I use pci passthrough.Unfortunately my card is sharing the same irq of an usb controller.I use this procedure:Find the sharing irq, in my case return 21    lspci -s 00:05:00 -vvvFind the irqcat /proc/interrupts|grep 21:Return me usb2So search usb2find  /sys/devices/pci0000\:00/0000\:00\:* -iname usb2Return me pci address, so I go to addressand remove the usb2 hub-slotcd /sys/devices/pci0000\:00/0000\:00\:13.2/echo -n 1 > removeThe question is: how to read the usb2 slot?If you have a question like: why do you remove the slot?The answer is: my pci card is really old(1999!) and doesn't sharethe irq, so if you run a vm with this card the interrupt must be unique,otherwise qemu/libvirt gives an error.
Is possible to re-add a removed iommu device?
pci passthrough;iommu