Red Hat KVM PCI passthrough

for Intel system:

1. enable Intel VT-d in BIOS

2. add intel_iommu=on to the kernel line in /boot/grub/grub.conf

3. reboot

4. add PCI device to VM in virt manager

for AMD system:

1. enable AMD IOMMU in BIOS

2. add amd_iommu=on to the kernel line in /boot/grub/grub.conf

3. reboot

4. add PCI device to VM in virt manager