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 B2D1EC43334 for ; Fri, 3 Jun 2022 17:56:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345875AbiFCR4o (ORCPT ); Fri, 3 Jun 2022 13:56:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58130 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346076AbiFCRzj (ORCPT ); Fri, 3 Jun 2022 13:55:39 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 37209562F3; Fri, 3 Jun 2022 10:53:38 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id C4F1C61244; Fri, 3 Jun 2022 17:53:37 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B6B7EC385A9; Fri, 3 Jun 2022 17:53:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1654278817; bh=CHmgGFpsuDekL9gLWFmcxOCEDhBVsTKgnNsfGL5LnfI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TukBTrZXhnSFffHwoWuD3m72sxyOdz8ODuVpOJkA90LW8dSqTK0EKN4Ygvnk7VQA8 CNJXR5mJHDp8d71B3k1x7e2KDeX6Tk1kfEL7mote41wHP+kZgzMT37cYQoh5DPtx4F WMMGxOjWmXL7fYCa855b7u6nRWAwOtlczXlmEhk8= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Chenyi Qiang , Sean Christopherson , Paolo Bonzini Subject: [PATCH 5.17 37/75] KVM: x86: Drop WARNs that assert a triple fault never "escapes" from L2 Date: Fri, 3 Jun 2022 19:43:21 +0200 Message-Id: <20220603173822.797923186@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220603173821.749019262@linuxfoundation.org> References: <20220603173821.749019262@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Sean Christopherson commit 45846661d10422ce9e22da21f8277540b29eca22 upstream. Remove WARNs that sanity check that KVM never lets a triple fault for L2 escape and incorrectly end up in L1. In normal operation, the sanity check is perfectly valid, but it incorrectly assumes that it's impossible for userspace to induce KVM_REQ_TRIPLE_FAULT without bouncing through KVM_RUN (which guarantees kvm_check_nested_state() will see and handle the triple fault). The WARN can currently be triggered if userspace injects a machine check while L2 is active and CR4.MCE=0. And a future fix to allow save/restore of KVM_REQ_TRIPLE_FAULT, e.g. so that a synthesized triple fault isn't lost on migration, will make it trivially easy for userspace to trigger the WARN. Clearing KVM_REQ_TRIPLE_FAULT when forcibly leaving guest mode is tempting, but wrong, especially if/when the request is saved/restored, e.g. if userspace restores events (including a triple fault) and then restores nested state (which may forcibly leave guest mode). Ignoring the fact that KVM doesn't currently provide the necessary APIs, it's userspace's responsibility to manage pending events during save/restore. ------------[ cut here ]------------ WARNING: CPU: 7 PID: 1399 at arch/x86/kvm/vmx/nested.c:4522 nested_vmx_vmexit+0x7fe/0xd90 [kvm_intel] Modules linked in: kvm_intel kvm irqbypass CPU: 7 PID: 1399 Comm: state_test Not tainted 5.17.0-rc3+ #808 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:nested_vmx_vmexit+0x7fe/0xd90 [kvm_intel] Call Trace: vmx_leave_nested+0x30/0x40 [kvm_intel] vmx_set_nested_state+0xca/0x3e0 [kvm_intel] kvm_arch_vcpu_ioctl+0xf49/0x13e0 [kvm] kvm_vcpu_ioctl+0x4b9/0x660 [kvm] __x64_sys_ioctl+0x83/0xb0 do_syscall_64+0x3b/0xc0 entry_SYSCALL_64_after_hwframe+0x44/0xae ---[ end trace 0000000000000000 ]--- Fixes: cb6a32c2b877 ("KVM: x86: Handle triple fault in L2 without killing L1") Cc: stable@vger.kernel.org Cc: Chenyi Qiang Signed-off-by: Sean Christopherson Message-Id: <20220407002315.78092-2-seanjc@google.com> Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/svm/nested.c | 3 --- arch/x86/kvm/vmx/nested.c | 3 --- 2 files changed, 6 deletions(-) --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -790,9 +790,6 @@ int nested_svm_vmexit(struct vcpu_svm *s struct kvm_host_map map; int rc; - /* Triple faults in L2 should never escape. */ - WARN_ON_ONCE(kvm_check_request(KVM_REQ_TRIPLE_FAULT, vcpu)); - rc = kvm_vcpu_map(vcpu, gpa_to_gfn(svm->nested.vmcb12_gpa), &map); if (rc) { if (rc == -EINVAL) --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -4518,9 +4518,6 @@ void nested_vmx_vmexit(struct kvm_vcpu * /* trying to cancel vmlaunch/vmresume is a bug */ WARN_ON_ONCE(vmx->nested.nested_run_pending); - /* Similarly, triple faults in L2 should never escape. */ - WARN_ON_ONCE(kvm_check_request(KVM_REQ_TRIPLE_FAULT, vcpu)); - if (kvm_check_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu)) { /* * KVM_REQ_GET_NESTED_STATE_PAGES is also used to map