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[Qemu-devel] Question about the vfio device interrupt

From: Li Qiang
Subject: [Qemu-devel] Question about the vfio device interrupt
Date: Wed, 15 May 2019 18:01:22 +0800

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->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)
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?

Li Qiang

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