Seeking clarification to the original question I posted:
>>
>>
> This maybe a novice question - Would appreciate it if you can you provide
a
> pointer to documentation or relevant code that explains what is the
> *limitation in supporting level irq support in kvm irqfd.*
>
>
>
After browsing the KVM kernel code, it does look like direct assignment of
PCI devices allows support for level-triggered interrupts to be injected to
the guest from the kernel.  (*as opposed to not supporting it for vhost
irqfd mechanism*)
This occurs when the guest device supports INTX.
Reference:  kvm_assigned_dev_interrupt_work_handler() in assigned-dev.c
calls kvm_set_irq()
with the guest_irq.
This function in turn invokes the assigned set function  (either
kvm_set_pic_irq or kvm_set_ioapic_irq) which was setup at kvm_irq_chip
creation time when kvm_setup_default_irq_routing () called for handling
ioctl KVM_CREATE_IRQCHIP.

So, it isn't clear why level-triggered interrupt isn't supported for irqfd
mechanism.
Would greatly appreciate clarification here

Thanks
-Rukhsana