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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 DDEBEC4360C for ; Thu, 26 Sep 2019 21:43:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AFABF222C2 for ; Thu, 26 Sep 2019 21:43:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726133AbfIZVnE (ORCPT ); Thu, 26 Sep 2019 17:43:04 -0400 Received: from mga07.intel.com ([134.134.136.100]:8270 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725943AbfIZVnE (ORCPT ); Thu, 26 Sep 2019 17:43:04 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga105.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 26 Sep 2019 14:43:03 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,553,1559545200"; d="scan'208";a="192958527" Received: from sjchrist-coffee.jf.intel.com ([10.54.74.41]) by orsmga003.jf.intel.com with ESMTP; 26 Sep 2019 14:43:03 -0700 From: Sean Christopherson To: Paolo Bonzini , =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= Cc: Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Reto Buerki Subject: [PATCH 0/2] KVM: nVMX: Bug fix for consuming stale vmcs02.GUEST_CR3 Date: Thu, 26 Sep 2019 14:43:00 -0700 Message-Id: <20190926214302.21990-1-sean.j.christopherson@intel.com> X-Mailer: git-send-email 2.22.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Reto Buerki reported a failure in a nested VMM when running with HLT interception disabled in L1. When putting L2 into HLT, KVM never actually enters L2 and instead cancels the nested run and pretends that VM-Enter to L2 completed and then exited on HLT (which KVM intercepted). Because KVM never actually runs L2, KVM skips the pending MMU update for L2 and so leaves a stale value in vmcs02.GUEST_CR3. If the next wake event for L2 triggers a nested VM-Exit, KVM will refresh vmcs12->guest_cr3 from vmcs02.GUEST_CR3 and consume the stale value. Fix the issue by unconditionally writing vmcs02.GUEST_CR3 during nested VM-Enter instead of deferring the update to vmx_set_cr3(), and skip the update of GUEST_CR3 in vmx_set_cr3() when running L2. I.e. make the nested code fully responsible for vmcs02.GUEST_CR3. I really wanted to go with a different fix of handling this as a one-off case in the HLT flow (in nested_vmx_run()), and then following that up with a cleanup of VMX's CR3 handling, e.g. to do proper dirty tracking instead of having the nested code do manual VMREADs and VMWRITEs. I even went so far as to hide vcpu->arch.cr3 (put CR3 in vcpu->arch.regs), but things went south when I started working through the dirty tracking logic. Because EPT can be enabled *without* unrestricted guest, enabling EPT doesn't always mean GUEST_CR3 really is the guest CR3 (unlike SVM's NPT). And because the unrestricted guest handling of GUEST_CR3 is dependent on whether the guest has paging enabled, VMX can't even do a clean handoff based on unrestricted guest. In a nutshell, dynamically handling the transitions of GUEST_CR3 ownership in VMX is a nightmare, so fixing this purely within the context of nested VMX turned out to be the cleanest fix. Sean Christopherson (2): KVM: nVMX: Always write vmcs02.GUEST_CR3 during nested VM-Enter KVM: VMX: Skip GUEST_CR3 VMREAD+VMWRITE if the VMCS is up-to-date arch/x86/kvm/vmx/nested.c | 8 ++++++++ arch/x86/kvm/vmx/vmx.c | 15 ++++++++++----- 2 files changed, 18 insertions(+), 5 deletions(-) -- 2.22.0