Description of problem:
when i boot a guest(rhel6.4) with rng device, open the hwrng device in guest ,can not fetch the data form host. in guest the virtio-rng driver have loaded , the hwrng is available and using by kernel.

Version-Release number of selected component (if applicable):
kernel: kernel-3.7.0-0.34.el7.x86_64
qemu: qemu-kvm-1.3.0-5.el7.x86_64

How reproducible:
100%

Steps to Reproduce:
1.[Host] boot guest with rng device like :
   -device virtio-rng-pci
2.[guest] check the driver virtio-rng have been loaded.
   #lsmod | grep rng
3.[guest] check the rng device in availble in guest
   $ cat /sys/devices/virtual/misc/hw_random/rng_available
4.[guest] Check is the current hwrng device in use by the kernel:
   $ cat /sys/devices/virtual/misc/hw_random/rng_current
5.[guest] Open rng device to fetch data from host (wait several minutes, do some op in host, like move the mice).
   #cat /dev/hwrng
 
 
Actual results:
   in step 2 ,3 ,4 we can see the drive have been loaded. the hwrng device is available and is using by the kernel. but in step5 "cat /dev/hwrng" have no output. 

Expected results:
 in step 5 should have some output.

Additional info:
qemu-command:
/usr/libexec/qemu-kvm \
-name 'vm1' \
-nodefaults \
-m 4096 \
-smp 4,cores=2,threads=1,sockets=2 \
-vnc :22 \
-vga qxl \
-rtc base=utc,clock=host,driftfix=none \
-drive file=/root/RHEL-Server-6.4-64-virtio.qcow2,if=none,cache=none,id=virtio0 \
-device virtio-blk-pci,drive=virtio0 \
-device virtio-net-pci,netdev=id3Ibo2c,mac=9a:5e:5f:60:61:62 \
-netdev tap,id=id3Ibo2c,script=/root/qemu-ifup-switch \
-device ich9-usb-uhci1,id=usb1 \
-boot order=cdn,once=c,menu=on \
-enable-kvm \
-monitor stdio \
-global PIIX4_PM.disable_s3=0 \
-global PIIX4_PM.disable_s4=0 \
-chardev socket,id=qmp_id_qmpmonitor1,path=/tmp/qmpmonitor-1,server,nowait \
-mon chardev=qmp_id_qmpmonitor1,mode=control \
-chardev socket,id=isa-serial-1,path=/tmp/isa-serial-1,server,nowait \
-device isa-serial,chardev=isa-serial-1 \
-device virtio-serial,id=virt-serial-1,max_ports=31,bus=pci.0 \
-chardev socket,id=virtio-serial-1-1,path=/tmp/virtio-serial-1-1,server,nowait \
-device virtserialport,chardev=virtio-serial-1-1,name=virtio.serial.1.1,bus=virt-serial-1.0,id=virtio-serial-port1-1 \
-device virtio-serial,id=virt-console-1 \
-chardev socket,id=virtio-console-1-1,path=/tmp/virtio-console-1-1,server,nowait \
-device virtconsole,chardev=virtio-console-1-1,name=virtio.console.1.1,bus=virt-console-1.0 \
-device virtio-rng-pci

host cpuinfo:
Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                8
On-line CPU(s) list:   0-7
Thread(s) per core:    2
Core(s) per socket:    4
Socket(s):             1
NUMA node(s):          1
Vendor ID:             GenuineIntel
CPU family:            6
Model:                 42
Stepping:              7
CPU MHz:               1600.000
BogoMIPS:              6784.61
Virtualization:        VT-x
L1d cache:             32K
L1i cache:             32K
L2 cache:              256K
L3 cache:              8192K
NUMA node0 CPU(s):     0-7