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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 93F69C54E8D for ; Mon, 11 May 2020 17:10:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7CAC820714 for ; Mon, 11 May 2020 17:10:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730774AbgEKRKI (ORCPT ); Mon, 11 May 2020 13:10:08 -0400 Received: from mga09.intel.com ([134.134.136.24]:27175 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729731AbgEKRKI (ORCPT ); Mon, 11 May 2020 13:10:08 -0400 IronPort-SDR: UOrVq0WhKJ02UtjCLWrCTehVVmL3frWjKlyyvGmsolzIBUYwQvH0ii8rPUcfvyr1ltZUbjpbQa ZVGd7s5gwAog== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 May 2020 10:10:07 -0700 IronPort-SDR: JGH+TqWPyefkPNqmFTqFqaFL1MHmBZSL6zXfqxqEeF75jsqC+y0DfhBHPCfW38XjrnlZPv6QN8 NkD9OOphzsrA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,380,1583222400"; d="scan'208";a="279845546" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.152]) by orsmga002.jf.intel.com with ESMTP; 11 May 2020 10:10:07 -0700 Date: Mon, 11 May 2020 10:10:07 -0700 From: Sean Christopherson To: Oliver Upton Cc: Peter Xu , Paolo Bonzini , kvm list , Linux Kernel Mailing List , Tony Cook , zoran.davidovac@gmail.com, euloanty@live.com Subject: Re: [PATCH] KVM: Fix a warning in __kvm_gfn_to_hva_cache_init() Message-ID: <20200511171007.GE24052@linux.intel.com> References: <20200504190526.84456-1-peterx@redhat.com> <20200505013929.GA17225@linux.intel.com> <20200505141245.GH6299@xz-x1> <20200511160537.GC24052@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, May 11, 2020 at 10:04:29AM -0700, Oliver Upton wrote: > On Mon, May 11, 2020 at 9:05 AM Sean Christopherson > wrote: > > > > +cc a few other people that have reported this at one time or another. > > > > On Tue, May 05, 2020 at 10:12:45AM -0400, Peter Xu wrote: > > > On Mon, May 04, 2020 at 06:39:29PM -0700, Sean Christopherson wrote: > > > > On Mon, May 04, 2020 at 03:05:26PM -0400, Peter Xu wrote: > > > > > GCC 10.0.1 gives me this warning when building KVM: > > > > > > > > > > warning: ‘nr_pages_avail’ may be used uninitialized in this function [-Wmaybe-uninitialized] > > > > > 2442 | for ( ; start_gfn <= end_gfn; start_gfn += nr_pages_avail) { > > > > > > > > > > It should not happen, but silent it. > > > > > > > > Heh, third times a charm? This has been reported and proposed twice > > > > before[1][2]. Are you using any custom compiler flags? E.g. -O3 is known > > > > to cause false positives with -Wmaybe-uninitialized. > > > > > > No, what I did was only upgrading to Fedora 32 (which will auto-upgrade GCC), > > > so it should be using the default params of whatever provided. > > > > > > > > > > > If we do end up killing this warning, I'd still prefer to use > > > > uninitialized_var() over zero-initializing the variable. > > > > > > > > [1] https://lkml.kernel.org/r/20200218184756.242904-1-oupton@google.com > > > > [2] https://bugzilla.kernel.org/show_bug.cgi?id=207173 > > > > > > OK, I didn't know this is a known problem and discussions going on. But I > > > guess it would be good to address this sooner because it could become a common > > > warning very soon after people upgrades gcc. > > > > Ya, others are hitting this as well. It's especially painful with the > > existence of KVM_WERROR. > > > > Paolo, any preference on how to resolve this? It would appear GCC 10 got > > "smarter". > > Seems that doing absolutely nothing was the fix here :) See: > > 78a5255ffb6a ("Stop the ad-hoc games with -Wno-maybe-initialized") Ah, perfect! Thanks Oliver.