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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 D2446C3279B for ; Tue, 10 Jul 2018 20:23:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8C5E7208E5 for ; Tue, 10 Jul 2018 20:23:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8C5E7208E5 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=zytor.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732736AbeGJUYd (ORCPT ); Tue, 10 Jul 2018 16:24:33 -0400 Received: from terminus.zytor.com ([198.137.202.136]:34759 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732332AbeGJUYc (ORCPT ); Tue, 10 Jul 2018 16:24:32 -0400 Received: from terminus.zytor.com (localhost [127.0.0.1]) by terminus.zytor.com (8.15.2/8.15.2) with ESMTPS id w6AKN2qe3266469 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Tue, 10 Jul 2018 13:23:02 -0700 Received: (from tipbot@localhost) by terminus.zytor.com (8.15.2/8.15.2/Submit) id w6AKN1ma3266466; Tue, 10 Jul 2018 13:23:01 -0700 Date: Tue, 10 Jul 2018 13:23:01 -0700 X-Authentication-Warning: terminus.zytor.com: tipbot set sender to tipbot@zytor.com using -f From: tip-bot for Mathieu Desnoyers Message-ID: Cc: linux-kernel@vger.kernel.org, mtk.manpages@gmail.com, will.deacon@arm.com, joelaf@google.com, josh@joshtriplett.org, akpm@linux-foundation.org, boqun.feng@gmail.com, davejwatson@fb.com, peterz@infradead.org, cl@linux.com, bmaurer@fb.com, andi@firstfloor.org, mingo@kernel.org, tglx@linutronix.de, torvalds@linux-foundation.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, catalin.marinas@arm.com, linux@arm.linux.org.uk, hpa@zytor.com, pjt@google.com, luto@amacapital.net, paulmck@linux.vnet.ibm.com Reply-To: bmaurer@fb.com, cl@linux.com, andi@firstfloor.org, mingo@kernel.org, torvalds@linux-foundation.org, tglx@linutronix.de, akpm@linux-foundation.org, boqun.feng@gmail.com, davejwatson@fb.com, peterz@infradead.org, josh@joshtriplett.org, mtk.manpages@gmail.com, linux-kernel@vger.kernel.org, will.deacon@arm.com, joelaf@google.com, luto@amacapital.net, paulmck@linux.vnet.ibm.com, pjt@google.com, hpa@zytor.com, rostedt@goodmis.org, catalin.marinas@arm.com, mathieu.desnoyers@efficios.com, linux@arm.linux.org.uk In-Reply-To: <20180709195155.7654-4-mathieu.desnoyers@efficios.com> References: <20180709195155.7654-4-mathieu.desnoyers@efficios.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:core/urgent] rseq: uapi: Update uapi comments Git-Commit-ID: 0fb9a1abc8c97f858997e962694eb36b4517144e X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 0fb9a1abc8c97f858997e962694eb36b4517144e Gitweb: https://git.kernel.org/tip/0fb9a1abc8c97f858997e962694eb36b4517144e Author: Mathieu Desnoyers AuthorDate: Mon, 9 Jul 2018 15:51:52 -0400 Committer: Thomas Gleixner CommitDate: Tue, 10 Jul 2018 22:18:52 +0200 rseq: uapi: Update uapi comments Update rseq uapi header comments to reflect that user-space need to do thread-local loads/stores from/to the struct rseq fields. As a consequence of this added requirement, the kernel does not need to perform loads/stores with single-copy atomicity. Update the comment associated to the "flags" fields to describe more accurately that it's only useful to facilitate single-stepping through rseq critical sections with debuggers. Signed-off-by: Mathieu Desnoyers Signed-off-by: Thomas Gleixner Cc: linux-api@vger.kernel.org Cc: Peter Zijlstra Cc: "Paul E . McKenney" Cc: Boqun Feng Cc: Andy Lutomirski Cc: Dave Watson Cc: Paul Turner Cc: Andrew Morton Cc: Russell King Cc: "H . Peter Anvin" Cc: Andi Kleen Cc: Chris Lameter Cc: Ben Maurer Cc: Steven Rostedt Cc: Josh Triplett Cc: Linus Torvalds Cc: Catalin Marinas Cc: Will Deacon Cc: Michael Kerrisk Cc: Joel Fernandes Cc: "Paul E. McKenney" Cc: "H. Peter Anvin" Link: https://lkml.kernel.org/r/20180709195155.7654-4-mathieu.desnoyers@efficios.com --- include/uapi/linux/rseq.h | 69 ++++++++++++++++++++++++----------------------- kernel/rseq.c | 2 +- 2 files changed, 37 insertions(+), 34 deletions(-) diff --git a/include/uapi/linux/rseq.h b/include/uapi/linux/rseq.h index 519ad6e176d1..bf4188c13bec 100644 --- a/include/uapi/linux/rseq.h +++ b/include/uapi/linux/rseq.h @@ -67,28 +67,30 @@ struct rseq_cs { struct rseq { /* * Restartable sequences cpu_id_start field. Updated by the - * kernel, and read by user-space with single-copy atomicity - * semantics. Aligned on 32-bit. Always contains a value in the - * range of possible CPUs, although the value may not be the - * actual current CPU (e.g. if rseq is not