Handle interception of the CHSC SEI instruction for requests
indicating the guest's AP configuration has changed.

If configuring -without-defaul-devices, hw/vfio/ap-sub.c
was created to handle such circumstance. Also added if
CONFIG_VFIO_AP is false, it will use the stub file.

Signed-off-by: Rorie Reyes <rreyes@linux.ibm.com>
Reviewed-by: Anthony Krowiak <akrowiak@linux.ibm.com>
Tested-by: Anthony Krowiak <akrowiak@linux.ibm.com>
---
 MAINTAINERS           |  1 +
 hw/vfio/ap-stub.c     | 23 +++++++++++++++++++++++
 hw/vfio/meson.build   |  1 +
 target/s390x/ioinst.c | 11 +++++++++--
 4 files changed, 34 insertions(+), 2 deletions(-)
 create mode 100644 hw/vfio/ap-stub.c

diff --git a/MAINTAINERS b/MAINTAINERS
index d54b5578f8..45229837d1 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -112,6 +112,7 @@ F: hw/intc/s390_flic.c
 F: hw/intc/s390_flic_kvm.c
 F: hw/s390x/
 F: hw/vfio/ap.c
+F: hw/vfio/ap-stub.c
 F: hw/vfio/ccw.c
 F: hw/watchdog/wdt_diag288.c
 F: include/hw/s390x/
diff --git a/hw/vfio/ap-stub.c b/hw/vfio/ap-stub.c
new file mode 100644
index 0000000000..9d2c4c2e67
--- /dev/null
+++ b/hw/vfio/ap-stub.c
@@ -0,0 +1,23 @@
+/*
+ * VFIO based AP matrix device assignment
+ *
+ * Copyright 2025 IBM Corp.
+ * Author(s): Rorie Reyes <rreyes@linux.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or (at
+ * your option) any later version. See the COPYING file in the top-level
+ * directory.
+ */
+
+#include "qemu/osdep.h"
+#include "hw/s390x/ap-bridge.h"
+
+int ap_chsc_sei_nt0_get_event(void *res)
+{
+    return 0;
+}
+
+int ap_chsc_sei_nt0_have_event(void)
+{
+    return 0;
+}
diff --git a/hw/vfio/meson.build b/hw/vfio/meson.build
index a8939c8386..28f4c959b8 100644
--- a/hw/vfio/meson.build
+++ b/hw/vfio/meson.build
@@ -11,6 +11,7 @@ vfio_ss.add(when: 'CONFIG_VFIO_PCI', if_true: files(
 vfio_ss.add(when: 'CONFIG_VFIO_CCW', if_true: files('ccw.c'))
 vfio_ss.add(when: 'CONFIG_VFIO_PLATFORM', if_true: files('platform.c'))
 vfio_ss.add(when: 'CONFIG_VFIO_AP', if_true: files('ap.c'))
+vfio_ss.add(when: 'CONFIG_VFIO_AP', if_false: files('ap-stub.c'))
 vfio_ss.add(when: 'CONFIG_VFIO_IGD', if_true: files('igd.c'))
 
 specific_ss.add_all(when: 'CONFIG_VFIO', if_true: vfio_ss)
diff --git a/target/s390x/ioinst.c b/target/s390x/ioinst.c
index a944f16c25..f061c6db14 100644
--- a/target/s390x/ioinst.c
+++ b/target/s390x/ioinst.c
@@ -17,6 +17,7 @@
 #include "trace.h"
 #include "hw/s390x/s390-pci-bus.h"
 #include "target/s390x/kvm/pv.h"
+#include "hw/s390x/ap-bridge.h"
 
 /* All I/O instructions but chsc use the s format */
 static uint64_t get_address_from_regs(CPUS390XState *env, uint32_t ipb,
@@ -573,13 +574,19 @@ out:
 
 static int chsc_sei_nt0_get_event(void *res)
 {
-    /* no events yet */
+    if (s390_has_feat(S390_FEAT_AP)) {
+        return ap_chsc_sei_nt0_get_event(res);
+    }
+
     return 1;
 }
 
 static int chsc_sei_nt0_have_event(void)
 {
-    /* no events yet */
+    if (s390_has_feat(S390_FEAT_AP)) {
+        return ap_chsc_sei_nt0_have_event();
+    }
+
     return 0;
 }
 
-- 
2.48.1