virtio-mem: generalize check for added memory

Let's check by traversing busy system RAM resources instead, to avoid
relying on memory block states.

Don't use walk_system_ram_range(), as that works on pages and we want to
use the bare addresses we have easily at hand.

This is a preparation for Big Block Mode (BBM), which won't have memory
block states.
Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20201112133815.13332-12-david@redhat.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/virtio/virtio_mem.c

@@ -1833,6 +1833,20 @@ static void virtio_mem_delete_resource(struct virtio_mem *vm)
 	vm->parent_resource = NULL;
 }
 
+static int virtio_mem_range_has_system_ram(struct resource *res, void *arg)
+{
+	return 1;
+}
+
+static bool virtio_mem_has_memory_added(struct virtio_mem *vm)
+{
+	const unsigned long flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
+
+	return walk_iomem_res_desc(IORES_DESC_NONE, flags, vm->addr,
+				   vm->addr + vm->region_size, NULL,
+				   virtio_mem_range_has_system_ram) == 1;
+}
+
 static int virtio_mem_probe(struct virtio_device *vdev)
 {
 	struct virtio_mem *vm;
@@ -1954,10 +1968,7 @@ static void virtio_mem_remove(struct virtio_device *vdev)
 	 * the system. And there is no way to stop the driver/device from going
 	 * away. Warn at least.
 	 */
-	if (vm->nb_mb_state[VIRTIO_MEM_MB_STATE_OFFLINE] ||
-	    vm->nb_mb_state[VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL] ||
-	    vm->nb_mb_state[VIRTIO_MEM_MB_STATE_ONLINE] ||
-	    vm->nb_mb_state[VIRTIO_MEM_MB_STATE_ONLINE_PARTIAL]) {
+	if (virtio_mem_has_memory_added(vm)) {
 		dev_warn(&vdev->dev, "device still has system memory added\n");
 	} else {
 		virtio_mem_delete_resource(vm);