Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934278AbdGTIEX (ORCPT ); Thu, 20 Jul 2017 04:04:23 -0400 Received: from mail-oi0-f68.google.com ([209.85.218.68]:36447 "EHLO mail-oi0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934218AbdGTIER (ORCPT ); Thu, 20 Jul 2017 04:04:17 -0400 MIME-Version: 1.0 In-Reply-To: <20170720075705.GA30711@potion> References: <1500507602-105830-1-git-send-email-wanpeng.li@hotmail.com> <20170720075705.GA30711@potion> From: Wanpeng Li Date: Thu, 20 Jul 2017 16:04:16 +0800 Message-ID: Subject: Re: [PATCH v2] KVM: VMX: Fix invalid guest state detection after task-switch emulation To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= Cc: "linux-kernel@vger.kernel.org" , kvm , Paolo Bonzini , 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 v6K84TaS003556 Content-Length: 2412 Lines: 61 2017-07-20 15:57 GMT+08:00 Radim Krčmář : > 2017-07-19 16:40-0700, 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. >> >> Thanks Radim for moving the update to vmx__set_flags and adding Paolo's >> suggestion for the check. >> >> Suggested-by: Nadav Amit >> Cc: Paolo Bonzini >> Cc: Radim Krčmář >> Cc: Nadav Amit >> Signed-off-by: Wanpeng Li >> --- >> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >> static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags) >> { >> + unsigned long old_rflags = vmx_get_rflags(vcpu); >> + unsigned long save_rflags = rflags; >> + >> __set_bit(VCPU_EXREG_RFLAGS, (ulong *)&vcpu->arch.regs_avail); >> to_vmx(vcpu)->rflags = rflags; >> if (to_vmx(vcpu)->rmode.vm86_active) { >> @@ -2370,6 +2378,9 @@ static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags) >> rflags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM; >> } >> vmcs_writel(GUEST_RFLAGS, rflags); >> + >> + if ((old_rflags ^ save_rflags) & X86_EFLAGS_VM) > > Looks good, thanks to both. > > The desired rflags are saved in to_vmx(vcpu)->rflags, so we don't need > the temporary variable -- would using that or vmx_get_rflags(vcpu) > generate worse code? Yeah, I will send out a newer version. Regards, Wanpeng Li