 0; > +#ifdef CONFIG_64BIT > + return put_user(0UL, &t->rseq->rseq_cs.ptr64); > +#else > + return put_user(0UL, &t->rseq->rseq_cs.ptr.ptr32); > +#endif > } > > /* > -- > 2.31.1.295.g9ea45b61b8-goog -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com