s390x/kvm: Guest Migration TOD clock synchronization

Synchronizes the guest TOD clock across a migration by sending the guest TOD
clock value to the destination system. If the guest TOD clock is not preserved
across a migration then the guest's view of time will snap backwards if the
destination host clock is behind the source host clock. This will cause the
guest to hang immediately upon resuming on the destination system.

Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Jason J. Herne <jjherne@linux.vnet.ibm.com>
Signed-off-by: Jens Freimann <jfrei@linux.vnet.ibm.com>

Message-Id: <1425912968-54387-1-git-send-email-jfrei@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>

2 files changed, 56 insertions, 0 deletions

diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
index dac00cec7c..eea0742b64 100644
--- a/hw/s390x/s390-virtio-ccw.c
+++ b/hw/s390x/s390-virtio-ccw.c
@@ -181,6 +181,10 @@ static void ccw_init(MachineState *machine)
 
     /* Create VirtIO network adapters */
     s390_create_virtio_net(BUS(css_bus), "virtio-net-ccw");
+
+    /* Register savevm handler for guest TOD clock */
+    register_savevm(NULL, "todclock", 0, 1,
+                    gtod_save, gtod_load, kvm_state);
 }
 
 static void ccw_machine_class_init(ObjectClass *oc, void *data)
diff --git a/hw/s390x/s390-virtio.c b/hw/s390x/s390-virtio.c
index 412e49ba33..bdb538859f 100644
--- a/hw/s390x/s390-virtio.c
+++ b/hw/s390x/s390-virtio.c
@@ -38,6 +38,7 @@
 #include "hw/s390x/sclp.h"
 #include "hw/s390x/s390_flic.h"
 #include "hw/s390x/s390-virtio.h"
+#include "cpu.h"
 
 //#define DEBUG_S390
 
@@ -53,6 +54,9 @@
 #define ZIPL_FILENAME                   "s390-zipl.rom"
 #define TYPE_S390_MACHINE               "s390-machine"
 
+#define S390_TOD_CLOCK_VALUE_MISSING    0x00
+#define S390_TOD_CLOCK_VALUE_PRESENT    0x01
+
 static VirtIOS390Bus *s390_bus;
 static S390CPU **ipi_states;
 
@@ -196,6 +200,51 @@ void s390_create_virtio_net(BusState *bus, const char *name)
     }
 }
 
+void gtod_save(QEMUFile *f, void *opaque)
+{
+    uint64_t tod_low;
+    uint8_t tod_high;
+    int r;
+
+    r = s390_get_clock(&tod_high, &tod_low);
+    if (r) {
+        fprintf(stderr, "WARNING: Unable to get guest clock for migration. "
+                        "Error code %d. Guest clock will not be migrated "
+                        "which could cause the guest to hang.\n", r);
+        qemu_put_byte(f, S390_TOD_CLOCK_VALUE_MISSING);
+        return;
+    }
+
+    qemu_put_byte(f, S390_TOD_CLOCK_VALUE_PRESENT);
+    qemu_put_byte(f, tod_high);
+    qemu_put_be64(f, tod_low);
+}
+
+int gtod_load(QEMUFile *f, void *opaque, int version_id)
+{
+    uint64_t tod_low;
+    uint8_t tod_high;
+    int r;
+
+    if (qemu_get_byte(f) == S390_TOD_CLOCK_VALUE_MISSING) {
+        fprintf(stderr, "WARNING: Guest clock was not migrated. This could "
+                        "cause the guest to hang.\n");
+        return 0;
+    }
+
+    tod_high = qemu_get_byte(f);
+    tod_low = qemu_get_be64(f);
+
+    r = s390_set_clock(&tod_high, &tod_low);
+    if (r) {
+        fprintf(stderr, "WARNING: Unable to set guest clock value. "
+                        "s390_get_clock returned error %d. This could cause "
+                        "the guest to hang.\n", r);
+    }
+
+    return 0;
+}
+
 /* PC hardware initialisation */
 static void s390_init(MachineState *machine)
 {
@@ -253,6 +302,9 @@ static void s390_init(MachineState *machine)
 
     /* Create VirtIO network adapters */
     s390_create_virtio_net((BusState *)s390_bus, "virtio-net-s390");
+
+    /* Register savevm handler for guest TOD clock */
+    register_savevm(NULL, "todclock", 0, 1, gtod_save, gtod_load, NULL);
 }
 
 void s390_nmi(NMIState *n, int cpu_index, Error **errp)