vdpa: move backend_cap to vhost_vdpa_shared

Next patches will register the vhost_vdpa memory listener while the VM
is migrating at the destination, so we can map the memory to the device
before stopping the VM at the source.  The main goal is to reduce the
downtime.

However, the destination QEMU is unaware of which vhost_vdpa device will
register its memory_listener.  If the source guest has CVQ enabled, it
will be the CVQ device.  Otherwise, it  will be the first one.

Move the backend_cap member to VhostVDPAShared so all vhost_vdpa can use
it, rather than always in the first / last vhost_vdpa.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20231221174322.3130442-9-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>

hw/virtio/vhost-vdpa.c

@@ -161,7 +161,7 @@ static void vhost_vdpa_listener_begin_batch(struct vhost_vdpa *v)
 
 static void vhost_vdpa_iotlb_batch_begin_once(struct vhost_vdpa *v)
 {
-    if (v->dev->backend_cap & (0x1ULL << VHOST_BACKEND_F_IOTLB_BATCH) &&
+    if (v->shared->backend_cap & (0x1ULL << VHOST_BACKEND_F_IOTLB_BATCH) &&
         !v->shared->iotlb_batch_begin_sent) {
         vhost_vdpa_listener_begin_batch(v);
     }
@@ -172,11 +172,10 @@ static void vhost_vdpa_iotlb_batch_begin_once(struct vhost_vdpa *v)
 static void vhost_vdpa_listener_commit(MemoryListener *listener)
 {
     struct vhost_vdpa *v = container_of(listener, struct vhost_vdpa, listener);
-    struct vhost_dev *dev = v->dev;
     struct vhost_msg_v2 msg = {};
     int fd = v->shared->device_fd;
 
-    if (!(dev->backend_cap & (0x1ULL << VHOST_BACKEND_F_IOTLB_BATCH))) {
+    if (!(v->shared->backend_cap & (0x1ULL << VHOST_BACKEND_F_IOTLB_BATCH))) {
         return;
     }
 
@@ -838,6 +837,8 @@ static int vhost_vdpa_set_features(struct vhost_dev *dev,
 
 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 |
@@ -859,6 +860,7 @@ static int vhost_vdpa_set_backend_cap(struct vhost_dev *dev)
     }
 
     dev->backend_cap = features;
+    v->shared->backend_cap = features;
 
     return 0;
 }

include/hw/virtio/vhost-vdpa.h

@@ -38,6 +38,9 @@ typedef struct vhost_vdpa_shared {
     /* IOVA mapping used by the Shadow Virtqueue */
     VhostIOVATree *iova_tree;
 
+    /* Copy of backend features */
+    uint64_t backend_cap;
+
     bool iotlb_batch_begin_sent;
 
     /* Vdpa must send shadow addresses as IOTLB key for data queues, not GPA */