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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 621B5C10DCE for ; Sat, 7 Mar 2020 02:26:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 38E96206D7 for ; Sat, 7 Mar 2020 02:26:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1583548009; bh=WarD3A6TIXCvkh+npVTJxWlJCe2Sm4j29KWN/2pPhhs=; h=From:To:Cc:Subject:Date:List-ID:From; b=mMQZcuPccMmESEBQI5RkevjNnKMhpNS96rDLtWtk2E0oq/agVQSuIgp4NynIjQcos cpWobWyFC2AYRSqPrj/TADRxQbmLKW6IgMPipD6QvgD+csQ1tQJI4JLWjnJyqwxy9v wKc5BornnCWtHt+IE59bq6ahr9AEaghSAEH9RICs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726824AbgCGC0q (ORCPT ); Fri, 6 Mar 2020 21:26:46 -0500 Received: from mail.kernel.org ([198.145.29.99]:57506 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726231AbgCGC0q (ORCPT ); Fri, 6 Mar 2020 21:26:46 -0500 Received: from localhost (c-67-180-165-146.hsd1.ca.comcast.net [67.180.165.146]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9E16F206D7; Sat, 7 Mar 2020 02:26:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1583548005; bh=WarD3A6TIXCvkh+npVTJxWlJCe2Sm4j29KWN/2pPhhs=; h=From:To:Cc:Subject:Date:From; b=DiSG3DrXPw/2Hmyg25twSuLwoqauursyOSyV1GXzwE4VozYSRkfcKMFCBZmtB+DuZ 0adtWc+A1yF2nvqvsJCzfaescMRw5SEURNmEi3DotQWHn/bSF4sq9h4dfrwMSG22Sc IcN6/3NDPR/obHD63od1YtxF0qTzOkv8TT/4xlvQ= From: Andy Lutomirski To: LKML , x86@kernel.org, kvm list , Paolo Bonzini Cc: Andy Lutomirski , stable@vger.kernel.org Subject: [PATCH v2] x86/kvm: Disable KVM_ASYNC_PF_SEND_ALWAYS Date: Fri, 6 Mar 2020 18:26:42 -0800 Message-Id: X-Mailer: git-send-email 2.24.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The ABI is broken and we cannot support it properly. Turn it off. If this causes a meaningful performance regression for someone, KVM can introduce an improved ABI that is supportable. Cc: stable@vger.kernel.org Signed-off-by: Andy Lutomirski --- arch/x86/kernel/kvm.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 93ab0cbd304e..e6f2aefa298b 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -318,11 +318,26 @@ static void kvm_guest_cpu_init(void) pa = slow_virt_to_phys(this_cpu_ptr(&apf_reason)); -#ifdef CONFIG_PREEMPTION - pa |= KVM_ASYNC_PF_SEND_ALWAYS; -#endif pa |= KVM_ASYNC_PF_ENABLED; + /* + * We do not set KVM_ASYNC_PF_SEND_ALWAYS. With the current + * KVM paravirt ABI, the following scenario is possible: + * + * #PF: async page fault (KVM_PV_REASON_PAGE_NOT_PRESENT) + * NMI before CR2 or KVM_PF_REASON_PAGE_NOT_PRESENT + * NMI accesses user memory, e.g. due to perf + * #PF: normal page fault + * #PF reads CR2 and apf_reason -- apf_reason should be 0 + * + * outer #PF reads CR2 and apf_reason -- apf_reason should be + * KVM_PV_REASON_PAGE_NOT_PRESENT + * + * There is no possible way that both reads of CR2 and + * apf_reason get the correct values. Fixing this would + * require paravirt ABI changes. + */ + if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF_VMEXIT)) pa |= KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT; -- 2.24.1