The backend does not reset them until the vdpa file descriptor is closed
so there is no harm in doing it only once.

This allows the destination of a live migration to premap memory in
batches, using VHOST_BACKEND_F_IOTLB_BATCH.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-vdpa.c | 50 ++++++++++++++++--------------------------
 1 file changed, 19 insertions(+), 31 deletions(-)

diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
index 449c3794b2..43f7c382b1 100644
--- a/hw/virtio/vhost-vdpa.c
+++ b/hw/virtio/vhost-vdpa.c
@@ -587,11 +587,25 @@ static int vhost_vdpa_init(struct vhost_dev *dev, void *opaque, Error **errp)
     struct vhost_vdpa *v = opaque;
     assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_VDPA);
     trace_vhost_vdpa_init(dev, v->shared, opaque);
+    uint64_t backend_features;
+    uint64_t qemu_backend_features = 0x1ULL << VHOST_BACKEND_F_IOTLB_MSG_V2 |
+                                     0x1ULL << VHOST_BACKEND_F_IOTLB_BATCH |
+                                     0x1ULL << VHOST_BACKEND_F_IOTLB_ASID |
+                                     0x1ULL << VHOST_BACKEND_F_SUSPEND;
     int ret;
 
     v->dev = dev;
     dev->opaque =  opaque ;
     v->shared->listener = vhost_vdpa_memory_listener;
+
+    if (vhost_vdpa_call(dev, VHOST_GET_BACKEND_FEATURES, &backend_features)) {
+        return -EFAULT;
+    }
+
+    backend_features &= qemu_backend_features;
+
+    dev->backend_cap = backend_features;
+    v->shared->backend_cap = backend_features;
     vhost_vdpa_init_svq(dev, v);
 
     error_propagate(&dev->migration_blocker, v->migration_blocker);
@@ -599,6 +613,11 @@ static int vhost_vdpa_init(struct vhost_dev *dev, void *opaque, Error **errp)
         return 0;
     }
 
+    ret = vhost_vdpa_call(dev, VHOST_SET_BACKEND_FEATURES, &backend_features);
+    if (ret) {
+        return -EFAULT;
+    }
+
     /*
      * If dev->shadow_vqs_enabled at initialization that means the device has
      * been started with x-svq=on, so don't block migration
@@ -829,36 +848,6 @@ static int vhost_vdpa_set_features(struct vhost_dev *dev,
     return vhost_vdpa_add_status(dev, VIRTIO_CONFIG_S_FEATURES_OK);
 }
 
-static int vhost_vdpa_set_backend_cap(struct vhost_dev *dev)
-{
-    struct vhost_vdpa *v = dev->opaque;
-
-    uint64_t features;
-    uint64_t f = 0x1ULL << VHOST_BACKEND_F_IOTLB_MSG_V2 |
-        0x1ULL << VHOST_BACKEND_F_IOTLB_BATCH |
-        0x1ULL << VHOST_BACKEND_F_IOTLB_ASID |
-        0x1ULL << VHOST_BACKEND_F_SUSPEND;
-    int r;
-
-    if (vhost_vdpa_call(dev, VHOST_GET_BACKEND_FEATURES, &features)) {
-        return -EFAULT;
-    }
-
-    features &= f;
-
-    if (vhost_vdpa_first_dev(dev)) {
-        r = vhost_vdpa_call(dev, VHOST_SET_BACKEND_FEATURES, &features);
-        if (r) {
-            return -EFAULT;
-        }
-    }
-
-    dev->backend_cap = features;
-    v->shared->backend_cap = features;
-
-    return 0;
-}
-
 static int vhost_vdpa_get_device_id(struct vhost_dev *dev,
                                     uint32_t *device_id)
 {
@@ -1512,7 +1501,6 @@ const VhostOps vdpa_ops = {
         .vhost_set_vring_kick = vhost_vdpa_set_vring_kick,
         .vhost_set_vring_call = vhost_vdpa_set_vring_call,
         .vhost_get_features = vhost_vdpa_get_features,
-        .vhost_set_backend_cap = vhost_vdpa_set_backend_cap,
         .vhost_set_owner = vhost_vdpa_set_owner,
         .vhost_set_vring_endian = NULL,
         .vhost_backend_memslots_limit = vhost_vdpa_memslots_limit,
-- 
2.39.3