From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752566AbeDDRJ3 (ORCPT ); Wed, 4 Apr 2018 13:09:29 -0400 Received: from mail-wm0-f68.google.com ([74.125.82.68]:40887 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752100AbeDDRJ1 (ORCPT ); Wed, 4 Apr 2018 13:09:27 -0400 X-Google-Smtp-Source: AIpwx48HcEK/NJm0YY7VBMnXsAsvIN4B+/9AVEs9v3FkBUHCCiiCtQc1JMrfJKvsMnDMfUDbG+KgpQ== Subject: Re: [PATCH v5 2/2] KVM: X86: Add Force Emulation Prefix for "emulate the next instruction" To: Wanpeng Li , David Hildenbrand Cc: LKML , kvm , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Andrew Cooper , Konrad Rzeszutek Wilk , Liran Alon References: <1522798129-14588-1-git-send-email-wanpengli@tencent.com> <1522798129-14588-3-git-send-email-wanpengli@tencent.com> <48d06146-f508-e883-72cb-881e043f9c72@redhat.com> From: Paolo Bonzini Openpgp: preference=signencrypt Autocrypt: addr=pbonzini@redhat.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/04/2018 15:35, Wanpeng Li wrote: > 2018-04-04 19:59 GMT+08:00 David Hildenbrand : >> >>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >>> index 1eb495e..a55ecef 100644 >>> --- a/arch/x86/kvm/x86.c >>> +++ b/arch/x86/kvm/x86.c >>> @@ -146,6 +146,9 @@ bool __read_mostly enable_vmware_backdoor = false; >>> module_param(enable_vmware_backdoor, bool, S_IRUGO); >>> EXPORT_SYMBOL_GPL(enable_vmware_backdoor); >>> >>> +static bool __read_mostly force_emulation_prefix = false; >>> +module_param(force_emulation_prefix, bool, S_IRUGO); >>> + >>> #define KVM_NR_SHARED_MSRS 16 >>> >>> struct kvm_shared_msrs_global { >>> @@ -4844,6 +4847,21 @@ int handle_ud(struct kvm_vcpu *vcpu) >>> { >>> enum emulation_result er; >>> >>> + if (force_emulation_prefix) { >>> + char sig[5]; /* ud2; .ascii "kvm" */ >>> + struct x86_exception e; >>> + >>> + if (kvm_read_guest_virt(&vcpu->arch.emulate_ctxt, >>> + kvm_get_linear_rip(vcpu), sig, sizeof(sig), &e)) >>> + goto emulate_ud; >>> + >>> + if (memcmp(sig, "\xf\xbkvm", sizeof(sig)) == 0) { >>> + kvm_rip_write(vcpu, kvm_rip_read(vcpu) + sizeof(sig)); >>> + return emulate_instruction(vcpu, 0) == EMULATE_DONE; >> >> What if we would have an invalid instruction here? Shouldn't you handle >> the emulate_instruction() like below? >> (e.g. keep a variable with the emulation type (0 vs EMULTYPE_TRAP_UD) >> and reuse emulate_ud below) > > emulate_instruction(vcpu, 0) can handle invalid instruction. But David's observation is still better because your code doesn't handle usermode exits. I've fixed this up. Paolo