Hi Marc,
Thank you for your reply.
在 2022/7/12 23:25, Marc Zyngier 写道:
Hi Xiang,
On Tue, 12 Jul 2022 13:55:16 +0100,
"chenxiang (M)" <chenxiang66@xxxxxxxxxxxxx> wrote:
Hi,
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?
I have a hunch: QEMU cannot know that the guest is only using 3 MSIs
out of the 4 that the device can use, and PCI/Multi-MSI only has a
single enable bit for all MSIs. So it probably iterates over all
possible MSIs and enable the forwarding. Since the guest has only
created 3 mappings in the virtual ITS, the last call fails. I would
expect the guest to still work properly though.
Yes, that's the reason of exception print.
Is it possible for QEMU to get the exact number of interrupts guest is
using? It seems not.
Thanks,
M.
