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_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 D3432C433E0 for ; Thu, 21 May 2020 10:45:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A579D207FB for ; Thu, 21 May 2020 10:45:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727978AbgEUKp6 (ORCPT ); Thu, 21 May 2020 06:45:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48282 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727013AbgEUKp5 (ORCPT ); Thu, 21 May 2020 06:45:57 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0FE35C061A0E for ; Thu, 21 May 2020 03:45:57 -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 1jbihP-0006pf-UO; Thu, 21 May 2020 12:45:16 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id C639B100C2D; Thu, 21 May 2020 12:45:14 +0200 (CEST) From: Thomas Gleixner To: Andy Lutomirski Cc: Andy Lutomirski , Andrew Cooper , LKML , X86 ML , "Paul E. McKenney" , 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 , Tom Lendacky , Wei Liu , Michael Kelley , Jason Chen CJ , Zhao Yakui , "Peter Zijlstra \(Intel\)" Subject: Re: [patch V6 10/37] x86/entry: Switch XEN/PV hypercall entry to IDTENTRY In-Reply-To: References: <20200515234547.710474468@linutronix.de> <20200515235125.425810667@linutronix.de> <87imgr7nwp.fsf@nanos.tec.linutronix.de> <87y2pm4ruh.fsf@nanos.tec.linutronix.de> <871rnewh5w.fsf@nanos.tec.linutronix.de> Date: Thu, 21 May 2020 12:45:14 +0200 Message-ID: <87wo55tvlx.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: > On Wed, May 20, 2020 at 12:17 PM Thomas Gleixner wrote: >> >> Andy Lutomirski writes: >> > Andrew Cooper pointed out that there is too much magic in Xen for this >> > to work. So never mind. >> >> :) >> >> But you made me stare more at that stuff and I came up with a way >> simpler solution. See below. > > I like it, but I bet it can be even simpler if you do the > tickle_whatever_paulmck_call_it() change: > >> +__visible noinstr void xen_pv_evtchn_do_upcall(struct pt_regs *regs) >> +{ >> + struct pt_regs *old_regs; >> + bool inhcall; >> + >> + idtentry_enter(regs); >> + old_regs = set_irq_regs(regs); >> + >> + run_on_irqstack(__xen_pv_evtchn_do_upcall, NULL, regs); >> + >> + set_irq_regs(old_regs); >> + >> + inhcall = get_and_clear_inhcall(); >> + __idtentry_exit(regs, inhcall); >> + restore_inhcall(inhcall); > > How about: > > inhcall = get_and_clear_inhcall(); > if (inhcall) { > if (!WARN_ON_ONCE((regs->flags & X86_EFLAGS_IF) || preempt_count()) { > local_irq_enable(); > cond_resched(); > local_irq_disable(); This really want's to use preempt_schedule_irq() as the above is racy vs. need_resched(). > } > } > restore_inhcall(inhcall); > idtentry_exit(regs); > > This could probably be tidied up by having a xen_maybe_preempt() that > does the inhcall and resched mess. > > The point is that, with the tickle_nohz_ stuff, there is nothing > actually preventing IRQ handlers from sleeping as long as they aren't > on the IRQ stack and as long as the interrupted context was safe to > sleep in. You still lose the debug checks. I'm working on it ... Thanks, tglx