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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 9CCAAC3A5A2 for ; Fri, 20 Sep 2019 14:29:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7487F207E0 for ; Fri, 20 Sep 2019 14:29:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390431AbfITO31 (ORCPT ); Fri, 20 Sep 2019 10:29:27 -0400 Received: from foss.arm.com ([217.140.110.172]:45584 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389000AbfITO3Z (ORCPT ); Fri, 20 Sep 2019 10:29:25 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 5C5B5337; Fri, 20 Sep 2019 07:29:24 -0700 (PDT) Received: from arrakis.emea.arm.com (arrakis.cambridge.arm.com [10.1.196.78]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E188E3F67D; Fri, 20 Sep 2019 07:29:22 -0700 (PDT) Date: Fri, 20 Sep 2019 15:29:20 +0100 From: Catalin Marinas To: Thomas Gleixner Cc: LKML , x86@kernel.org, Peter Zijlstra , Andy Lutomirski , Will Deacon , Mark Rutland , Marc Zyngier , Paolo Bonzini , kvm@vger.kernel.org, linux-arch@vger.kernel.org Subject: Re: [RFC patch 07/15] arm64/syscall: Remove obscure flag check Message-ID: <20190920142920.GB21231@arrakis.emea.arm.com> References: <20190919150314.054351477@linutronix.de> <20190919150809.145400160@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190919150809.145400160@linutronix.de> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 19, 2019 at 05:03:21PM +0200, Thomas Gleixner wrote: > The syscall handling code has an obscure check of pending work which does a > shortcut before returning to user space. It calls into the exit work code > when the flags at entry time required an entry into the slowpath. That does > not make sense because the underlying work functionality will reevaluate > the flags anyway and not do anything. The current C code was just matching the original behaviour in asm (converted by commit f37099b6992a0b81). The idea IIRC was to always pair a syscall_trace_enter() with a syscall_trace_exit() irrespective of the thread flag changes. I think the behaviour is preserved with your patch if no-one clears the work flags during el0_svc_common(). > @@ -105,33 +103,15 @@ static void el0_svc_common(struct pt_reg > user_exit(); > > scno = syscall_enter_from_usermode(regs, scno); > - if (scno == NO_SYSCALL) > - goto trace_exit; > - > - invoke_syscall(regs, scno, sc_nr, syscall_table); > + if (scno != NO_SYSCALL) > + invoke_syscall(regs, scno, sc_nr, syscall_table); > > - /* > - * The tracing status may have changed under our feet, so we have to > - * check again. However, if we were tracing entry, then we always trace > - * exit regardless, as the old entry assembly did. > - */ > - if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) { > - local_daif_mask(); > - flags = current_thread_info()->flags; > - if (!has_syscall_work(flags)) { > - /* > - * We're off to userspace, where interrupts are > - * always enabled after we restore the flags from > - * the SPSR. > - */ > - trace_hardirqs_on(); > - return; > - } > + local_daif_mask(); > + if (has_syscall_work(current_thread_info()->flags) || > + IS_ENABLED(CONFIG_DEBUG_RSEQ)) { > local_daif_restore(DAIF_PROCCTX); > + syscall_trace_exit(regs); > } That's missing a trace_hardirqs_on() (off done in local_daif_mask()) before returning. > - > -trace_exit: > - syscall_trace_exit(regs); > } -- Catalin