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=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 9A3D7C4321A for ; Tue, 11 Jun 2019 16:11:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 715D22145D for ; Tue, 11 Jun 2019 16:11:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391909AbfFKQLR convert rfc822-to-8bit (ORCPT ); Tue, 11 Jun 2019 12:11:17 -0400 Received: from mail.kernel.org ([198.145.29.99]:45348 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388744AbfFKQLQ (ORCPT ); Tue, 11 Jun 2019 12:11:16 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 3FE1A21726; Tue, 11 Jun 2019 16:11:14 +0000 (UTC) Date: Tue, 11 Jun 2019 12:11:12 -0400 From: Steven Rostedt To: Andy Lutomirski Cc: Peter Zijlstra , Masami Hiramatsu , x86@kernel.org, linux-kernel@vger.kernel.org, Ard Biesheuvel , Andy Lutomirski , Ingo Molnar , Thomas Gleixner , Linus Torvalds , Jason Baron , Jiri Kosina , David Laight , Borislav Petkov , Julia Cartwright , Jessica Yu , "H. Peter Anvin" , Nadav Amit , Rasmus Villemoes , Edward Cree , Daniel Bristot de Oliveira Subject: Re: [PATCH 08/15] x86/alternatives: Teach text_poke_bp() to emulate instructions Message-ID: <20190611121112.1c96aec3@gandalf.local.home> In-Reply-To: <435093E5-6FE3-4DAA-9ABE-EB9D372F8CF8@amacapital.net> References: <20190605130753.327195108@infradead.org> <20190605131945.005681046@infradead.org> <20190608004708.7646b287151cf613838ce05f@kernel.org> <20190607173427.GK3436@hirez.programming.kicks-ass.net> <3DA961AB-950B-4886-9656-C0D268D521F1@amacapital.net> <20190611080307.GN3436@hirez.programming.kicks-ass.net> <435093E5-6FE3-4DAA-9ABE-EB9D372F8CF8@amacapital.net> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 11 Jun 2019 08:54:23 -0700 Andy Lutomirski wrote: > How does that help? If RIP == x+2 and you want to put a 5-byte jump > at address x, no amount of 0xcc is going to change the fact that RIP > is in the middle of the jump. > > Live patching can handle this by detecting this condition on each > CPU, but performance won’t be great. Maybe some synchronize_sched > trickery could help. We have synchronize_rcu_tasks() which return after all tasks have either entered user space or did a voluntary schedule (was not preempted). Or have not run (still in a sleeping state). That way we guarantee that all tasks are no longer on any trampoline or code paths that do not call schedule. I use this to free dynamically allocated trampolines used by ftrace. And kprobes uses this too for its own trampolines. -- Steve