Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752643AbdGLNuz (ORCPT ); Wed, 12 Jul 2017 09:50:55 -0400 Received: from mail-oi0-f66.google.com ([209.85.218.66]:35935 "EHLO mail-oi0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751062AbdGLNux (ORCPT ); Wed, 12 Jul 2017 09:50:53 -0400 MIME-Version: 1.0 In-Reply-To: <44ce44eb-85c3-4fdb-b2ee-602ac2f9e14f@redhat.com> References: <1499757180-20439-1-git-send-email-wanpeng.li@hotmail.com> <20170711155458.GB28875@potion> <44ce44eb-85c3-4fdb-b2ee-602ac2f9e14f@redhat.com> From: Wanpeng Li Date: Wed, 12 Jul 2017 21:50:52 +0800 Message-ID: Subject: Re: [PATCH] KVM: VMX: Fix invalid guest state detection after task-switch emulation To: Paolo Bonzini Cc: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , "linux-kernel@vger.kernel.org" , kvm , Wanpeng Li , Nadav Amit Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by nfs id v6CDpAt5002714 Content-Length: 2308 Lines: 57 2017-07-12 0:09 GMT+08:00 Paolo Bonzini : > On 11/07/2017 17:54, Radim Krčmář wrote: >> 2017-07-11 00:13-0700, Wanpeng Li: >>> From: Wanpeng Li >>> >>> This can be reproduced by EPT=1, unrestricted_guest=N, emulate_invalid_state=Y >>> or EPT=0, the trace of kvm-unit-tests/taskswitch2.flat is like below, it tries >>> to emulate invalid guest state task-switch: >>> >>> kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0 >>> kvm_emulate_insn: 42000:0:0f 0b (0x2) >>> kvm_emulate_insn: 42000:0:0f 0b (0x2) failed >>> kvm_inj_exception: #UD (0x0) >>> kvm_entry: vcpu 0 >>> kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0 >>> kvm_emulate_insn: 42000:0:0f 0b (0x2) >>> kvm_emulate_insn: 42000:0:0f 0b (0x2) failed >>> kvm_inj_exception: #UD (0x0) >>> ...................... >>> >>> It appears that the task-switch emulation updates rflags (and vm86 >>> flag) only after the segments are loaded, causing vmx->emulation_required >>> to be set, when in fact invalid guest state emulation is not needed. >>> >>> This patch fixes it by updating vmx->emulation_required after the >>> rflags (and vm86 flag) is updated in task-switch emulation. >>> >>> Suggested-by: Nadav Amit >>> Cc: Paolo Bonzini >>> Cc: Radim Krčmář >>> Cc: Nadav Amit >>> Signed-off-by: Wanpeng Li >>> --- >>> arch/x86/kvm/vmx.c | 1 + >>> 1 file changed, 1 insertion(+) >>> >>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >>> index f50cbfd..70270a2 100644 >>> --- a/arch/x86/kvm/vmx.c >>> +++ b/arch/x86/kvm/vmx.c >>> @@ -6255,6 +6255,7 @@ static int handle_task_switch(struct kvm_vcpu *vcpu) >>> * TODO: What about debug traps on tss switch? >>> * Are we supposed to inject them and update dr6? >>> */ >>> + vmx->emulation_required = emulation_required(vcpu); >> >> Hm, so the problem happened because changes to rflags can flip the value >> of emulation_required(). I would add this line to vmx_set_rflags() to >> make sure that we fixed everything, thanks. > > Note that there is some extra complication, because emulation_required > is expensive and you'll want to run it only when EFLAGS.VM changes. Agreed. Regards, Wanpeng Li