From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH] vt-x: Preserve host CR4.MCE value while in guest mode. Date: Thu, 16 Apr 2015 19:00:29 +0200 Message-ID: <552FEAAD.6000600@siemens.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit To: Benjamin Serebrin , kvm@vger.kernel.org, stable@vger.kernel.org, luto@amacapital.net, pbonzini@redhat.com Return-path: Received: from goliath.siemens.de ([192.35.17.28]:34574 "EHLO goliath.siemens.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751807AbbDPRAk (ORCPT ); Thu, 16 Apr 2015 13:00:40 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On 2015-04-16 18:41, Benjamin Serebrin wrote: > The host's decision to enable machine check exceptions should remain > in force during non-root mode. KVM was writing 0 to cr4 on VCPU reset > and passed a slightly-modified 0 to the vmcs.guest_cr4 value. > > Tested: Built. > On earlier version, tested by injecting machine check while a guest is spinning. > Before the change, if guest CR4.MCE==0, then the machine check is > escalated to Catastrophic Error (CATERR) and the machine dies. > If guest CR4.MCE==1, then the machine check causes VMEXIT and is > handled normally by host Linux. After the change, injecting a machine > check causes normal Linux machine check handling. > > Signed-off-by: Ben Serebrin > --- > arch/x86/kvm/vmx.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index f5e8dce..f7b6168 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -3622,8 +3622,16 @@ static void vmx_set_cr3(struct kvm_vcpu *vcpu, > unsigned long cr3) > > static int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4) > { > - unsigned long hw_cr4 = cr4 | (to_vmx(vcpu)->rmode.vm86_active ? > - KVM_RMODE_VM_CR4_ALWAYS_ON : KVM_PMODE_VM_CR4_ALWAYS_ON); > + /* > + * Pass through host's Machine Check Enable value to hw_cr4, which > + * is in force while we are in guest mode. Do not let guests control > + * this bit, even if host CR4.MCE == 0. > + */ > + unsigned long hw_cr4 = > + (cr4_read_shadow() & X86_CR4_MCE) | > + (cr4 & ~X86_CR4_MCE) | > + (to_vmx(vcpu)->rmode.vm86_active ? > + KVM_RMODE_VM_CR4_ALWAYS_ON : KVM_PMODE_VM_CR4_ALWAYS_ON); You lost most of your whitespaces - in the webmailer? ;) Jan > > if (cr4 & X86_CR4_VMXE) { > /* > -- Siemens AG, Corporate Technology, CT RTC ITP SES-DE Corporate Competence Center Embedded Linux