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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 3CCDFC11D2F for ; Mon, 24 Feb 2020 16:34:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 119DD2080D for ; Mon, 24 Feb 2020 16:34:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="MXxp49h1" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728035AbgBXQee (ORCPT ); Mon, 24 Feb 2020 11:34:34 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:34964 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727299AbgBXQee (ORCPT ); Mon, 24 Feb 2020 11:34:34 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=M9yl3DP9ucs4uObZLy5iqNZp2w5Oe3v/bojnGtEYlbQ=; b=MXxp49h1d8mC9C7ommRJDgNBg2 wpKAI81DLo1i64lQCugUzdwQycxvzgFZ6U1ieomQy7t/y+0i/eg9+QGcWjdlFUVTwTsZ+loAjfQL9 kwA2oeX/gkS4E3vhclr++JkVYwPasd1TuYViTEC3VX6pDL9S6CDzlcJT5ynjNFl5Q6clD8NilTrdT qErRR5aXXXwqXAlyuMPvlf8MFKRNHaXd3mRCYW0/UUGAg96OJGYEQw73S22k3Xx75P/Yp2pfoBi6u UApcmr/PU89uYMAqBLAEJi3+2vGbUpGhKGlDQW5GtMNxRBVH8FwpQzEczySgu8VoBekplb1p45twD VkCVDaGg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1j6GgN-0003n0-S5; Mon, 24 Feb 2020 16:34:12 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 4C6C6305EFE; Mon, 24 Feb 2020 17:32:15 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id CA7B4202BD153; Mon, 24 Feb 2020 17:34:09 +0100 (CET) Date: Mon, 24 Feb 2020 17:34:09 +0100 From: Peter Zijlstra To: Steven Rostedt Cc: Andy Lutomirski , LKML , linux-arch , Ingo Molnar , Joel Fernandes , Greg KH , gustavo@embeddedor.com, Thomas Gleixner , paulmck@kernel.org, Josh Triplett , Mathieu Desnoyers , Lai Jiangshan , Tony Luck , Frederic Weisbecker , Dan Carpenter , Masami Hiramatsu Subject: Re: [PATCH v4 05/27] x86: Replace ist_enter() with nmi_enter() Message-ID: <20200224163409.GJ18400@hirez.programming.kicks-ass.net> References: <20200221133416.777099322@infradead.org> <20200221134215.328642621@infradead.org> <20200221202246.GA14897@hirez.programming.kicks-ass.net> <20200224104346.GJ14946@hirez.programming.kicks-ass.net> <20200224112708.4f307ba3@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200224112708.4f307ba3@gandalf.local.home> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 24, 2020 at 11:27:08AM -0500, Steven Rostedt wrote: > On Mon, 24 Feb 2020 11:43:46 +0100 > Peter Zijlstra wrote: > > > -dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code) > > +dotraplinkage notrace void do_int3(struct pt_regs *regs, long error_code) > > { > > if (poke_int3_handler(regs)) > > return; > > > > /* > > - * Use ist_enter despite the fact that we don't use an IST stack. > > - * We can be called from a kprobe in non-CONTEXT_KERNEL kernel > > - * mode or even during context tracking state changes. > > - * > > - * This means that we can't schedule. That's okay. > > + * Unlike any other non-IST entry, we can be called from pretty much > > + * any location in the kernel through kprobes -- text_poke() will most > > + * likely be handled by poke_int3_handler() above. This means this > > + * handler is effectively NMI-like. > > */ > > - ist_enter(regs); > > + nmi_enter(); > > Hmm, note that nmi_enter() calls other functions. Did you make sure > all of them are not able to be kprobed. This is different than just > being "NMI like", it's that if they are kprobed, then this will go into > an infinite loop because nothing can have a kprobe before the kprobe > int3 handler is called here. I did not audit that; I went with the fact that hitting kprobes before in_nmi() is true is a bug. Looking at nmi_enter(), that leaves trace_hardirq_enter(), since we know we marked rcu_nmi_enter() as NOKPROBES, per the patches elsewhere in this series.