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 -vvv

Find the irq

cat /proc/interrupts|grep 21:

Return me usb2

So search usb2

find  /sys/devices/pci0000\:00/0000\:00\:* -iname usb2

Return me pci address, so I go to address and remove the usb2 hub-slot

cd /sys/devices/pci0000\:00/0000\:00\:13.2/
echo -n 1 > remove

The 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 share the irq, so if you run a vm with this card the interrupt must be unique, otherwise qemu/libvirt gives an error.

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