[PATCH v4 09/15] vdpa: add vdpa net migration state notifier

["Eugenio Pérez" <eperezma@redhat.com>]

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

Ideally, these changes should not be net specific. 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).

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.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
v4:
* Delete duplication of set shadow_data and shadow_vqs_enabled moving it
  to data / cvq net start functions.

v3:
* Check for migration state at vdpa device start to enable SVQ in data
  vqs.

v1 from RFC:
* Add TODO to use the resume operation in the future.
* Use migration_in_setup and migration_has_failed instead of a
  complicated switch case.
---
 net/vhost-vdpa.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 69 insertions(+), 3 deletions(-)

diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
index b89c99066a..c5512ddf10 100644
--- a/net/vhost-vdpa.c
+++ b/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 @@ out:
         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;
-- 
2.31.1