How to allow guest to write on 9p/virtfs shared folder?

[Manuel Reimer <Manuel.Spam@nurfuerspam.de>]

Hello,

today, I upgraded my kernel and I seem to have gotten a new kvm backend 
with this.

Now my guest systems are no longer able to write to the host filesystem.

I share the filesystem using the following command to qemu:

-virtfs 
local,id=fsdev0,path=$SHARED,security_model=passthrough,mount_tag=vmshared

and on guest side (fstab):

vmshared /mnt/vmshared 9p 
rw,comment=systemd.automount,trans=virtio,access=any 0 0

Versions:

$ uname -a
Linux manuelspc 3.11.1-1-ARCH #1 SMP PREEMPT Sat Sep 14 19:30:21 CEST 
2013 x86_64 GNU/Linux
$ qemu-system-x86_64 --version
QEMU emulator version 1.5.2, Copyright (c) 2003-2008 Fabrice Bellard

Can someone please help me to get back my writing permissions?

Thank you in advance

Yours

Manuel