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=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,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 86EC7C5519F for ; Sun, 22 Nov 2020 21:45:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 443922074B for ; Sun, 22 Nov 2020 21:45:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="1ywLGw0S" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726315AbgKVVpL (ORCPT ); Sun, 22 Nov 2020 16:45:11 -0500 Received: from mail.kernel.org ([198.145.29.99]:57714 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725782AbgKVVpK (ORCPT ); Sun, 22 Nov 2020 16:45:10 -0500 Received: from mail-wm1-f48.google.com (mail-wm1-f48.google.com [209.85.128.48]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id BEBF020789 for ; Sun, 22 Nov 2020 21:45:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1606081510; bh=j8kQr1sqydOsvjEY9shLB0wmUrzUic9iCe1dNmPahV0=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=1ywLGw0S6Iag6+okOvBgPfWDSIRAX+z1ZSr78Si08frRCT6wlTaFGPbwKtciUr39i O4G4Y6EDiAcTMD7bLatQqayiaSxXNnDjjohYDNfE1OGhJGilgriL+1Ok0nRavMxdql /HYOzGZTzKTS4GqAkezXaMALXqruwPPbUTcCQfII= Received: by mail-wm1-f48.google.com with SMTP id a3so15568446wmb.5 for ; Sun, 22 Nov 2020 13:45:09 -0800 (PST) X-Gm-Message-State: AOAM530pnjjhyKCqmkJP24uuC9JSuzQNdxa/JDM5ne2Ab52JFmKwXsDZ rRGjZn8FecKUS+S1amCTSwGscVfh6j+Ia6RcE9fytA== X-Google-Smtp-Source: ABdhPJwifakpgwUVTLbeDBYdoVmnAfRpiEVwGa2XrrCKUuyY/SYxT6I31Kv43oa6WFJkbjZ+4GFZn5n4pemXbXWt+C8= X-Received: by 2002:a1c:2781:: with SMTP id n123mr3937832wmn.49.1606081506352; Sun, 22 Nov 2020 13:45:06 -0800 (PST) MIME-Version: 1.0 References: <20201120114630.13552-1-jgross@suse.com> <20201120114630.13552-6-jgross@suse.com> <20201120115943.GD3021@hirez.programming.kicks-ass.net> In-Reply-To: From: Andy Lutomirski Date: Sun, 22 Nov 2020 13:44:53 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2 05/12] x86: rework arch_local_irq_restore() to not use popf To: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Cc: Peter Zijlstra , Stefano Stabellini , "VMware, Inc." , X86 ML , LKML , Linux Virtualization , Ingo Molnar , Borislav Petkov , Andrew Lutomirski , "H. Peter Anvin" , xen-devel , Thomas Gleixner , Boris Ostrovsky Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Nov 21, 2020 at 10:55 PM J=C3=BCrgen Gro=C3=9F wr= ote: > > 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 flag= s) > >> +{ > >> + 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 }