Re: [PATCH v5 07/21] KVM: selftests: Verify IRQ bypass works in IRQ test

[Sean Christopherson <seanjc@google.com>]

On Thu, Jun 04, 2026, Sean Christopherson wrote:
> The shortlog is at best misleading.  There are zero guarantees that IRQ bypass
> is supported and enabled.
> 
> On Thu, Jun 04, 2026, Josh Hilke wrote:
> > From: David Matlack <dmatlack@google.com>
> > 
> > Trigger interrupts from a VFIO device instead of emulating interrupts
> 
> It's not emulating, it's synthesizing.  Emulating implies there's a device of
> some kind that the test is mimicking.
> 
> > using KVM eventfds. This verifies that guests receive interrupts via IRQ
> > bypass.
> 
> No, it verifies that delivery of a VFIO MSI-X through VFIO=>KVM works, and *may*
> verify IRQ bypass.  And all of that very much relies on the eventfds to be in
> place.
> 
> > @@ -119,7 +160,17 @@ int main(int argc, char **argv)
> >  	vm = vm_create_with_vcpus(nr_vcpus, guest_code, vcpus);
> >  	vm_install_exception_handler(vm, vector, guest_irq_handler);
> >  
> > -	eventfd = kvm_new_eventfd();
> > +	if (device_bdf) {
> > +		iommu = iommu_init(default_iommu_mode);
> 
> This needs:
> 
> diff --git tools/testing/selftests/kvm/irq_test.c tools/testing/selftests/kvm/irq_test.c
> index cf4568718cee..2e7e100d4815 100644
> --- tools/testing/selftests/kvm/irq_test.c
> +++ tools/testing/selftests/kvm/irq_test.c
> @@ -235,6 +235,8 @@ int main(int argc, char **argv)
>         }
>  
>         if (device_bdf) {
> +               __open_path_or_exit("/dev/iommu", O_RDONLY, "Is IOMMUFD available?");
> +
>                 iommu = iommu_init(default_iommu_mode);

*sigh* 

<rant>
This is beyond frustating.  I have A PERFECTLY FUNCTIONAL KERNEL, but this test
VERY SUBTLY "defaults" to IOMMUFD.  ARGH!!!!!

And to make matters worse, if I enable CONFIG_IOMMUFD, but don't enable
CONFIG_VFIO_DEVICE_CDEV, then AFAICT, I can't do a damn thing with VFIO.  I dunno,
I can't get IOMMUFD to work even with that.

Worst of all, the changelog SAYS BLOODY NOTHING ABOUT THIS.
</rant>

Please, for the love of all that is holy, when sending stuff upstream, think about
how your code will impact people and environments outside the world of Google.
And more importantly, *test* your code beyond Google's highly curated environment.