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=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,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 210CDC433E0 for ; Thu, 14 May 2020 17:46:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E0EB42053B for ; Thu, 14 May 2020 17:46:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="WVgk3epd" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726165AbgENRqM (ORCPT ); Thu, 14 May 2020 13:46:12 -0400 Received: from mail.efficios.com ([167.114.26.124]:39996 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725975AbgENRqL (ORCPT ); Thu, 14 May 2020 13:46:11 -0400 Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id B57B22A73BB; Thu, 14 May 2020 13:46:10 -0400 (EDT) Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id ftpm0gtnYq5x; Thu, 14 May 2020 13:46:10 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id 4BCBA2A7513; Thu, 14 May 2020 13:46:10 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 4BCBA2A7513 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1589478370; bh=/GdvTshxrvvhnSKnsBtmJtZGAFcFUSZomUuLaL/1Xdg=; h=Date:From:To:Message-ID:MIME-Version; b=WVgk3epdUF7Ha7sppoSPzh48s/EWqTGNJYcMJJnwSMuwRMNp8PlDnQBXGq/kSS+PN zaiCeuHW39fga28XonD6C6Zc5CAYVghexVjDDGSZk5GrgltVOszPXh9KTVigoNpmEQ mrXs2eBoInChlrlJ098ADx+gGceQS8DB4pZKqIHTvWzdOqtk4v8Ljq5I5q/PAAncH9 cXWjb38r/7ZAL87bxPooFpWgNDrg89mA2McvwZc11BCyT9N1UE0jOQZvgdkFAC19K5 XB3VKscPaR7l2bc+Gyzh1X6z+UB/3hxB+o+HpGjZd4EIGc13DrIHsWphZIEFGfC5/Y hptmr3Ma1U8TQ== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id UR_rARrfJ9-K; Thu, 14 May 2020 13:46:10 -0400 (EDT) Received: from mail03.efficios.com (mail03.efficios.com [167.114.26.124]) by mail.efficios.com (Postfix) with ESMTP id 365E12A6C7C; Thu, 14 May 2020 13:46:10 -0400 (EDT) Date: Thu, 14 May 2020 13:46:10 -0400 (EDT) From: Mathieu Desnoyers To: Thomas Gleixner Cc: linux-kernel , x86 , paulmck , Andy Lutomirski , Alexandre Chartre , Frederic Weisbecker , Paolo Bonzini , Sean Christopherson , Masami Hiramatsu , Petr Mladek , rostedt , "Joel Fernandes, Google" , Boris Ostrovsky , Juergen Gross , Brian Gerst , Josh Poimboeuf , Will Deacon , Peter Zijlstra Message-ID: <2107385142.21313.1589478370190.JavaMail.zimbra@efficios.com> In-Reply-To: <871rnmzarj.fsf@nanos.tec.linutronix.de> References: <20200505134926.578885807@linutronix.de> <20200505135314.808628211@linutronix.de> <552488029.20647.1589423096441.JavaMail.zimbra@efficios.com> <871rnmzarj.fsf@nanos.tec.linutronix.de> Subject: Re: [patch V4 part 4 15/24] x86/db: Split out dr6/7 handling MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.26.124] X-Mailer: Zimbra 8.8.15_GA_3928 (ZimbraWebClient - FF76 (Linux)/8.8.15_GA_3928) Thread-Topic: x86/db: Split out dr6/7 handling Thread-Index: oRKSde8vieHRNXPfgTJdj6DGkq1Icg== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On May 14, 2020, at 1:28 PM, Thomas Gleixner tglx@linutronix.de wrote: > Mathieu Desnoyers writes: >> ----- On May 5, 2020, at 9:49 AM, Thomas Gleixner tglx@linutronix.de wrote: >>> + >>> +static __always_inline void debug_exit(unsigned long dr7) >>> +{ >>> + set_debugreg(dr7, 7); >>> +} >> * Question 1 >> Out of curiosity, what prevents the compiler from moving instructions >> outside of the code regions surrounded by entry/exit ? This is an always >> inline, which invokes set_debugreg which is inline for CONFIG_PARAVIRT_XXL=n, >> which in turn uses an asm() (not volatile), without any memory >> clobber. >> ? * Question 2 >> Also, considering that "inline" is not sufficient to ensure the compiler >> does not emit a traceable function, I suspect you'll also want to mark >> "native_get_debugreg" and "native_set_debugreg" always inline as well. > > It can move it into a function and call that. Fine. If that function > stays in the noinstr section then it should not emit a trace stub and if > it moves it out of the section or reuses another instance in text then > objtool will complain. > > Checking for trace stubs and other instrumentation nonsense is on the > objtool wishlist anyway. > > But yes, marking these __always_inline prevents that. Those escaped my > chase. But I would have found them once I go and fix that paravirt muck. This answers only my second question (see "Question 1" above). Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com