KVM: x86: Exit to userspace on emulation skip failure

Kill a few birds with one stone by forcing an exit to userspace on skip
emulation failure.  This removes a reference to EMULATE_FAIL, fixes a
bug in handle_ept_misconfig() where it would exit to userspace without
setting run->exit_reason, and fixes a theoretical bug in SVM's
task_switch_interception() where it would overwrite run->exit_reason on
a return of EMULATE_USER_EXIT.

Note, this technically doesn't fully fix task_switch_interception()
as it now incorrectly handles EMULATE_FAIL, but in practice there is no
bug as EMULATE_FAIL will never be returned for EMULTYPE_SKIP.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm.c

@@ -3885,8 +3885,8 @@ static int task_switch_interception(struct vcpu_svm *svm)
 	    int_type == SVM_EXITINTINFO_TYPE_SOFT ||
 	    (int_type == SVM_EXITINTINFO_TYPE_EXEPT &&
 	     (int_vec == OF_VECTOR || int_vec == BP_VECTOR))) {
-		if (skip_emulated_instruction(&svm->vcpu) != EMULATE_DONE)
-			goto fail;
+		if (skip_emulated_instruction(&svm->vcpu) == EMULATE_USER_EXIT)
+			return 0;
 	}
 
 	if (int_type != SVM_EXITINTINFO_TYPE_SOFT)

arch/x86/kvm/x86.c

@@ -6306,6 +6306,13 @@ static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type)
 		return EMULATE_DONE;
 	}
 
+	if (emulation_type & EMULTYPE_SKIP) {
+		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+		vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
+		vcpu->run->internal.ndata = 0;
+		return EMULATE_USER_EXIT;
+	}
+
 	kvm_queue_exception(vcpu, UD_VECTOR);
 
 	if (!is_guest_mode(vcpu) && kvm_x86_ops->get_cpl(vcpu) == 0) {
@@ -6641,8 +6648,6 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
 				inject_emulated_exception(vcpu);
 				return EMULATE_DONE;
 			}
-			if (emulation_type & EMULTYPE_SKIP)
-				return EMULATE_FAIL;
 			return handle_emulation_failure(vcpu, emulation_type);
 		}
 	}