Comment 5 for bug 1875139

This was indeed caused by libvirt starting to use -blockdev. The issue is that qemu's 'auto-read-only' property which is used by libvirt for the backing files doesn't properly work if the 'host_device' backend encounters a read-only LV.

The above situation also happens if you have an read-only LV in the backing chain.

In the current upstream situation of qemu's APIs there currently isn't anything that libvirt can do in this case, because any solution would either not fix the problem completely or would require sacrificing other features, the auto-read-only property needs to be fixed in qemu.

I've also filed https://bugzilla.redhat.com/show_bug.cgi?id=1828252 to track this issue.