Re: [Qemu-devel] Question about the vfio device interrupt

[Auger Eric]

Hi,

On 5/15/19 12:01 PM, Li Qiang wrote:
> Hello Paolo, Alex and all,
> 
> In vfio_intx_enable_kvm(qemu) I see we associate a resamplefd with the
> umask function(vfio_pci_intx_unmask_handler in linux).
> 
>     irq_set = g_malloc0(argsz);
>     irq_set->argsz = argsz;
>     irq_set->flags = VFIO_IRQ_SET_DATA_EVENTFD | VFIO_IRQ_SET_ACTION_UNMASK;
>     irq_set->index = VFIO_PCI_INTX_IRQ_INDEX;
>     irq_set->start = 0;
>     irq_set->count = 1;
>     pfd = (int32_t *)&irq_set->data;
> 
>     *pfd = irqfd.resamplefd;
> 
>     ret = ioctl(vdev->vbasedev.fd, VFIO_DEVICE_SET_IRQS, irq_set);
> 
> I know this resamplefd is triggered when the interrupt controller receives
> an EOI and
> then we unmask and re-enabled the VFIO devices' interrupt.
> 
> So I think there  there must be a mask process(so we unmask it later), I
> mean there must a
> call of function vfio_pci_set_intx_mask(in linux).
> 
> What I can't understand is when this process(mask VFIO devices' interrupt)
> occurs?
It is done in the VFIO interrupt handler:
vfio_intx_handler/disable_irq_nosync for VFIO PCI (vfio_pci_intrs.c) or
vfio_automasked_irq_handler (vfio_platform_irq.c) for VFIO PLATFORM .

Thanks

Eric

> I only find a place(vfio_basic_config_write) calls vfio_pci_intx_mask> I 
> think when the guest process the interrupt it may mask this
> interrupt(finally call vfio_pci_set_intx_mask), but I can't find the code
> path related with vfio_basic_config_write.
> 
> 
> Any hints?
> 
> Thanks,
> Li Qiang
>