Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751773AbdGIHaW (ORCPT ); Sun, 9 Jul 2017 03:30:22 -0400 Received: from mail-oi0-f52.google.com ([209.85.218.52]:34502 "EHLO mail-oi0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750765AbdGIHaU (ORCPT ); Sun, 9 Jul 2017 03:30:20 -0400 MIME-Version: 1.0 From: Wanpeng Li Date: Sun, 9 Jul 2017 15:30:19 +0800 Message-ID: Subject: RFC: Task switch emulation fails for VM86 mode To: Paolo Bonzini , Radim Krcmar Cc: kvm , "linux-kernel@vger.kernel.org" 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-Length: 2661 Lines: 77 Hi all, I found that task switch emulation fails to work for VM86 mode if guest state is invalid. It can be reproduced by running kvm-unit-tests/taskswitch2.flat, EPT = 0 or EPT=1, unrestricted_guest=N, emulate_invalid_guest_state=Y. When EPT=1, unrestricted_guest=Y, emulate_invalid_state=Y, the trace of kvm-unit-tests/taskswitch2.flat is like below: kvm_entry: vcpu 0 kvm_exit: reason TASK_SWITCH rip 0x4008d0 info 40000058 0 kvm_entry: vcpu 0 kvm_exit: reason EXCEPTION_NMI rip 0x0 info 0 80000306 kvm_emulate_insn: 42000:0:0f 0b (0x2) kvm_inj_exception: #UD (0x0) kvm_entry: vcpu 0 kvm_exit: reason TASK_SWITCH rip 0x0 info c0000050 0 kvm_entry: vcpu 0 When EPT=1, unrestricted_guest=Y, emulate_invalid_state=Y, the trace of kvm-unit-tests/taskswitch2.flat is like below, when emulating "0f 0b(#UD)" fails, it injects another #UD and triggers a task switch in the kvm-unit-tests/taskswitch2.flat again. 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) 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) ..................... Then I try to add the task switch emulation in the handle_invalid_guest_state() path, however, I will get TRIPLE FAULT. diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index f76efad..758f728 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -6312,11 +6312,15 @@ static int handle_invalid_guest_state(struct kvm_vcpu *vcpu) u32 cpu_exec_ctrl; bool intr_window_requested; unsigned count = 130; + u32 exit_reason = vmx->exit_reason; cpu_exec_ctrl = vmcs_read32(CPU_BASED_VM_EXEC_CONTROL); intr_window_requested = cpu_exec_ctrl & CPU_BASED_VIRTUAL_INTR_PENDING; while (vmx->emulation_required && count-- != 0) { + if (exit_reason == EXIT_REASON_TASK_SWITCH) + return handle_task_switch(vcpu); + if (intr_window_requested && vmx_interrupt_allowed(vcpu)) return handle_interrupt_window(&vmx->vcpu); kvm_exit: reason TASK_SWITCH rip 0x4008d0 info 40000058 0 kvm_entry: vcpu 0 kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0 kvm_entry: vcpu 0 kvm_exit: reason TRIPLE_FAULT rip 0xffff info 0 0 kvm_userspace_exit: reason KVM_EXIT_SHUTDOWN (8) Any proposal is a great appreciated. :) Regards, Wanpeng Li