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=-7.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 99A37C35679 for ; Mon, 24 Feb 2020 10:44:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6BE6020732 for ; Mon, 24 Feb 2020 10:44:17 +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="pP7ckkOr" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727445AbgBXKoQ (ORCPT ); Mon, 24 Feb 2020 05:44:16 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:33670 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726509AbgBXKoQ (ORCPT ); Mon, 24 Feb 2020 05:44:16 -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=NdeRTgFFacaSdHt4nuX6tbLuXugUsK+Xct/DkGyNEjM=; b=pP7ckkOreRST4w3O2H8Ddh5czq FOgLeSwZ2T/7wIMWPVRzGIfiZYM/mtuIi+QFFVluts17heN/06s61qeHUQi3WFq9ptOEgX242J9Hb pnSqyZQ+x3DZU+mj6tG4xRr6cx9t/XYCli0L11/g421tVhqpdqI9g8gg09uxiZ5tu+943Fv3yX9Bl GOKK1YQcSrnY23yJKcjgnLe0v5zeibJVfHfOWQCsaeOYr+KXC9EJGDMPc9LESpn/ctHGSgSKfvE+G gXco9MQXlfNHRjLX5yms++w7KV4h2yPPlbDudXVXUTn85n8dOfhGu/mUeC3JiPiCCdQdjzFoKNQIi bCsTywVg==; 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 1j6BDI-0001nh-Sl; Mon, 24 Feb 2020 10:43:49 +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 0DB89300F7A; Mon, 24 Feb 2020 11:41:51 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 705CF29B4DB4E; Mon, 24 Feb 2020 11:43:46 +0100 (CET) Date: Mon, 24 Feb 2020 11:43:46 +0100 From: Peter Zijlstra To: Andy Lutomirski Cc: LKML , linux-arch , Steven Rostedt , 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: <20200224104346.GJ14946@hirez.programming.kicks-ass.net> References: <20200221133416.777099322@infradead.org> <20200221134215.328642621@infradead.org> <20200221202246.GA14897@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200221202246.GA14897@hirez.programming.kicks-ass.net> 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 Fri, Feb 21, 2020 at 09:22:46PM +0100, Peter Zijlstra wrote: > On Fri, Feb 21, 2020 at 11:05:36AM -0800, Andy Lutomirski wrote: > > > > - /* > > > - * 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. > > > - */ > > > - ist_enter(regs); > > > + nmi_enter(); > > > > I agree with the change, but some commentary might be nice. Maybe > > copy from here: > > > > https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/idtentry&id=061eaa900b4f63601ab6381ab431fcef8dfd84be > > Fair enough; I'll add something to #DB and #BP for that. do_int3() is now like: @@ -529,19 +497,18 @@ dotraplinkage void do_general_protection } NOKPROBE_SYMBOL(do_general_protection); -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(); RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); #ifdef CONFIG_KGDB_LOW_LEVEL_TRAP if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP, @@ -563,7 +530,7 @@ dotraplinkage void notrace do_int3(struc cond_local_irq_disable(regs); exit: - ist_exit(regs); + nmi_exit(); } NOKPROBE_SYMBOL(do_int3); And I'm going to have to do another (few) patches for do_debug(), because that comment it has it patently false and I remember we had a bunch of crud for that. Let me dig those out.