Re: [PATCH 3/3] KVM: selftests: Use VFIO selftests library to pick IOMMU mode in IRQ test

[David Matlack <dmatlack@google.com>]

On 2026-11-02 07:35 AM, Sean Christopherson wrote:
> On Mon, Nov 02, 2026, Sean Christopherson wrote:
> > On Thu, Oct 29, 2026, David Matlack wrote:
> > >  static void help(const char *name)
> > >  {
> > >  	printf("Usage: %s [-a] [-d <segment:bus:device.function>] [-e] [-h] [-i nr_irqs] [-m] [-n] [-t iommu_type] [-v nr_vcpus] [-x]\n", name);
> > > @@ -266,8 +250,7 @@ int main(int argc, char **argv)
> > >  	}
> > >  
> > >  	if (device_bdf) {
> > > -		if (!iommu_type)
> > > -			iommu_type = probe_iommu_type();
> > > +		TEST_REQUIRE(iommu_mode_is_available(iommu_type));
> > 
> > This is very unhelpful when neither IOMMUFD nor VFIO is available, especially
> > why the user doesn't explicitly provide the desired mode:
> > 
> >   # ./irq_test -d 0000:6f:01.0 -i 10000
> >   Random seed: 0x79d386bd
> >   1..0 # SKIP - Requirement not met: iommu_mode_is_available(iommu_type)

Agreed, that is not very helpful. I've added a
iommu_mode_unavailable_msg() helper to libvfio, which returns the reason
a given mode (or any mode, if NULL) is not available. So irq_test would
have:

    __TEST_REQUIRE(iommu_mode_is_available(iommu_type), "%s",
               iommu_mode_unavailable_msg(iommu_type));

which gives:

  # ./irq_test -d 0000:01:00.0 -t iommufd
  1..0 # SKIP - IOMMU mode 'iommufd' is not available
  # ./irq_test -d 0000:01:00.0
  1..0 # SKIP - No IOMMU mode is available. Is VFIO (or IOMMUFD) loaded and enabled?

> Side topic, it would be nice if iommu_mode_lookup() printed out the known modes
> when this is hit:
> 
> 	VFIO_FAIL("Unrecognized IOMMU mode: %s\n", iommu_mode);

Will do in v2. And I will also use the same helper to print out the list
of known modes in irq_test -h.