From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH] KVM: nVMX: Leave VMX mode on clearing of feature control MSR Date: Wed, 18 Dec 2013 10:23:35 +0100 Message-ID: <52B16997.9010907@redhat.com> References: <52B09EA7.4040507@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Gleb Natapov , kvm To: Jan Kiszka Return-path: Received: from mail-ea0-f181.google.com ([209.85.215.181]:53866 "EHLO mail-ea0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750910Ab3LRJXl (ORCPT ); Wed, 18 Dec 2013 04:23:41 -0500 Received: by mail-ea0-f181.google.com with SMTP id m10so3373634eaj.26 for ; Wed, 18 Dec 2013 01:23:40 -0800 (PST) In-Reply-To: <52B09EA7.4040507@siemens.com> Sender: kvm-owner@vger.kernel.org List-ID: Il 17/12/2013 19:57, Jan Kiszka ha scritto: > When userspace sets MSR_IA32_FEATURE_CONTROL to 0, make sure we leave > root and non-root mode, fully disabling VMX. The register state of the > VCPU is undefined after this step, so userspace has to set it to a > proper state afterward. > > This enables to reboot a VM while it is running some hypervisor code. > > Signed-off-by: Jan Kiszka > --- > > Even without a QEMU patch, this already enables system reset - the guest > is left in such a broken state that it simply triple-faults and resets > twice. Nevertheless, QEMU patch will follow. > > arch/x86/kvm/vmx.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index f90320b..6a0c2fa 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -2455,6 +2455,8 @@ static int vmx_get_vmx_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 *pdata) > return 1; > } > > +static void vmx_leave_nested(struct kvm_vcpu *vcpu); > + > static int vmx_set_vmx_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > { > u32 msr_index = msr_info->index; > @@ -2470,6 +2472,8 @@ static int vmx_set_vmx_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > & FEATURE_CONTROL_LOCKED) > return 0; > to_vmx(vcpu)->nested.msr_ia32_feature_control = data; > + if (host_initialized && data == 0) > + vmx_leave_nested(vcpu); > return 1; > } > > @@ -8488,6 +8492,16 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu) > } > > /* > + * Forcibly leave nested mode in order to be able to reset the VCPU later on. > + */ > +static void vmx_leave_nested(struct kvm_vcpu *vcpu) > +{ > + if (is_guest_mode(vcpu)) > + nested_vmx_vmexit(vcpu); > + free_nested(to_vmx(vcpu)); > +} > + > +/* > * L1's failure to enter L2 is a subset of a normal exit, as explained in > * 23.7 "VM-entry failures during or after loading guest state" (this also > * lists the acceptable exit-reason and exit-qualification parameters). > Applied, thanks! Paolo