# dd if=/dev/zero of=loopbackfile1.img bs=500M count=1
1+0 records in
1+0 records out
524288000 bytes (524 MB, 500 MiB) copied, 2.32777 s, 225 MB/s

# dd if=/dev/zero of=loopbackfile2.img bs=500M count=1
1+0 records in
1+0 records out
524288000 bytes (524 MB, 500 MiB) copied, 1.89992 s, 276 MB/s

# losetup -fP /root/loopbackfile1.img

# losetup -fP /root/loopbackfile2.img

# losetup -l
NAME       SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE               DIO LOG-SEC
/dev/loop1         0      0         0  0 /root/loopbackfile2.img   0     512
/dev/loop0         0      0         0  0 /root/loopbackfile1.img   0     512

# pvcreate /dev/loop0
  Physical volume "/dev/loop0" successfully created.

# vgcreate LOOP_VG /dev/loop0
  Volume group "LOOP_VG" successfully created

# lvcreate -L 300MB LOOP_VG -n LV /dev/loop0
  Logical volume "LV" created.

# mkfs.ext4 /dev/mapper/LOOP_VG-LV
mke2fs 1.44.1 (24-Mar-2018)
Discarding device blocks: done
Creating filesystem with 307200 1k blocks and 76912 inodes
Filesystem UUID: 344289a3-e251-4d88-b03d-a71a4be2a8ec
Superblock backups stored on blocks:
        8193, 24577, 40961, 57345, 73729, 204801, 221185

Allocating group tables: done
Writing inode tables: done
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: done

# mount /dev/mapper/LOOP_VG-LV /mnt

# mount|grep LOOP
/dev/mapper/LOOP_VG-LV on /mnt type ext4 (rw,relatime)

# cryptsetup luksFormat --type luks2 --sector-size 4096 /dev/loop1

WARNING!
========
This will overwrite data on /dev/loop1 irrevocably.

Are you sure? (Type uppercase yes): YES
Enter passphrase for /dev/loop1: loop
Verify passphrase: loop
<< cmd takes some seconds >>

# cryptsetup luksOpen /dev/loop1 enc-loop
Enter passphrase for /dev/loop1: loop

# pvcreate /dev/mapper/enc-loop
  Physical volume "/dev/mapper/enc-loop" successfully created.

# vgextend LOOP_VG /dev/mapper/enc-loop
  Volume group "LOOP_VG" successfully extended

# pvs
  PV                   VG      Fmt  Attr PSize   PFree
  /dev/loop0           LOOP_VG lvm2 a--  496.00m 196.00m
  /dev/mapper/enc-loop LOOP_VG lvm2 a--  492.00m 492.00m

# pvmove -dddddd /dev/loop0 /dev/mapper/enc-loop
  /dev/loop0: Moved: 30.67%
  /dev/loop0: Moved: 100.00%

# pvs
  /dev/LOOP_VG/LV: read failed after 0 of 1024 at 0: Invalid argument
  /dev/LOOP_VG/LV: read failed after 0 of 1024 at 314507264: Invalid argument
  /dev/LOOP_VG/LV: read failed after 0 of 1024 at 314564608: Invalid argument
  /dev/LOOP_VG/LV: read failed after 0 of 1024 at 4096: Invalid argument
  PV                   VG      Fmt  Attr PSize   PFree
  /dev/loop0           LOOP_VG lvm2 a--  496.00m 496.00m
  /dev/mapper/enc-loop LOOP_VG lvm2 a--  492.00m 192.00m