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,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 27547C433DF for ; Wed, 20 May 2020 15:27:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EF9C9206BE for ; Wed, 20 May 2020 15:27:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726805AbgETP1m (ORCPT ); Wed, 20 May 2020 11:27:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37094 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726436AbgETP1l (ORCPT ); Wed, 20 May 2020 11:27:41 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B031AC061A0E for ; Wed, 20 May 2020 08:27:41 -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 1jbQcj-0004FE-Bq; Wed, 20 May 2020 17:27:13 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id AF656100C99; Wed, 20 May 2020 17:27:12 +0200 (CEST) From: Thomas Gleixner To: Andy Lutomirski Cc: Andy Lutomirski , 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 07/37] x86/entry: Provide helpers for execute on irqstack In-Reply-To: References: <20200515234547.710474468@linutronix.de> <20200515235125.110889386@linutronix.de> <87o8qkvm03.fsf@nanos.tec.linutronix.de> <871rne6ayr.fsf@nanos.tec.linutronix.de> Date: Wed, 20 May 2020 17:27:12 +0200 Message-ID: <87d06ywrsf.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 5:35 AM Thomas Gleixner wrote: >> >> Andy Lutomirski writes: >> > On Mon, May 18, 2020 at 4:53 PM Thomas Gleixner wrote: >> >> >> >> Andy Lutomirski writes: >> >> > Actually, I revoke my ack. Can you make one of two changes: >> >> > >> >> > Option A: Add an assertion to run_on_irqstack to verify that irq_count >> >> > was -1 at the beginning? I suppose this also means you could just >> >> > explicitly write 0 instead of adding and subtracting. >> >> > >> >> > Option B: Make run_on_irqstack() just call the function on the current >> >> > stack if we're already on the irq stack. >> >> > >> >> > Right now, it's too easy to mess up and not verify the right >> >> > precondition before calling run_on_irqstack(). >> >> > >> >> > If you choose A, perhaps add a helper to do the if(irq_needs_irqstack) >> >> > dance so that users can just do: >> >> > >> >> > run_on_irqstack_if_needed(...); >> >> > >> >> > instead of checking everything themselves. >> >> >> >> I'll have a look tomorrow morning with brain awake. >> > >> > Also, reading more of the series, I suspect that asm_call_on_stack is >> > logically in the wrong section or that the noinstr stuff is otherwise >> > not quite right. I think that objtool should not accept >> > run_on_irqstack() from noinstr code. See followups on patch 10. >> >> It's in entry.text which is non-instrumentable as well. > > Hmm. I suppose we can chalk this up to the noinstr checking not being > entirely perfect. objtool considers both entry.text and noinstr.text. We just can't stick everything into entry.text for these !%@#45@# reasons.