KVM host, add LV to guest

I don't think there is a way to skip having LVM running in the guest and just do lvextend on the host and then resize2fs in the guest?

There is absolutely no need to use LVM inside the guest. You can use block devices directly. Using LVM inside the guest gives you almost nothing (since you're already using LVM on the host to manage space).

If you mean "libvirt" by "KVM", virsh blockresizeafter resizing the block device , you can use the command to make the guest recognize the extra space. That is, if I have a visitor with an additional LV:

</disk><disk type="block" device="disk">
  <driver name="qemu" type="raw"/>
  <source dev="/dev/tank/foobar"/>
  <backingStore/>
  <target dev="vdb" bus="virtio"/>
  <alias name="virtio-disk1"/></disk>

Where:

# lvs
  foobar                                      tank           -wi-ao----   4.00g                                                              

I can add space on the LV on the host:

# lvresize -L +2G /dev/tank/foobar

Tell libvirt to update the size:

# virsh blockresize myguest /dev/tank/foobar --size 0

Then inside the guest, resize the file:

guest# resize2fs 1.42.12 (29-Aug-2014)
Resizing the filesystem on /dev/vdb to 1572864 (4k) blocks.
The filesystem on /dev/vdb is now 1572864 (4k) blocks long.