KVM: x86: Emulator support for #UD on CPL>0

Certain instructions (e.g., mwait and monitor) cause a #UD exception when they
are executed in user mode. This is in contrast to the regular privileged
instructions which cause #GP. In order not to mess with SVM interception of
mwait and monitor which assumes privilege level assertions take place before
interception, a flag has been added.
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/emulate.c

@@ -165,6 +165,7 @@
 #define Intercept   ((u64)1 << 48)  /* Has valid intercept field */
 #define CheckPerm   ((u64)1 << 49)  /* Has valid check_perm field */
 #define NoBigReal   ((u64)1 << 50)  /* No big real mode */
+#define PrivUD      ((u64)1 << 51)  /* #UD instead of #GP on CPL > 0 */
 
 #define DstXacc     (DstAccLo | SrcAccHi | SrcWrite)
 
@@ -4608,7 +4609,10 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
 
 		/* Privileged instruction can be executed only in CPL=0 */
 		if ((ctxt->d & Priv) && ops->cpl(ctxt)) {
-			rc = emulate_gp(ctxt, 0);
+			if (ctxt->d & PrivUD)
+				rc = emulate_ud(ctxt);
+			else
+				rc = emulate_gp(ctxt, 0);
 			goto done;
 		}