initialized). This - * CPU number value should always be compared against the value - * of the cpu_id field before performing a rseq commit or - * returning a value read from a data structure indexed using - * the cpu_id_start value. + * kernel. Read by user-space with single-copy atomicity + * semantics. This field should only be read by the thread which + * registered this data structure. Aligned on 32-bit. Always + * contains a value in the range of possible CPUs, although the + * value may not be the actual current CPU (e.g. if rseq is not + * initialized). This CPU number value should always be compared + * against the value of the cpu_id field before performing a rseq + * commit or returning a value read from a data structure indexed + * using the cpu_id_start value. */ __u32 cpu_id_start; /* - * Restartable sequences cpu_id field. Updated by the kernel, - * and read by user-space with single-copy atomicity semantics. - * Aligned on 32-bit. Values RSEQ_CPU_ID_UNINITIALIZED and - * RSEQ_CPU_ID_REGISTRATION_FAILED have a special semantic: the - * former means "rseq uninitialized", and latter means "rseq - * initialization failed". This value is meant to be read within - * rseq critical sections and compared with the cpu_id_start - * value previously read, before performing the commit instruction, - * or read and compared with the cpu_id_start value before returning - * a value loaded from a data structure indexed using the - * cpu_id_start value. + * Restartable sequences cpu_id field. Updated by the kernel. + * Read by user-space with single-copy atomicity semantics. This + * field should only be read by the thread which registered this + * data structure. Aligned on 32-bit. Values + * RSEQ_CPU_ID_UNINITIALIZED and RSEQ_CPU_ID_REGISTRATION_FAILED + * have a special semantic: the former means "rseq uninitialized", + * and latter means "rseq initialization failed". This value is + * meant to be read within rseq critical sections and compared + * with the cpu_id_start value previously read, before performing + * the commit instruction, or read and compared with the + * cpu_id_start value before returning a value loaded from a data + * structure indexed using the cpu_id_start value. */ __u32 cpu_id; /* @@ -105,27 +107,28 @@ struct rseq { * targeted by the rseq_cs. Also needs to be set to NULL by user-space * before reclaiming memory that contains the targeted struct rseq_cs. * - * Read and set by the kernel with single-copy atomicity semantics. - * Set by user-space with single-copy atomicity semantics. Aligned - * on 64-bit. + * Read and set by the kernel. Set by user-space with single-copy + * atomicity semantics. This field should only be updated by the + * thread which registered this data structure. Aligned on 64-bit. */ LINUX_FIELD_u32_u64(rseq_cs); /* - * - RSEQ_DISABLE flag: + * Restartable sequences flags field. + * + * This field should only be updated by the thread which + * registered this data structure. Read by the kernel. + * Mainly used for single-stepping through rseq critical sections + * with debuggers. * - * Fallback fast-track flag for single-stepping. - * Set by user-space if lack of progress is detected. - * Cleared by user-space after rseq finish. - * Read by the kernel. * - RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT - * Inhibit instruction sequence block restart and event - * counter increment on preemption for this thread. + * Inhibit instruction sequence block restart on preemption + * for this thread. * - RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL - * Inhibit instruction sequence block restart and event - * counter increment on signal delivery for this thread. + * Inhibit instruction sequence block restart on signal + * delivery for this thread. * - RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE - * Inhibit instruction sequence block restart and event - * counter increment on migration for this thread. + * Inhibit instruction sequence block restart on migration for + * this thread. */ __u32 flags; } __attribute__((aligned(4 * sizeof(__u64)))); diff --git a/kernel/rseq.c b/kernel/rseq.c index 2c8463acb50d..2a7748675be7 100644 --- a/kernel/rseq.c +++ b/kernel/rseq.c @@ -201,7 +201,7 @@ static int clear_rseq_cs(struct task_struct *t) * of code outside of the rseq assembly block. This performs * a lazy clear of the rseq_cs field. * - * Set rseq_cs to NULL with single-copy atomicity. + * Set rseq_cs to NULL. */ return put_user(0UL, &t->rseq->rseq_cs); }