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Re: [PATCH v13 4/7] s390x/cpu_topology: CPU topology migration


From: Christian Borntraeger
Subject: Re: [PATCH v13 4/7] s390x/cpu_topology: CPU topology migration
Date: Tue, 13 Dec 2022 14:26:08 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.0

Am 08.12.22 um 10:44 schrieb Pierre Morel:
The migration can only take place if both source and destination
of the migration both use or both do not use the CPU topology
facility.

We indicate a change in topology during migration postload for the
case the topology changed between source and destination.

I dont get why we need this? If the target QEMU has topology it should
already create this according to the configuration. WHy do we need a
trigger?


Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
---
  target/s390x/cpu.h        |  1 +
  hw/s390x/cpu-topology.c   | 49 +++++++++++++++++++++++++++++++++++++++
  target/s390x/cpu-sysemu.c |  8 +++++++
  3 files changed, 58 insertions(+)

diff --git a/target/s390x/cpu.h b/target/s390x/cpu.h
index bc1a7de932..284c708a6c 100644
--- a/target/s390x/cpu.h
+++ b/target/s390x/cpu.h
@@ -854,6 +854,7 @@ void s390_do_cpu_set_diag318(CPUState *cs, run_on_cpu_data 
arg);
  int s390_assign_subch_ioeventfd(EventNotifier *notifier, uint32_t sch_id,
                                  int vq, bool assign);
  void s390_cpu_topology_reset(void);
+int s390_cpu_topology_mtcr_set(void);
  #ifndef CONFIG_USER_ONLY
  unsigned int s390_cpu_set_state(uint8_t cpu_state, S390CPU *cpu);
  #else
diff --git a/hw/s390x/cpu-topology.c b/hw/s390x/cpu-topology.c
index f54afcf550..8a2fe041d4 100644
--- a/hw/s390x/cpu-topology.c
+++ b/hw/s390x/cpu-topology.c
@@ -18,6 +18,7 @@
  #include "target/s390x/cpu.h"
  #include "hw/s390x/s390-virtio-ccw.h"
  #include "hw/s390x/cpu-topology.h"
+#include "migration/vmstate.h"
/**
   * s390_has_topology
@@ -129,6 +130,53 @@ static void s390_topology_reset(DeviceState *dev)
      s390_cpu_topology_reset();
  }
+/**
+ * cpu_topology_postload
+ * @opaque: a pointer to the S390Topology
+ * @version_id: version identifier
+ *
+ * We check that the topology is used or is not used
+ * on both side identically.
+ *
+ * If the topology is in use we set the Modified Topology Change Report
+ * on the destination host.
+ */
+static int cpu_topology_postload(void *opaque, int version_id)
+{
+    int ret;
+
+    /* We do not support CPU Topology, all is good */
+    if (!s390_has_topology()) {
+        return 0;
+    }
+
+    /* We support CPU Topology, set the MTCR unconditionally */
+    ret = s390_cpu_topology_mtcr_set();
+    if (ret) {
+        error_report("Failed to set MTCR: %s", strerror(-ret));
+    }
+    return ret;
+}
+
+/**
+ * cpu_topology_needed:
+ * @opaque: The pointer to the S390Topology
+ *
+ * We always need to know if source and destination use the topology.
+ */
+static bool cpu_topology_needed(void *opaque)
+{
+    return s390_has_topology();
+}
+
+const VMStateDescription vmstate_cpu_topology = {
+    .name = "cpu_topology",
+    .version_id = 1,
+    .post_load = cpu_topology_postload,
+    .minimum_version_id = 1,
+    .needed = cpu_topology_needed,
+};
+
  /**
   * topology_class_init:
   * @oc: Object class
@@ -145,6 +193,7 @@ static void topology_class_init(ObjectClass *oc, void *data)
      device_class_set_props(dc, s390_topology_properties);
      set_bit(DEVICE_CATEGORY_MISC, dc->categories);
      dc->reset = s390_topology_reset;
+    dc->vmsd = &vmstate_cpu_topology;
  }
static const TypeInfo cpu_topology_info = {
diff --git a/target/s390x/cpu-sysemu.c b/target/s390x/cpu-sysemu.c
index e27864c5f5..a8e3e6219d 100644
--- a/target/s390x/cpu-sysemu.c
+++ b/target/s390x/cpu-sysemu.c
@@ -319,3 +319,11 @@ void s390_cpu_topology_reset(void)
          }
      }
  }
+
+int s390_cpu_topology_mtcr_set(void)
+{
+    if (kvm_enabled()) {
+        return kvm_s390_topology_set_mtcr(1);
+    }
+    return -ENOENT;
+}



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