From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bandan Das Subject: Re: [PATCH] vt-x: Preserve host CR4.MCE value while in guest mode. Date: Thu, 16 Apr 2015 14:44:54 -0400 Message-ID: References: <552FEAAD.6000600@siemens.com> <1429208106-11759-1-git-send-email-serebrin@google.com> Mime-Version: 1.0 Content-Type: text/plain Cc: kvm@vger.kernel.org, stable@vger.kernel.org, luto@amacapital.net, pbonzini@redhat.com, jan.kiszka@siemens.com To: Ben Serebrin Return-path: In-Reply-To: <1429208106-11759-1-git-send-email-serebrin@google.com> (Ben Serebrin's message of "Thu, 16 Apr 2015 11:15:06 -0700") Sender: stable-owner@vger.kernel.org List-Id: kvm.vger.kernel.org Ben Serebrin writes: I suggest changing the subject to KVM: VMX: Preserve host CR4.MCE value while in guest mode That keeps it consistent with the $SUBJECT naming convention KVM follows. If Paolo is ok with changing it in his tree directly, that's fine too. Bandan > 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); > > if (cr4 & X86_CR4_VMXE) { > /*