I am trying to passthrough R9 Nano to a VM, and facing some problems. After
Windows 7 has been installed, the latest AMD Crimson edition driver is
installed. At first time, the driver works properly. There appears to have the
problem when I power off the vm and restart it. The driver was not working
until I reboot the host.

Here is my system.

Manufacturer: Supermicro
Product Name: X10DAi
CPU: Intel(R) Xeon(R) CPU E5-2620 v3 @ 2.40GHz
memory: 8GB 
linux kernel: 3.19.0

$ cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-3.19.0 root=UUID=fc28306a-e168-406a-805d-cadf70de53ec
ro quiet splash intel-iommu=on vfio_iommu_type1.allow_unsafe_interrupts=1
vt.handoff=7

I tried to use qemu version 2.3.1, 2.4.1, and 2.5.1. 
I also added the device id number into the function vfio_setup_resetfn(), but
the problem remains.

I start my virtual machine with the following code.

qemu-system-x86_64 -enable-kvm \
-M pc -m 4096 -cpu host \
-smp 4,sockets=1,cores=4,threads=1 \
-rtc base=localtime \
-vnc :0 \
-vga none \
-device lsi,id=scsi0,bus=pci.0 \
-device vfio-pci,host=03:00.0,x-vga=on \
-device vfio-pci,host=03:00.1 \
-hda $1 \
-monitor stdio