From 085e68eeafbf76e21848ad5bafaecec88a11dd64 Mon Sep 17 00:00:00 2001 From: Ben Serebrin Date: Thu, 16 Apr 2015 11:58:05 -0700 Subject: [PATCH] KVM: VMX: Preserve host CR4.MCE value while in guest mode. 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 Reviewed-by: Venkatesh Srinivas Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini --- 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 f5e8dce8046c..f7b61687bd79 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) { /* -- GitLab