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=-4.0 required=3.0 tests=BAYES_00,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 3B551C433DB for ; Mon, 25 Jan 2021 20:58:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 032AA2256F for ; Mon, 25 Jan 2021 20:58:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732333AbhAYU5j (ORCPT ); Mon, 25 Jan 2021 15:57:39 -0500 Received: from mail.kernel.org ([198.145.29.99]:53012 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732008AbhAYU5L (ORCPT ); Mon, 25 Jan 2021 15:57:11 -0500 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (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 1882522513; Mon, 25 Jan 2021 20:56:30 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=wait-a-minute.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94) (envelope-from ) id 1l48uR-009xpQ-UP; Mon, 25 Jan 2021 20:56:28 +0000 Date: Mon, 25 Jan 2021 20:56:27 +0000 Message-ID: <87pn1ska6c.wl-maz@kernel.org> From: Marc Zyngier To: Oliver Upton , Sasha Levin Cc: dbrazdil@google.com, hns@goldelico.com, linux-kernel@vger.kernel.org Subject: Re: [BUG]: KVM: arm64: Fix symbol dependency in __hyp_call_panic_nvhe In-Reply-To: <20210125200756.1249239-1-oupton@google.com> References: <20200914133626.hlsvu5kces3wsirr@google.com> <20210125200756.1249239-1-oupton@google.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: oupton@google.com, sashal@kernel.org, dbrazdil@google.com, hns@goldelico.com, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi all, On Mon, 25 Jan 2021 20:07:56 +0000, Oliver Upton wrote: > > > That means we have two options: > > (a) define __hyp_panic_string in a different .c file in all pre-5.9 branches, or > > (b) revert the backported patch. > > > > The patch was needed in 5.9 and should stay there. It wasn't needed in earlier > > versions because the symbol was being kept alive by another user. It did "fix" > > the inline asm semantics, but the problem was never triggered in pre-5.9. > > > > Sasha, with this and the GCC bug in mind, would you agree that (b) is the > > better course of action? > > Sasha, > > Any chance we can get this patch reverted as David has suggested? It > was backported to 5.4 LTS in commit 653ae33b030b ("KVM: arm64: Fix > symbol dependency in __hyp_call_panic_nvhe") and is causing build > issues with a 4.9.4 vintage of GCC. Absolutely. This issue has been lingering for some time now, and needs addressing. I'm definitely in favour of reverting this patch, although there are two possible alternatives: - Cherry-pick 9fd339a45be5 ("arm64: Work around broken GCC 4.9 handling of "S" constraint"), which works around this particular GCC bug - Cherry-pick dca5244d2f5b ("compiler.h: Raise minimum version of GCC to 5.1 for arm64"), which forbids GCC 4.9 as it has been demonstrated to mis-compile the kernel (and this patch is targeting stable anyway) Thanks, M. -- Without deviation from the norm, progress is not possible.