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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C4B40C4332F for ; Tue, 22 Nov 2022 19:13:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234677AbiKVTNl (ORCPT ); Tue, 22 Nov 2022 14:13:41 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42826 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232355AbiKVTNj (ORCPT ); Tue, 22 Nov 2022 14:13:39 -0500 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5833E86A6A; Tue, 22 Nov 2022 11:13:38 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=7fBCU6btn2ZSChSQBKi+ngIee2Y4f+0YlH8/FhLpy98=; b=NXABkzLhZPVQ4q4a4a5Yn8tSo0 MpkbPG9F3xJcLgKUhnksbXsl+A0KKeCEGpacNd6khyo7SXFFybehzs+XaYEDAn5t9pRrYq1TThlAJ pDwp1yGZg9RyfqSwt55C622Igr8IQwnqDHb9p98ufNLcFi3y6Kqwu+WAtZiENmUHQ3A7lklhPEEN/ rvmB3RX1Gv0OfMoMQQ0358KnLBBAAlKaKjAC3j5NUgiRAmkzp73rbJ1mf3u+dwXlW5gc0JeXwHAZj in2Gi8wKxOgqX5jOWarRVzxnkkoz4L/EKQ4t51BQwZg3wv+PFqlaGVdnvYbyzPN9CvbyoQKaR25E5 kzt6K8Wg==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1oxYhv-003Ys2-IN; Tue, 22 Nov 2022 19:13:23 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id C7653300202; Tue, 22 Nov 2022 20:13:21 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id AC26120B64111; Tue, 22 Nov 2022 20:13:21 +0100 (CET) Date: Tue, 22 Nov 2022 20:13:21 +0100 From: Peter Zijlstra To: Dave Hansen Cc: Kai Huang , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org, seanjc@google.com, pbonzini@redhat.com, dan.j.williams@intel.com, rafael.j.wysocki@intel.com, kirill.shutemov@linux.intel.com, ying.huang@intel.com, reinette.chatre@intel.com, len.brown@intel.com, tony.luck@intel.com, ak@linux.intel.com, isaku.yamahata@intel.com, chao.gao@intel.com, sathyanarayanan.kuppuswamy@linux.intel.com, bagasdotme@gmail.com, sagis@google.com, imammedo@redhat.com Subject: Re: [PATCH v7 06/20] x86/virt/tdx: Shut down TDX module in case of error Message-ID: References: <48505089b645019a734d85c2c29f3c8ae2dbd6bd.1668988357.git.kai.huang@intel.com> <52b2be9b-defd-63ce-4cb2-96cd624a95a6@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <52b2be9b-defd-63ce-4cb2-96cd624a95a6@intel.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, Nov 22, 2022 at 07:14:14AM -0800, Dave Hansen wrote: > On 11/22/22 01:13, Peter Zijlstra wrote: > > On Mon, Nov 21, 2022 at 01:26:28PM +1300, Kai Huang wrote: > >> +/* > >> + * Call the SEAMCALL on all online CPUs concurrently. Caller to check > >> + * @sc->err to determine whether any SEAMCALL failed on any cpu. > >> + */ > >> +static void seamcall_on_each_cpu(struct seamcall_ctx *sc) > >> +{ > >> + on_each_cpu(seamcall_smp_call_function, sc, true); > >> +} > > > > Suppose the user has NOHZ_FULL configured, and is already running > > userspace that will terminate on interrupt (this is desired feature for > > NOHZ_FULL), guess how happy they'll be if someone, on another parition, > > manages to tickle this TDX gunk? > > Yeah, they'll be none too happy. > > But, what do we do? Not intialize TDX on busy NOHZ_FULL cpus and hard-limit the cpumask of all TDX using tasks. > There are technical solutions like detecting if NOHZ_FULL is in play and > refusing to initialize TDX. There are also non-technical solutions like > telling folks in the documentation that they better modprobe kvm early > if they want to do TDX, or their NOHZ_FULL apps will pay. Surely modprobe kvm isn't the point where TDX gets loaded? Because that's on boot for everybody due to all the auto-probing nonsense. I was expecting TDX to not get initialized until the first TDX using KVM instance is created. Am I wrong? > We could also force the TDX module to be loaded early in boot before > NOHZ_FULL is in play, but that would waste memory on TDX metadata even > if TDX is never used. I'm thikning it makes sense to have a tdx={off,on-demand,force} toggle anyway. > How do NOHZ_FULL folks deal with late microcode updates, for example? > Those are roughly equally disruptive to all CPUs. I imagine they don't do that -- in fact I would recommend we make the whole late loading thing mutually exclusive with nohz_full; can't have both.