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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 31C16C47255 for ; Mon, 11 May 2020 10:59:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 14A9F20736 for ; Mon, 11 May 2020 10:59:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729544AbgEKK7y (ORCPT ); Mon, 11 May 2020 06:59:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34806 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1728209AbgEKK7x (ORCPT ); Mon, 11 May 2020 06:59:53 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BDAABC061A0C for ; Mon, 11 May 2020 03:59:53 -0700 (PDT) Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jY69g-0003Hq-Eu; Mon, 11 May 2020 12:59:28 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id CCA98FFBF8; Mon, 11 May 2020 12:59:26 +0200 (CEST) From: Thomas Gleixner To: Andy Lutomirski Cc: LKML , X86 ML , "Paul E. McKenney" , Andy Lutomirski , Alexandre Chartre , Frederic Weisbecker , Paolo Bonzini , Sean Christopherson , Masami Hiramatsu , Petr Mladek , Steven Rostedt , Joel Fernandes , Boris Ostrovsky , Juergen Gross , Brian Gerst , Mathieu Desnoyers , Josh Poimboeuf , Will Deacon Subject: [patch V5 part 3 12/29] x86/entry/common: Provide idtentry_enter/exit() In-Reply-To: References: <20200505134354.774943181@linutronix.de> <20200505134904.457578656@linutronix.de> Date: Mon, 11 May 2020 12:59:26 +0200 Message-ID: <874ksm7n5d.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andy Lutomirski writes: >> + * Invoked by all exception/interrupt IDTENTRY handlers which are not >> + * returning through the paranoid exit path (all except NMI, #DF and the IST >> + * variants of #MC and #DB). > > The paranoid-exit bit is not really relevant. The important part is > which stack we're on. See below. Right. I amended the comment to that effect. >> + */ >> +void noinstr idtentry_exit(struct pt_regs *regs) >> +{ >> + lockdep_assert_irqs_disabled(); > > How about: > > #ifdef CONFIG_DEBUG_ENTRY > WARN_ON_ONCE(!on_thread_stack()); > #endif Made this if (IS_ENABLED()) .. >> + instr_begin(); >> + /* Tell the tracer that IRET will enable interrupts */ >> + trace_hardirqs_on_prepare(); > > Why is trace_hardirqs_on() okay above but not here? Is it that we > know we weren't RCU-quiescent if we had preemption and IF on? But > even this code path came from an IF-on context. I'm confused. Maybe > some comments as to why this case seems to be ordered so differently > from the !preempt_count() case would be helpful. Added commentry. Updated patch below. Thanks, tglx 8<----------------- Subject: x86/entry/common: Provide idtentry_enter/exit() From: Thomas Gleixner Date: Thu, 26 Mar 2020 16:28:52 +0100 Provide functions which handle the low level entry and exit similar to enter/exit from user mode. Signed-off-by: Thomas Gleixner --- arch/x86/entry/common.c | 100 ++++++++++++++++++++++++++++++++++++++++ arch/x86/include/asm/idtentry.h | 3 + 2 files changed, 103 insertions(+) --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -510,3 +510,103 @@ SYSCALL_DEFINE0(ni_syscall) { return -ENOSYS; } + +/** + * idtentry_enter - Handle state tracking on idtentry + * @regs: Pointer to pt_regs of interrupted context + * + * Invokes: + * - lockdep irqflag state tracking as low level ASM entry disabled + * interrupts. + * + * - Context tracking if the exception hit user mode. + * + * - RCU notification if the exception hit kernel mode + * + * - The hardirq tracer to keep the state consistent as low level ASM + * entry disabled interrupts. + */ +void noinstr idtentry_enter(struct pt_regs *regs) +{ + if (user_mode(regs)) { + enter_from_user_mode(); + } else { + lockdep_hardirqs_off(CALLER_ADDR0); + rcu_irq_enter(); + instrumentation_begin(); + trace_hardirqs_off_prepare(); + instrumentation_end(); + } +} + +/** + * idtentry_exit - Common code to handle return from exceptions + * @regs: Pointer to pt_regs (exception entry regs) + * + * Depending on the return target (kernel/user) this runs the necessary + * preemption and work checks if possible and required and returns to + * the caller with interrupts disabled and no further work pending. + * + * This is the last action before returning to the low level ASM code which + * just needs to return to the appropriate context. + * + * Invoked by all exception/interrupt IDTENTRY handlers which are not + * returning through the paranoid exit path (all except NMI, #DF and the IST + * variants of #MC and #DB) and are therefore on the thread stack. + */ +void noinstr idtentry_exit(struct pt_regs *regs) +{ + lockdep_assert_irqs_disabled(); + + if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) + WARN_ON_ONCE(!on_thread_stack()); + + /* Check whether this returns to user mode */ + if (user_mode(regs)) { + prepare_exit_to_usermode(regs); + } else if (regs->flags & X86_EFLAGS_IF) { + /* Check kernel preemption, if enabled */ + if (IS_ENABLED(CONFIG_PREEMPTION)) { + /* + * This needs to be done very carefully. + * idtentry_enter() invoked rcu_irq_enter(). This + * needs to undone before scheduling. + * + * Preemption is disabled inside of RCU idle + * sections. When the task returns from + * preempt_schedule_irq(), RCU is still watching. + * + * rcu_irq_exit_preempt() has additional state + * checking if CONFIG_PROVE_RCU=y + */ + if (!preempt_count()) { + instrumentation_begin(); + rcu_irq_exit_preempt(); + if (need_resched()) + preempt_schedule_irq(); + /* Covers both tracing and lockdep */ + trace_hardirqs_on(); + instrumentation_end(); + return; + } + } + /* + * If preemption is disabled then this needs to be done + * carefully with respect to RCU. The exception might come + * from a RCU idle section in the idle task due to the fact + * that safe_halt() enables interrupts. So this needs the + * same ordering of lockdep/tracing and RCU as the return + * to user mode path. + */ + instrumentation_begin(); + /* Tell the tracer that IRET will enable interrupts */ + trace_hardirqs_on_prepare(); + lockdep_hardirqs_on_prepare(CALLER_ADDR0); + instrumentation_end(); + rcu_irq_exit(); + lockdep_hardirqs_on(CALLER_ADDR0); + } else { + /* IRQ flags state is correct already. Just tell RCU */ + rcu_irq_exit(); + } +} --- a/arch/x86/include/asm/idtentry.h +++ b/arch/x86/include/asm/idtentry.h @@ -7,6 +7,9 @@ #ifndef __ASSEMBLY__ +void idtentry_enter(struct pt_regs *regs); +void idtentry_exit(struct pt_regs *regs); + /** * DECLARE_IDTENTRY - Declare functions for simple IDT entry points * No error code pushed by hardware