s390x/pv: Convert to ram_block_discard_disable()

Discarding RAM does not work as expected with protected VMs. Let's
switch to ram_block_discard_disable() for now, as we want to get rid
of qemu_balloon_inhibit(). Note that it will currently never fail, but
might fail in the future with new technologies (e.g., virtio-mem).
Acked-by: NCornelia Huck <cohuck@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Cornelia Huck <cohuck@redhat.com>
Cc: Halil Pasic <pasic@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: NDavid Hildenbrand <david@redhat.com>
Message-Id: <20200626072248.78761-6-david@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/s390x/s390-virtio-ccw.c

@@ -43,7 +43,6 @@
 #include "hw/qdev-properties.h"
 #include "hw/s390x/tod.h"
 #include "sysemu/sysemu.h"
-#include "sysemu/balloon.h"
 #include "hw/s390x/pv.h"
 #include "migration/blocker.h"
 
@@ -329,7 +328,7 @@ static void s390_machine_unprotect(S390CcwMachineState *ms)
     ms->pv = false;
     migrate_del_blocker(pv_mig_blocker);
     error_free_or_abort(&pv_mig_blocker);
-    qemu_balloon_inhibit(false);
+    ram_block_discard_disable(false);
 }
 
 static int s390_machine_protect(S390CcwMachineState *ms)
@@ -338,17 +337,22 @@ static int s390_machine_protect(S390CcwMachineState *ms)
     int rc;
 
    /*
-    * Ballooning on protected VMs needs support in the guest for
-    * sharing and unsharing balloon pages. Block ballooning for
-    * now, until we have a solution to make at least Linux guests
-    * either support it or fail gracefully.
+    * Discarding of memory in RAM blocks does not work as expected with
+    * protected VMs. Sharing and unsharing pages would be required. Disable
+    * it for now, until until we have a solution to make at least Linux
+    * guests either support it (e.g., virtio-balloon) or fail gracefully.
     */
-    qemu_balloon_inhibit(true);
+    rc = ram_block_discard_disable(true);
+    if (rc) {
+        error_report("protected VMs: cannot disable RAM discard");
+        return rc;
+    }
+
     error_setg(&pv_mig_blocker,
                "protected VMs are currently not migrateable.");
     rc = migrate_add_blocker(pv_mig_blocker, &local_err);
     if (rc) {
-        qemu_balloon_inhibit(false);
+        ram_block_discard_disable(false);
         error_report_err(local_err);
         error_free_or_abort(&pv_mig_blocker);
         return rc;
@@ -357,7 +361,7 @@ static int s390_machine_protect(S390CcwMachineState *ms)
     /* Create SE VM */
     rc = s390_pv_vm_enable();
     if (rc) {
-        qemu_balloon_inhibit(false);
+        ram_block_discard_disable(false);
         migrate_del_blocker(pv_mig_blocker);
         error_free_or_abort(&pv_mig_blocker);
         return rc;