From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752483AbdJDOEZ (ORCPT ); Wed, 4 Oct 2017 10:04:25 -0400 Received: from mx1.redhat.com ([209.132.183.28]:25112 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752352AbdJDOEX (ORCPT ); Wed, 4 Oct 2017 10:04:23 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 502CF25778 Authentication-Results: ext-mx10.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx10.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=jpoimboe@redhat.com Date: Wed, 4 Oct 2017 09:04:22 -0500 From: Josh Poimboeuf To: Jiri Slaby Cc: mingo@redhat.com, tglx@linutronix.de, hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC 1/1] orc: mark it as reliable Message-ID: <20171004140422.wikfoodyhoas2eae@treble> References: <20171004092315.17129-1-jslaby@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20171004092315.17129-1-jslaby@suse.cz> User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Wed, 04 Oct 2017 14:04:23 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 04, 2017 at 11:23:15AM +0200, Jiri Slaby wrote: > We need a reliable stack unwinder for kernel live patching, but we do > not want to enable frame pointers for performance reasons. So let ORC be > a reliable stack unwinder on x86 as it performs nicely wrt reliability > of traces. > > Signed-off-by: Jiri Slaby > Cc: Josh Poimboeuf > Cc: Thomas Gleixner > Cc: Ingo Molnar > Cc: "H. Peter Anvin" > Cc: x86@kernel.org > --- > > I am sending this as an RFC. Do you still consider ORC to be not-enough > reliable? Off the top of my head, at least the following is missing: - save_stack_trace_reliable() assumes that kernel mode pt_regs on the stack make the stack trace unreliable. This is an FP-specific assumption which no longer applies for ORC. - The ORC unwinder needs to set unwind_state.error if it doesn't reach all the way to the end (user pt_regs). -- Josh