From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752118AbcGMJgZ (ORCPT ); Wed, 13 Jul 2016 05:36:25 -0400 Received: from mail-lf0-f68.google.com ([209.85.215.68]:36643 "EHLO mail-lf0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751616AbcGMJgN (ORCPT ); Wed, 13 Jul 2016 05:36:13 -0400 Subject: Re: [RFC PATCH 4/4] KVM: vmx: add support for emulating UMIP To: Yang Zhang , linux-kernel@vger.kernel.org, kvm@vger.kernel.org References: <1468351223-3250-1-git-send-email-pbonzini@redhat.com> <1468351223-3250-5-git-send-email-pbonzini@redhat.com> <8f893604-1e80-2979-bc87-45a049238e58@gmail.com> From: Paolo Bonzini Message-ID: <4e7bab78-61cf-271e-9fb9-685d217f8d0d@redhat.com> Date: Wed, 13 Jul 2016 11:35:53 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: <8f893604-1e80-2979-bc87-45a049238e58@gmail.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13/07/2016 11:21, Yang Zhang wrote: >> >> +static int handle_desc(struct kvm_vcpu *vcpu) >> +{ >> + WARN_ON(!(vcpu->arch.cr4 & X86_CR4_UMIP)); > > I think WARN_ON is too heavy since a malicious guest may trigger it always. I missed this---how so? Setting the bit is under "if ((cr4 & X86_CR4_UMIP) && !boot_cpu_has(X86_FEATURE_UMIP))". Paolo