[PULL 05/27] hw/vfio/ap: Storing event information for an AP configuration change event

["Cédric Le Goater" <clg@redhat.com>]

From: Rorie Reyes <rreyes@linux.ibm.com>

These functions can be invoked by the function that handles interception
of the CHSC SEI instruction for requests indicating the accessibility of
one or more adjunct processors has changed.

Signed-off-by: Rorie Reyes <rreyes@linux.ibm.com>
Reviewed-by: Anthony Krowiak <akrowiak@linux.ibm.com>
Link: https://lore.kernel.org/qemu-devel/20250609164418.17585-4-rreyes@linux.ibm.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>
---
 include/hw/s390x/ap-bridge.h | 39 +++++++++++++++++++++++++++++++++++
 hw/vfio/ap.c                 | 40 ++++++++++++++++++++++++++++++++++++
 2 files changed, 79 insertions(+)

diff --git a/include/hw/s390x/ap-bridge.h b/include/hw/s390x/ap-bridge.h
index 470e439a98ed5306dadb29f7507ca880756eb13f..7efc52928db15c429b2486e09e701b5cc4a799f2 100644
--- a/include/hw/s390x/ap-bridge.h
+++ b/include/hw/s390x/ap-bridge.h
@@ -16,4 +16,43 @@
 
 void s390_init_ap(void);
 
+typedef struct ChscSeiNt0Res {
+    uint16_t length;
+    uint16_t code;
+    uint8_t reserved1;
+    uint16_t reserved2;
+    uint8_t nt;
+#define PENDING_EVENT_INFO_BITMASK 0x80;
+    uint8_t flags;
+    uint8_t reserved3;
+    uint8_t rs;
+    uint8_t cc;
+} QEMU_PACKED ChscSeiNt0Res;
+
+#define NT0_RES_RESPONSE_CODE 1
+#define NT0_RES_NT_DEFAULT    0
+#define NT0_RES_RS_AP_CHANGE  5
+#define NT0_RES_CC_AP_CHANGE  3
+
+#define EVENT_INFORMATION_NOT_STORED 1
+#define EVENT_INFORMATION_STORED     0
+
+/**
+ * ap_chsc_sei_nt0_get_event - Retrieve the next pending AP config
+ * change event
+ * @res: Pointer to a ChscSeiNt0Res struct to be filled with event
+ * data
+ *
+ * This function checks for any pending AP config change events and,
+ * if present, populates the provided response structure with the
+ * appropriate SEI NT0 fields.
+ *
+ * Return:
+ *   EVENT_INFORMATION_STORED - An event was available and written to @res
+ *   EVENT_INFORMATION_NOT_STORED - No event was available
+ */
+int ap_chsc_sei_nt0_get_event(void *res);
+
+bool ap_chsc_sei_nt0_have_event(void);
+
 #endif
diff --git a/hw/vfio/ap.c b/hw/vfio/ap.c
index 681fd4a4f1cb861cb287fca9ce2134e55ec20323..874e0d1eaf1dafa105f9f42705e9973ffc719803 100644
--- a/hw/vfio/ap.c
+++ b/hw/vfio/ap.c
@@ -10,6 +10,7 @@
  * directory.
  */
 
+#include <stdbool.h>
 #include "qemu/osdep.h"
 #include CONFIG_DEVICES /* CONFIG_IOMMUFD */
 #include <linux/vfio.h>
@@ -101,6 +102,38 @@ static void vfio_ap_cfg_chg_notifier_handler(void *opaque)
 
 }
 
+int ap_chsc_sei_nt0_get_event(void *res)
+{
+    ChscSeiNt0Res *nt0_res  = (ChscSeiNt0Res *)res;
+    APConfigChgEvent *cfg_chg_event;
+
+    WITH_QEMU_LOCK_GUARD(&cfg_chg_events_lock) {
+        if (QTAILQ_EMPTY(&cfg_chg_events)) {
+            return EVENT_INFORMATION_NOT_STORED;
+        }
+
+        cfg_chg_event = QTAILQ_FIRST(&cfg_chg_events);
+        QTAILQ_REMOVE(&cfg_chg_events, cfg_chg_event, next);
+    }
+
+    memset(nt0_res, 0, sizeof(*nt0_res));
+    g_free(cfg_chg_event);
+    nt0_res->flags |= PENDING_EVENT_INFO_BITMASK;
+    nt0_res->length = sizeof(ChscSeiNt0Res);
+    nt0_res->code = NT0_RES_RESPONSE_CODE;
+    nt0_res->nt = NT0_RES_NT_DEFAULT;
+    nt0_res->rs = NT0_RES_RS_AP_CHANGE;
+    nt0_res->cc = NT0_RES_CC_AP_CHANGE;
+
+    return EVENT_INFORMATION_STORED;
+}
+
+bool ap_chsc_sei_nt0_have_event(void)
+{
+    QEMU_LOCK_GUARD(&cfg_chg_events_lock);
+    return !QTAILQ_EMPTY(&cfg_chg_events);
+}
+
 static bool vfio_ap_register_irq_notifier(VFIOAPDevice *vapdev,
                                           unsigned int irq, Error **errp)
 {
@@ -197,6 +230,13 @@ static void vfio_ap_realize(DeviceState *dev, Error **errp)
     VFIOAPDevice *vapdev = VFIO_AP_DEVICE(dev);
     VFIODevice *vbasedev = &vapdev->vdev;
 
+    static bool lock_initialized;
+
+    if (!lock_initialized) {
+        qemu_mutex_init(&cfg_chg_events_lock);
+        lock_initialized = true;
+    }
+
     if (!vfio_device_get_name(vbasedev, errp)) {
         return;
     }
-- 
2.49.0