vdpa: add vdpa net migration state notifier

This allows net to restart the device backend to configure SVQ on it.

Ideally, these changes should not be net specific and they could be done
in:
* vhost_vdpa_set_features (with VHOST_F_LOG_ALL)
* vhost_vdpa_set_vring_addr (with .enable_log)
* vhost_vdpa_set_log_base.

However, the vdpa net backend is the one with enough knowledge to
configure everything because of some reasons:
* Queues might need to be shadowed or not depending on its kind (control
  vs data).
* Queues need to share the same map translations (iova tree).

Also, there are other problems that may have solutions but complicates
the implementation at this stage:
* We're basically duplicating vhost_dev_start and vhost_dev_stop, and
  they could go out of sync.  If we want to reuse them, we need a way to
  skip some function calls to avoid recursiveness (either vhost_ops ->
  vhost_set_features, vhost_set_vring_addr, ...).
* We need to traverse all vhost_dev of a given net device twice: one to
  stop and get the vq state and another one after the reset to
  configure properties like address, fd, etc.

Because of that it is cleaner to restart the whole net backend and
configure again as expected, similar to how vhost-kernel moves between
userspace and passthrough.

If more kinds of devices need dynamic switching to SVQ we can:
* Create a callback struct like VhostOps and move most of the code
  there.  VhostOps cannot be reused since all vdpa backend share them,
  and to personalize just for networking would be too heavy.
* Add a parent struct or link all the vhost_vdpa or vhost_dev structs so
  we can traverse them.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Message-Id: <20230303172445.1089785-9-eperezma@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

net/vhost-vdpa.c

@@ -26,12 +26,15 @@
 #include <err.h>
 #include "standard-headers/linux/virtio_net.h"
 #include "monitor/monitor.h"
+#include "migration/migration.h"
+#include "migration/misc.h"
 #include "hw/virtio/vhost.h"
 
 /* Todo:need to add the multiqueue support here */
 typedef struct VhostVDPAState {
     NetClientState nc;
     struct vhost_vdpa vhost_vdpa;
+    Notifier migration_state;
     VHostNetState *vhost_net;
 
     /* Control commands shadow buffers */
@@ -239,10 +242,59 @@ static VhostVDPAState *vhost_vdpa_net_first_nc_vdpa(VhostVDPAState *s)
     return DO_UPCAST(VhostVDPAState, nc, nc0);
 }
 
+static void vhost_vdpa_net_log_global_enable(VhostVDPAState *s, bool enable)
+{
+    struct vhost_vdpa *v = &s->vhost_vdpa;
+    VirtIONet *n;
+    VirtIODevice *vdev;
+    int data_queue_pairs, cvq, r;
+
+    /* We are only called on the first data vqs and only if x-svq is not set */
+    if (s->vhost_vdpa.shadow_vqs_enabled == enable) {
+        return;
+    }
+
+    vdev = v->dev->vdev;
+    n = VIRTIO_NET(vdev);
+    if (!n->vhost_started) {
+        return;
+    }
+
+    data_queue_pairs = n->multiqueue ? n->max_queue_pairs : 1;
+    cvq = virtio_vdev_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ) ?
+                                  n->max_ncs - n->max_queue_pairs : 0;
+    /*
+     * TODO: vhost_net_stop does suspend, get_base and reset. We can be smarter
+     * in the future and resume the device if read-only operations between
+     * suspend and reset goes wrong.
+     */
+    vhost_net_stop(vdev, n->nic->ncs, data_queue_pairs, cvq);
+
+    /* Start will check migration setup_or_active to configure or not SVQ */
+    r = vhost_net_start(vdev, n->nic->ncs, data_queue_pairs, cvq);
+    if (unlikely(r < 0)) {
+        error_report("unable to start vhost net: %s(%d)", g_strerror(-r), -r);
+    }
+}
+
+static void vdpa_net_migration_state_notifier(Notifier *notifier, void *data)
+{
+    MigrationState *migration = data;
+    VhostVDPAState *s = container_of(notifier, VhostVDPAState,
+                                     migration_state);
+
+    if (migration_in_setup(migration)) {
+        vhost_vdpa_net_log_global_enable(s, true);
+    } else if (migration_has_failed(migration)) {
+        vhost_vdpa_net_log_global_enable(s, false);
+    }
+}
+
 static void vhost_vdpa_net_data_start_first(VhostVDPAState *s)
 {
     struct vhost_vdpa *v = &s->vhost_vdpa;
 
+    add_migration_state_change_notifier(&s->migration_state);
     if (v->shadow_vqs_enabled) {
         v->iova_tree = vhost_iova_tree_new(v->iova_range.first,
                                            v->iova_range.last);
@@ -256,6 +308,15 @@ static int vhost_vdpa_net_data_start(NetClientState *nc)
 
     assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_VDPA);
 
+    if (s->always_svq ||
+        migration_is_setup_or_active(migrate_get_current()->state)) {
+        v->shadow_vqs_enabled = true;
+        v->shadow_data = true;
+    } else {
+        v->shadow_vqs_enabled = false;
+        v->shadow_data = false;
+    }
+
     if (v->index == 0) {
         vhost_vdpa_net_data_start_first(s);
         return 0;
@@ -276,6 +337,10 @@ static void vhost_vdpa_net_client_stop(NetClientState *nc)
 
     assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_VDPA);
 
+    if (s->vhost_vdpa.index == 0) {
+        remove_migration_state_change_notifier(&s->migration_state);
+    }
+
     dev = s->vhost_vdpa.dev;
     if (dev->vq_index + dev->nvqs == dev->vq_index_end) {
         g_clear_pointer(&s->vhost_vdpa.iova_tree, vhost_iova_tree_delete);
@@ -412,11 +477,12 @@ static int vhost_vdpa_net_cvq_start(NetClientState *nc)
     s = DO_UPCAST(VhostVDPAState, nc, nc);
     v = &s->vhost_vdpa;
 
-    v->shadow_data = s->always_svq;
+    s0 = vhost_vdpa_net_first_nc_vdpa(s);
+    v->shadow_data = s0->vhost_vdpa.shadow_vqs_enabled;
     v->shadow_vqs_enabled = s->always_svq;
     s->vhost_vdpa.address_space_id = VHOST_VDPA_GUEST_PA_ASID;
 
-    if (s->always_svq) {
+    if (s->vhost_vdpa.shadow_data) {
         /* SVQ is already configured for all virtqueues */
         goto out;
     }
@@ -473,7 +539,6 @@ static int vhost_vdpa_net_cvq_start(NetClientState *nc)
         return 0;
     }
 
-    s0 = vhost_vdpa_net_first_nc_vdpa(s);
     if (s0->vhost_vdpa.iova_tree) {
         /*
          * SVQ is already configured for all virtqueues.  Reuse IOVA tree for
@@ -749,6 +814,7 @@ static NetClientState *net_vhost_vdpa_init(NetClientState *peer,
     s->vhost_vdpa.device_fd = vdpa_device_fd;
     s->vhost_vdpa.index = queue_pair_index;
     s->always_svq = svq;
+    s->migration_state.notify = vdpa_net_migration_state_notifier;
     s->vhost_vdpa.shadow_vqs_enabled = svq;
     s->vhost_vdpa.iova_range = iova_range;
     s->vhost_vdpa.shadow_data = svq;