kvm: nVMX: reflect MTF VM-exits if injected by L1

According to SDM 26.6.2, it is possible to inject an MTF VM-exit via the
VM-entry interruption-information field regardless of the 'monitor trap
flag' VM-execution control. KVM appropriately copies the VM-entry
interruption-information field from vmcs12 to vmcs02. However, if L1
has not set the 'monitor trap flag' VM-execution control, KVM fails to
reflect the subsequent MTF VM-exit into L1.

Fix this by consulting the VM-entry interruption-information field of
vmcs12 to determine if L1 has injected the MTF VM-exit. If so, reflect
the exit, regardless of the 'monitor trap flag' VM-execution control.

Fixes: 5f3d45e7 ("kvm/x86: add support for MONITOR_TRAP_FLAG")
Signed-off-by: Oliver Upton <oupton@google.com>
Reviewed-by: Peter Shier <pshier@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Message-Id: <20200414224746.240324-1-oupton@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -5533,6 +5533,23 @@ static bool nested_vmx_exit_handled_vmcs_access(struct kvm_vcpu *vcpu,
 	return 1 & (b >> (field & 7));
 }
 
+static bool nested_vmx_exit_handled_mtf(struct vmcs12 *vmcs12)
+{
+	u32 entry_intr_info = vmcs12->vm_entry_intr_info_field;
+
+	if (nested_cpu_has_mtf(vmcs12))
+		return true;
+
+	/*
+	 * An MTF VM-exit may be injected into the guest by setting the
+	 * interruption-type to 7 (other event) and the vector field to 0. Such
+	 * is the case regardless of the 'monitor trap flag' VM-execution
+	 * control.
+	 */
+	return entry_intr_info == (INTR_INFO_VALID_MASK
+				   | INTR_TYPE_OTHER_EVENT);
+}
+
 /*
  * Return 1 if we should exit from L2 to L1 to handle an exit, or 0 if we
  * should handle it ourselves in L0 (and then continue L2). Only call this
@@ -5633,7 +5650,7 @@ bool nested_vmx_exit_reflected(struct kvm_vcpu *vcpu, u32 exit_reason)
 	case EXIT_REASON_MWAIT_INSTRUCTION:
 		return nested_cpu_has(vmcs12, CPU_BASED_MWAIT_EXITING);
 	case EXIT_REASON_MONITOR_TRAP_FLAG:
-		return nested_cpu_has_mtf(vmcs12);
+		return nested_vmx_exit_handled_mtf(vmcs12);
 	case EXIT_REASON_MONITOR_INSTRUCTION:
 		return nested_cpu_has(vmcs12, CPU_BASED_MONITOR_EXITING);
 	case EXIT_REASON_PAUSE_INSTRUCTION: