make qemu work with cx5 passthrough in centos
1. In BIOS, enable IOMMU. Security->Virtualization->VT-d
2. In kernel options, enable IOMMU. Verify INTEL_IOMMU=y
3. In kernel command line, append intel_iommu=on.
4. modprobe -v vfio && modprobe -v vfio-pci
5. echo 0000:3b:00.0 > /sys/bus/pci/devices/0000:3b:00.0/driver/unbind
6. lspci -ns 0000:3b:00.0
3b:00.0 0200: 15b3:a2d6
7.echo 15b3 a2d6 > /sys/bus/pci/drivers/vfio-pci/new_id
8. qemu-system-x86_64 -m 4096 -smp 4 --enable-kvm \
-drive file=debian99.img \
-device vfio-pci,host=0000:3b:00.0