KVM guest cannot write to 9p share owned by non-root
I had similar problems and never got it working with 9p, and as other commenters have said 9p is not mature.
I ended up using samba to mount a host filesystem and it's working fine. Any other network filesystem would do the job, too, probably (e.g. NFS, which is recommended by Red Hat; see link from @Diagon's comment https://access.redhat.com/discussions/1119043).