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=-8.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,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 2E2BBFC6195 for ; Wed, 6 Nov 2019 23:54:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ECCF3206C3 for ; Wed, 6 Nov 2019 23:54:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="UQC0m0r9" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727669AbfKFXyc (ORCPT ); Wed, 6 Nov 2019 18:54:32 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:30988 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727369AbfKFXyc (ORCPT ); Wed, 6 Nov 2019 18:54:32 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1573084471; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=OeBSvkxKgLwEN5Lh3YlOG/EG6vi47zYej441MNR7eJM=; b=UQC0m0r9p+IIhdsv5Ur3HJtVs1YTBiFx8WAyvDgUSthwLf1bNl35o7lrj1Iq4huo9ggixn 07+oWnxpX9uvazg6VDzdpAc9bmZ9G2zUeAmy47rUddV4aCPsDZnVMfHSzOukSb9SMnRU2r a0eDwxeQtL/b8p+Jo7m+1TdgGG8EPnM= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-194-R_j9mkZuOLSRp0VQugwtwA-1; Wed, 06 Nov 2019 18:54:29 -0500 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F00FF1800D63; Wed, 6 Nov 2019 23:54:28 +0000 (UTC) Received: from treble (ovpn-122-162.rdu2.redhat.com [10.10.122.162]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 71EE31A7E3; Wed, 6 Nov 2019 23:54:25 +0000 (UTC) Date: Wed, 6 Nov 2019 17:54:23 -0600 From: Josh Poimboeuf To: Joe Lawrence Cc: linux-kernel@vger.kernel.org, live-patching@vger.kernel.org Subject: Re: [PATCH] x86/stacktrace: update kconfig help text for reliable unwinders Message-ID: <20191106235423.hjamrggd4x3js5hm@treble> References: <20191106224344.8373-1-joe.lawrence@redhat.com> <20191106230553.wnyltmkzwk5dph4l@treble> MIME-Version: 1.0 In-Reply-To: User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-MC-Unique: R_j9mkZuOLSRp0VQugwtwA-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Sender: live-patching-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Wed, Nov 06, 2019 at 06:16:28PM -0500, Joe Lawrence wrote: > On 11/6/19 6:05 PM, Josh Poimboeuf wrote: > > On Wed, Nov 06, 2019 at 05:43:44PM -0500, Joe Lawrence wrote: > > > commit 6415b38bae26 ("x86/stacktrace: Enable HAVE_RELIABLE_STACKTRACE > > > for the ORC unwinder") marked the ORC unwinder as a "reliable" unwind= er. > > > Update the help text to reflect that change: the frame pointer unwind= er > > > is no longer the only one that provides HAVE_RELIABLE_STACKTRACE. > > >=20 > > > Signed-off-by: Joe Lawrence > > > --- > > > arch/x86/Kconfig.debug | 8 ++++---- > > > 1 file changed, 4 insertions(+), 4 deletions(-) > > >=20 > > > diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug > > > index bf9cd83de777..69cdf0558c13 100644 > > > --- a/arch/x86/Kconfig.debug > > > +++ b/arch/x86/Kconfig.debug > > > @@ -316,10 +316,6 @@ config UNWINDER_FRAME_POINTER > > > =09 unwinder, but the kernel text size will grow by ~3% and the ke= rnel's > > > =09 overall performance will degrade by roughly 5-10%. > > > -=09 This option is recommended if you want to use the livepatch > > > -=09 consistency model, as this is currently the only way to get a > > > -=09 reliable stack trace (CONFIG_HAVE_RELIABLE_STACKTRACE). > > > - > > > config UNWINDER_GUESS > > > =09bool "Guess unwinder" > > > =09depends on EXPERT > > > @@ -333,6 +329,10 @@ config UNWINDER_GUESS > > > =09 useful in many cases. Unlike the other unwinders, it has no r= untime > > > =09 overhead. > > > +=09 This option is not recommended if you want to use the livepatch > > > +=09 consistency model, as this unwinder cannot guarantee reliable s= tack > > > +=09 traces. > > > + > >=20 > > I'm not sure whether this last hunk is helpful. At the very least the > > wording of "not recommended" might be confusing because it's not even > > possible to combine UNWINDER_GUESS+HAVE_RELIABLE_STACKTRACE. > >=20 > > arch/x86/Kconfig: select HAVE_RELIABLE_STACKTRACE if X86_= 64 && (UNWINDER_FRAME_POINTER || UNWINDER_ORC) && STACK_VALIDATION > >=20 >=20 > Ah good point. The alternative would be to copy the recommended note to > both UNWINDER_FRAME_POINTER and UNWINDER_ORC, or at least remove the "onl= y" > phrasing. I dunno, nobody has noticed it yet, so maybe the first hunk wo= uld > be good enough. The guess unwinder is listed as an expert option, so the user would have to enable CONFIG_EXPERT to get to it. Then if they do enable it and try to load a livepatch, they'll get a runtime warning along with a patch which never transitions. And like you said, nobody has complained, so I'd say just dropping the 2nd hunk would be fine. --=20 Josh