s390x: Expose pv attribute in QOM

People doing VM management requested a way to query if a VM is in PV
or not. So this patch exposes the runtime PV attribute which is true
once the VM successfully made the switch into PV mode (according to
KVM) and did not yet reboot to drop out of it.

This of course does never replace attestation, it's merely QEMU's view
of the situation.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
CC: Hendrik Brueckner <brueckner@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.ibm.com>
Link: https://lore.kernel.org/qemu-devel/20260924142846.157848-1-frankja@linux.ibm.com
Signed-off-by: Eric Farman <farman@linux.ibm.com>

docs/system/s390x/protvirt.rst

@@ -65,3 +65,14 @@ metadata. In case this boot method is used, the command line
 options -initrd and -cmdline are ineffective. The preparation of a PVM
 image is done via the ``genprotimg`` tool from the s390-tools
 collection.
+
+
+PV property
+-----------
+
+The s390x-ccw machine exposes the read-only runtime "pv"
+property. This property is true if a guest successfully made the
+transition into PV mode as reported by KVM and hasn't yet exited PV
+mode via a reboot. This does not replace PV attestation which is the
+only authoritative way to get a definitive answer if a guest is truly
+protected.

hw/s390x/s390-virtio-ccw.c

@@ -838,6 +838,13 @@ static inline void machine_set_secure_boot(Object *obj, bool value,
     ms->secure_boot = value;
 }
 
+static inline bool machine_get_pv(Object *obj, Error **errp)
+{
+    S390CcwMachineState *ms = S390_CCW_MACHINE(obj);
+
+    return ms->pv;
+}
+
  /*
   * S390x-specific global compatibility properties.
   *
@@ -919,6 +926,12 @@ static void ccw_machine_class_init(ObjectClass *oc, const void *data)
                                    machine_set_secure_boot);
     object_class_property_set_description(oc, "secure-boot",
             "enable/disable secure boot");
+
+    object_class_property_add_bool(oc, "pv",
+                                   machine_get_pv,
+                                   NULL);
+    object_class_property_set_description(oc, "pv",
+            "true while the guest runs in protected virtualization mode (read-only)");
 }
 
 static inline void s390_machine_initfn(Object *obj)