KVM: x86: work around infinite loop in microcode when #AC is delivered

It was found that a guest can DoS a host by triggering an infinite
stream of "alignment check" (#AC) exceptions.  This causes the
microcode to enter an infinite loop where the core never receives
another interrupt.  The host kernel panics pretty quickly due to the
effects (CVE-2015-5307).

Signed-off-by: Eric Northup <digitaleric@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
static void vmx_inject_page_fault_nested(struct kvm_vcpu *vcpu,
		struct x86_exception *fault)
{
	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);

	WARN_ON(!is_guest_mode(vcpu));

	if (nested_vmx_is_page_fault_vmexit(vmcs12, fault->error_code))
		nested_vmx_vmexit(vcpu, to_vmx(vcpu)->exit_reason,
				  vmcs_read32(VM_EXIT_INTR_INFO),
				  vmcs_readl(EXIT_QUALIFICATION));
	else
		kvm_inject_page_fault(vcpu, fault);
}

static void vmx_inject_page_fault_nested(struct kvm_vcpu *vcpu,
		struct x86_exception *fault)
{
	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);

	WARN_ON(!is_guest_mode(vcpu));

	if (nested_vmx_is_page_fault_vmexit(vmcs12, fault->error_code))
		nested_vmx_vmexit(vcpu, to_vmx(vcpu)->exit_reason,
				  vmcs_read32(VM_EXIT_INTR_INFO),
				  vmcs_readl(EXIT_QUALIFICATION));
	else
		kvm_inject_page_fault(vcpu, fault);
}
