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 2E5C6CCA489 for ; Fri, 3 Jun 2022 18:16:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348142AbiFCSQX (ORCPT ); Fri, 3 Jun 2022 14:16:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40290 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346102AbiFCSBk (ORCPT ); Fri, 3 Jun 2022 14:01:40 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D95304A906; Fri, 3 Jun 2022 10:57:41 -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 ams.source.kernel.org (Postfix) with ESMTPS id E7F38B8241E; Fri, 3 Jun 2022 17:56:59 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3F6B7C385A9; Fri, 3 Jun 2022 17:56:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1654279018; bh=visI1TTHwmCqbAwL6UAvfvNG1u2FwYk4D+zDUFCK6Sc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=EEH0YNuEdLVBssrhhbFCr5rqdcryulFM1vz0YfY4NkeF9JlReHJ8rIsp3Z5wlwh6M TTu7PSxVRQBT0TdWVUDMe4UJssQ8qjJ9nSdOcmQlY5etXmexusyQVgGvOnoScWoYmj ltKR5YbQwwj09I14+mjfuuDauhgZZgZ2XbbhD2Pw= 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 5.18 26/67] KVM: x86: Drop WARNs that assert a triple fault never "escapes" from L2 Date: Fri, 3 Jun 2022 19:43:27 +0200 Message-Id: <20220603173821.478797713@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220603173820.731531504@linuxfoundation.org> References: <20220603173820.731531504@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: linux-kernel@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 @@ -819,9 +819,6 @@ 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