From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [RFC PATCH 4/4] KVM: vmx: add support for emulating UMIP Date: Wed, 13 Jul 2016 11:35:53 +0200 Message-ID: <4e7bab78-61cf-271e-9fb9-685d217f8d0d@redhat.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit To: Yang Zhang , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Return-path: 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 In-Reply-To: <8f893604-1e80-2979-bc87-45a049238e58@gmail.com> Sender: kvm-owner@vger.kernel.org List-ID: 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