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=-9.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,HK_RANDOM_FROM,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 4F8E2C4743F for ; Mon, 7 Jun 2021 09:23:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3417560232 for ; Mon, 7 Jun 2021 09:23:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230389AbhFGJZg (ORCPT ); Mon, 7 Jun 2021 05:25:36 -0400 Received: from mga09.intel.com ([134.134.136.24]:8583 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230200AbhFGJZd (ORCPT ); Mon, 7 Jun 2021 05:25:33 -0400 IronPort-SDR: mycNHMkTkL3f/NEEZ+18acCX3/ICXUwHWRaOw7MYchcsEnfGw4vxFw1+QRgf7KDRPtCx8fua7u Z8F/B7BZi7hw== X-IronPort-AV: E=McAfee;i="6200,9189,10007"; a="204559400" X-IronPort-AV: E=Sophos;i="5.83,254,1616482800"; d="scan'208";a="204559400" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 Jun 2021 02:23:41 -0700 IronPort-SDR: mn3a0b9mDoaeFl4s5SQNEFzCDKBns5YRj+j+JGoMv4y+RAOe6sJxxB1vD+023HCJsxRIwRkDE+ M3eiwjvVk06Q== X-IronPort-AV: E=Sophos;i="5.83,254,1616482800"; d="scan'208";a="447423811" Received: from yujie-nuc.sh.intel.com (HELO [10.239.13.110]) ([10.239.13.110]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 Jun 2021 02:23:37 -0700 Subject: Re: [PATCH v2] KVM: VMX: Enable Notify VM exit To: Vitaly Kuznetsov , Tao Xu Cc: x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, seanjc@google.com, wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com References: <20210525051204.1480610-1-tao3.xu@intel.com> <871r9k36ds.fsf@vitty.brq.redhat.com> <660ceed2-7569-6ce6-627a-9a4e860b8aa9@intel.com> <87fsxz12e9.fsf@vitty.brq.redhat.com> From: Xiaoyao Li Message-ID: <75336195-8360-656e-c6a2-dda9ed152029@intel.com> Date: Mon, 7 Jun 2021 17:23:35 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <87fsxz12e9.fsf@vitty.brq.redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/3/2021 9:52 PM, Vitaly Kuznetsov wrote: > Xiaoyao Li writes: > >> On 6/2/2021 6:31 PM, Vitaly Kuznetsov wrote: >>> Tao Xu writes: >>> >>>> There are some cases that malicious virtual machines can cause CPU stuck >>>> (event windows don't open up), e.g., infinite loop in microcode when >>>> nested #AC (CVE-2015-5307). No event window obviously means no events, >>>> e.g. NMIs, SMIs, and IRQs will all be blocked, may cause the related >>>> hardware CPU can't be used by host or other VM. >>>> >>>> To resolve those cases, it can enable a notify VM exit if no event >>>> window occur in VMX non-root mode for a specified amount of time >>>> (notify window). Since CPU is first observed the risk of not causing >>>> forward progress, after notify window time in a units of crystal clock, >>>> Notify VM exit will happen. Notify VM exit can happen incident to delivery >>>> of a vectored event. >>>> >>>> Expose a module param for configuring notify window, which is in unit of >>>> crystal clock cycle. >>>> - A negative value (e.g. -1) is to disable this feature. >>>> - Make the default as 0. It is safe because an internal threshold is added >>>> to notify window to ensure all the normal instructions being coverd. >>>> - User can set it to a large value when they want to give more cycles to >>>> wait for some reasons, e.g., silicon wrongly kill some normal instruction >>>> due to internal threshold is too small. >>>> >>>> Notify VM exit is defined in latest Intel Architecture Instruction Set >>>> Extensions Programming Reference, chapter 9.2. >>>> >>>> Co-developed-by: Xiaoyao Li >>>> Signed-off-by: Xiaoyao Li >>>> Signed-off-by: Tao Xu >>>> --- >>>> >>>> Changelog: >>>> v2: >>>> Default set notify window to 0, less than 0 to disable. >>>> Add more description in commit message. >>> >>> Sorry if this was already discussed, but in case of nested >>> virtualization and when L1 also enables >>> SECONDARY_EXEC_NOTIFY_VM_EXITING, shouldn't we just reflect NOTIFY exits >>> during L2 execution to L1 instead of crashing the whole L1? >>> >> >> yes. If we expose it to nested, it should reflect the Notify VM exit to >> L1 when L1 enables it. >> >> But regarding nested, there are more things need to be discussed. e.g., >> 1) It has dependence between L0 and L1, for security consideration. When >> L0 enables it, it shouldn't be turned off during L2 VM is running. >> a. Don't expose to L1 but enable for L1 when L2 VM is running. >> b. expose it to L1 and force it enabled. > > Could you please elaborate on the 'security' concern? I mean the case that if we expose this feature to L1 VMM, L1 VMM cannot en/dis-able this feature on its own purpose when L0 turns it on. i.e., vmcs02.settings has to be (L0's | L1's) otherwise L1 guest can escape by creating an nested guest and disabling it. > My understanding > that during L2 execution: > If L0 enables the feature and L1 doesn't, vmexit goes to L0. > If L1 enables the feature and L0 doesn't, vmexit goes to L1. > If both L0 and L1 enable the feature, vmexit can probably (I didn't put > enough though in it I'm afraid) go to the one which has smaller window. It sounds reasonable. >> >> 2) When expose it to L1, vmcs02.notify_window needs to be >> min(L0.notify_window, L1.nofity_window) >> >> We don't deal with nested to make this Patch simple. > > Sure, I just wanted to check with you what's the future plan and if the > behavior you introduce is desireable in nested case. >