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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, 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 C76DFC18E5A for ; Mon, 9 Mar 2020 09:09:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AAFB320848 for ; Mon, 9 Mar 2020 09:09:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726633AbgCIJJF (ORCPT ); Mon, 9 Mar 2020 05:09:05 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:58275 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726383AbgCIJJF (ORCPT ); Mon, 9 Mar 2020 05:09:05 -0400 Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jBEPF-0004Dh-IA; Mon, 09 Mar 2020 10:09:01 +0100 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id A737310408A; Mon, 9 Mar 2020 10:09:00 +0100 (CET) From: Thomas Gleixner To: Paolo Bonzini , Andy Lutomirski Cc: LKML , X86 ML , kvm list , stable Subject: Re: [PATCH v2] x86/kvm: Disable KVM_ASYNC_PF_SEND_ALWAYS In-Reply-To: <37440ade-1657-648b-bf72-2b8ca4ac21ce@redhat.com> References: <87ftek9ngq.fsf@nanos.tec.linutronix.de> <87a74s9ehb.fsf@nanos.tec.linutronix.de> <87wo7v8g4j.fsf@nanos.tec.linutronix.de> <877dzu8178.fsf@nanos.tec.linutronix.de> <37440ade-1657-648b-bf72-2b8ca4ac21ce@redhat.com> Date: Mon, 09 Mar 2020 10:09:00 +0100 Message-ID: <871rq199oz.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Paolo Bonzini writes: > On 09/03/20 07:57, Thomas Gleixner wrote: >> Thomas Gleixner writes: >> >> guest side: >> >> nmi()/mce() ... >> >> stash_crs(); >> >> + stash_and_clear_apf_reason(); >> >> .... >> >> + restore_apf_reason(); >> >> restore_cr2(); >> >> Too obvious, isn't it? > > Yes, this works but Andy was not happy about adding more > save-and-restore to NMIs. If you do not want to do that, I'm okay with > disabling async page fault support for now. I'm fine with doing that save/restore dance, but I have no strong opinion either. > Storing the page fault reason in memory was not a good idea. Better > options would be to co-opt the page fault error code (e.g. store the > reason in bits 31:16, mark bits 15:0 with the invalid error code > RSVD=1/P=0), or to use the virtualization exception area. Memory store is not the problem. The real problem is hijacking #PF. If you'd have just used a separate VECTOR_ASYNC_PF then none of these problems would exist at all. Thanks, tglx