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 0766CFC6194 for ; Wed, 6 Nov 2019 23:16:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C136E20656 for ; Wed, 6 Nov 2019 23:16:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="F8Pomh5a" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727177AbfKFXQd (ORCPT ); Wed, 6 Nov 2019 18:16:33 -0500 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:30172 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727080AbfKFXQd (ORCPT ); Wed, 6 Nov 2019 18:16:33 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1573082192; 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=5tuNiF4QO0bwSBu7oymDSjgkRdbR3Qfk0s5KVbUvZoM=; b=F8Pomh5axd5LTT4cPgdXgKnhBVDiXSXiSulkH142vJi06KKbFF3nckryFF+az8b/1KQwdt wr1FIwJHrvOom1smqKS8YT/sSqJM0Ko0E/fvMt+v4bQWjNDxGmETCJ+kuoNGnf3qX3yVJF XxbI10qiPNM2nHK+PeWmlSFVjr7yAyc= 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-321-ObXpTYzpMbyrccMiwEOx3g-1; Wed, 06 Nov 2019 18:16:30 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B4ADA1800D53; Wed, 6 Nov 2019 23:16:29 +0000 (UTC) Received: from [10.18.17.119] (dhcp-17-119.bos.redhat.com [10.18.17.119]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5BB1860870; Wed, 6 Nov 2019 23:16:29 +0000 (UTC) Subject: Re: [PATCH] x86/stacktrace: update kconfig help text for reliable unwinders To: Josh Poimboeuf Cc: linux-kernel@vger.kernel.org, live-patching@vger.kernel.org References: <20191106224344.8373-1-joe.lawrence@redhat.com> <20191106230553.wnyltmkzwk5dph4l@treble> From: Joe Lawrence Message-ID: Date: Wed, 6 Nov 2019 18:16:28 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20191106230553.wnyltmkzwk5dph4l@treble> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-MC-Unique: ObXpTYzpMbyrccMiwEOx3g-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable Sender: live-patching-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org Archived-At: List-Archive: List-Post: 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" unwinder. >> Update the help text to reflect that change: the frame pointer unwinder >> is no longer the only one that provides HAVE_RELIABLE_STACKTRACE. >> >> Signed-off-by: Joe Lawrence >> --- >> arch/x86/Kconfig.debug | 8 ++++---- >> 1 file changed, 4 insertions(+), 4 deletions(-) >> >> 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 kerne= l's >> =09 overall performance will degrade by roughly 5-10%. >> =20 >> -=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 runt= ime >> =09 overhead. >> =20 >> +=09 This option is not recommended if you want to use the livepatch >> +=09 consistency model, as this unwinder cannot guarantee reliable stac= k >> +=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 Ah good point. The alternative would be to copy the recommended note to=20 both UNWINDER_FRAME_POINTER and UNWINDER_ORC, or at least remove the=20 "only" phrasing. I dunno, nobody has noticed it yet, so maybe the first=20 hunk would be good enough. -- Joe