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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 AFFE5C43461 for ; Mon, 14 Sep 2020 16:55:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6B1B0206E6 for ; Mon, 14 Sep 2020 16:55:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726318AbgINQzr (ORCPT ); Mon, 14 Sep 2020 12:55:47 -0400 Received: from mga06.intel.com ([134.134.136.31]:22800 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726028AbgINQta (ORCPT ); Mon, 14 Sep 2020 12:49:30 -0400 IronPort-SDR: k9nx0JRIppzFqoh8vYH26k2mTMxI29e/dnimL5GwI1JZ5rLjcg7vGBWhwZfizLgqSOHi83jzfh XJMqAD8eNgcw== X-IronPort-AV: E=McAfee;i="6000,8403,9744"; a="220665952" X-IronPort-AV: E=Sophos;i="5.76,426,1592895600"; d="scan'208";a="220665952" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Sep 2020 09:49:27 -0700 IronPort-SDR: Pm7ODHiCR14OAqKMe6ftIHPePn/ldSOJmEGdRKEsdBg/QTPXWwHDj+P9U9nih+5WtzffrcquYz cz48HB1H/SOg== X-IronPort-AV: E=Sophos;i="5.76,426,1592895600"; d="scan'208";a="507207696" Received: from sjchrist-ice.jf.intel.com (HELO sjchrist-ice) ([10.54.31.34]) by fmsmga005-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Sep 2020 09:49:26 -0700 Date: Mon, 14 Sep 2020 09:49:24 -0700 From: Sean Christopherson To: Alex Williamson Cc: Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Xiong Zhang , Wayne Boyer , Zhenyu Wang , Jun Nakajima , Weijiang Yang Subject: Re: [PATCH] KVM: x86/mmu: Add capability to zap only sptes for the affected memslot Message-ID: <20200914164923.GH6855@sjchrist-ice> References: <51637a13-f23b-8b76-c93a-76346b4cc982@redhat.com> <20200709211253.GW24919@linux.intel.com> <49c7907a-3ab4-b5db-ccb4-190b990c8be3@redhat.com> <20200710042922.GA24919@linux.intel.com> <20200713122226.28188f93@x1.home> <20200713190649.GE29725@linux.intel.com> <20200721030319.GD20375@linux.intel.com> <20200721100036.464d4440@w520.home> <20200723155711.GD21891@linux.intel.com> <20200723123544.6268b465@w520.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200723123544.6268b465@w520.home> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, Jul 23, 2020 at 12:35:44PM -0600, Alex Williamson wrote: > On Thu, 23 Jul 2020 08:57:11 -0700 > Sean Christopherson wrote: > > > On Tue, Jul 21, 2020 at 10:00:36AM -0600, Alex Williamson wrote: > > > On Mon, 20 Jul 2020 20:03:19 -0700 > > > Sean Christopherson wrote: > > > > > > > +Weijiang > > > > > > > > On Mon, Jul 13, 2020 at 12:06:50PM -0700, Sean Christopherson wrote: > > > > > The only ideas I have going forward are to: > > > > > > > > > > a) Reproduce the bug outside of your environment and find a resource that > > > > > can go through the painful bisection. > > > > > > > > We're trying to reproduce the original issue in the hopes of biesecting, but > > > > have not yet discovered the secret sauce. A few questions: > > > > > > > > - Are there any known hardware requirements, e.g. specific flavor of GPU? > > > > > > I'm using an old GeForce GT635, I don't think there's anything special > > > about this card. > > > > Would you be able to provide your QEMU command line? Or at least any > > potentially relevant bits? Still no luck reproducing this on our end. *sigh* The "good" news is that we were able to reproduce and bisect the "fix". That bad news is that the "fix" is the fracturing of large pages for the iTLB multi-hit bug, added by commit b8e8c8303ff2 ("kvm: mmu: ITLB_MULTIHIT mitigation"). The GPU pass-through failures can be reproduced by loading KVM with kvm.nx_huge_pages=0. So, we have another data point, but still no clear explanation of exactly what is broken.