[QUESTION] Exception print when enabling GICv4

From: chenxiang (M)
Date: Tue Jul 12 2022 - 08:55:26 EST

I encounter a issue related to GICv4 enable on ARM64 platform (kernel 5.19-rc4, qemu 6.2.0):
We have a accelaration module whose VF has 3 MSI interrupts, and we passthrough it to virtual machine with following steps:

echo 0000:79:00.1 > /sys/bus/pci/drivers/hisi_hpre/unbind
echo vfio-pci > /sys/devices/pci0000\:78/0000\:78\:00.0/0000\:79\:00.1/driver_override
echo 0000:79:00.1 > /sys/bus/pci/drivers_probe

Then we boot VM with "-device vfio-pci,host=79:00.1,id=net0 \".
When insmod the driver which registers 3 PCI MSI interrupts in VM, some exception print occur as following:

vfio-pci 0000:3a:00.1: irq bypass producer (token 000000008f08224d) registration fails: 66311

I find that bit[6:4] of register PCI_MSI_FLAGS is 2 (4 MSI interrupts) though we only register 3 PCI MSI interrupt,

and only 3 MSI interrupt is activated at last.
It allocates 4 vectors in function vfio_msi_enable() (qemu) as it reads the register PCI_MSI_FLAGS.
Later it will call system call VFIO_DEVICE_SET_IRQS to set forwarding for those interrupts
using function kvm_vgic_v4_set_forrwarding() as GICv4 is enabled. For interrupt 0~2, it success to set forwarding as they are already activated,
but for the 4th interrupt, it is not activated, so ite is not found in function vgic_its_resolve_lpi(), so above printk occurs.

It seems that we only allocate and activate 3 MSI interrupts in guest while it tried to set forwarding for 4 MSI interrupts in host.
Do you have any idea about this issue?

Best regards,

Xiang Chen