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=-3.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 7EC0FC4361B for ; Wed, 9 Dec 2020 13:28:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5157723B45 for ; Wed, 9 Dec 2020 13:28:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732384AbgLIN2d (ORCPT ); Wed, 9 Dec 2020 08:28:33 -0500 Received: from foss.arm.com ([217.140.110.172]:34654 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732358AbgLIN2G (ORCPT ); Wed, 9 Dec 2020 08:28:06 -0500 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 6032831B; Wed, 9 Dec 2020 05:27:20 -0800 (PST) Received: from C02TD0UTHF1T.local (unknown [10.57.26.40]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2F7983F66B; Wed, 9 Dec 2020 05:27:17 -0800 (PST) Date: Wed, 9 Dec 2020 13:27:10 +0000 From: Mark Rutland To: Andy Lutomirski Cc: =?utf-8?B?SsO8cmdlbiBHcm/Dnw==?= , Peter Zijlstra , Stefano Stabellini , "VMware, Inc." , X86 ML , LKML , Linux Virtualization , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , xen-devel , Thomas Gleixner , Boris Ostrovsky Subject: Re: [PATCH v2 05/12] x86: rework arch_local_irq_restore() to not use popf Message-ID: <20201209132710.GA8566@C02TD0UTHF1T.local> References: <20201120114630.13552-1-jgross@suse.com> <20201120114630.13552-6-jgross@suse.com> <20201120115943.GD3021@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Nov 22, 2020 at 01:44:53PM -0800, Andy Lutomirski wrote: > On Sat, Nov 21, 2020 at 10:55 PM Jürgen Groß wrote: > > > > On 20.11.20 12:59, Peter Zijlstra wrote: > > > On Fri, Nov 20, 2020 at 12:46:23PM +0100, Juergen Gross wrote: > > >> +static __always_inline void arch_local_irq_restore(unsigned long flags) > > >> +{ > > >> + if (!arch_irqs_disabled_flags(flags)) > > >> + arch_local_irq_enable(); > > >> +} > > > > > > If someone were to write horrible code like: > > > > > > local_irq_disable(); > > > local_irq_save(flags); > > > local_irq_enable(); > > > local_irq_restore(flags); > > > > > > we'd be up some creek without a paddle... now I don't _think_ we have > > > genius code like that, but I'd feel saver if we can haz an assertion in > > > there somewhere... > > > > > > Maybe something like: > > > > > > #ifdef CONFIG_DEBUG_ENTRY // for lack of something saner > > > WARN_ON_ONCE((arch_local_save_flags() ^ flags) & X86_EFLAGS_IF); > > > #endif > > > > > > At the end? > > > > I'd like to, but using WARN_ON_ONCE() in include/asm/irqflags.h sounds > > like a perfect receipt for include dependency hell. > > > > We could use a plain asm("ud2") instead. > > How about out-of-lining it: > > #ifdef CONFIG_DEBUG_ENTRY > extern void warn_bogus_irqrestore(); > #endif > > static __always_inline void arch_local_irq_restore(unsigned long flags) > { > if (!arch_irqs_disabled_flags(flags)) { > arch_local_irq_enable(); > } else { > #ifdef CONFIG_DEBUG_ENTRY > if (unlikely(arch_local_irq_save() & X86_EFLAGS_IF)) > warn_bogus_irqrestore(); > #endif > } I was just talking to Peter on IRC about implementing the same thing for arm64, so could we put this in the generic irqflags code? IIUC we can use raw_irqs_disabled() to do the check. As this isn't really entry specific (and IIUC the cases this should catch would break lockdep today), maybe we should add a new DEBUG_IRQFLAGS for this, that DEBUG_LOCKDEP can also select? Something like: #define local_irq_restore(flags) \ do { \ if (!raw_irqs_disabled_flags(flags)) { \ trace_hardirqs_on(); \ } else if (IS_ENABLED(CONFIG_DEBUG_IRQFLAGS) { \ if (unlikely(raw_irqs_disabled()) \ warn_bogus_irqrestore(); \ } \ raw_local_irq_restore(flags); \ } while (0) ... perhaps? (ignoring however we deal with once-ness). Thanks, Mark.