There is a bug reported against hyperv-daemons:
https://bugzilla.redhat.com/show_bug.cgi?id=1577692

which may also require us to do z-stream. There is an upstream commit
fixing the issue:

commit ea81fdf0981d9a4a998a015d325bed67624811f7
Author: Alex Ng <alexng.com>
Date:   Sun Aug 6 13:12:52 2017 -0700

    Tools: hv: vss: Skip freezing filesystems backed by loop

(which has its own issues, I'm going to address these upstream).

Anyway, with this commit included hypervvssd tries to do stat() on all block devices in /dev/ and SELinux blocks it:

time->Tue May 22 18:42:07 2018
type=SYSCALL msg=audit(1526985727.990:120): arch=c000003e syscall=4 success=no exit=-13 a0=7fb2ee1ff250 a1=7ffe3c08a7f0 a2=7ffe3c08a7f0 a3=4000 items=0 ppid=1 pid=647 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=(none) ses=4294967295 comm="hypervvssd" exe="/usr/sbin/hypervvssd" subj=system_u:system_r:hypervvssd_t:s0 key=(null)
type=AVC msg=audit(1526985727.990:120): avc:  denied  { getattr } for  pid=647 comm="hypervvssd" path="/dev/dm-0" dev="devtmpfs" ino=9137 scontext=system_u:system_r:hypervvssd_t:s0 tcontext=system_u:object_r:fixed_disk_device_t:s0 tclass=blk_file

We need to get this fixed at least for 7.6 where the hypervvssd commit in question is already present and prepare for z-stream update in case the request will be granted.

audit2allow produces the following output:
allow hypervvssd_t fixed_disk_device_t:blk_file getattr;

but I'm not sure about fixed_disk_device_t as we probably want all block devices.