Re: [PATCH v6 07/18] KVM: selftests: Add VFIO device support to eventfd IRQ test

[Sean Christopherson <seanjc@google.com>]

On Wed, Jun 10, 2026, sashiko-bot@kernel.org wrote:
> > diff --git a/tools/testing/selftests/kvm/irq_test.c b/tools/testing/selftests/kvm/irq_test.c
> > index 9f8895b898214..6888be54ee4a9 100644
> > --- a/tools/testing/selftests/kvm/irq_test.c
> > +++ b/tools/testing/selftests/kvm/irq_test.c
> 
> [ ... ]
> 
> > @@ -74,11 +107,29 @@ static void kvm_route_msi(struct kvm_vm *vm, u32 gsi, struct kvm_vcpu *vcpu,
> >  	vm_ioctl(vm, KVM_SET_GSI_ROUTING, &routing.header);
> >  }
> >  
> > +static const char *probe_iommu_type(void)
> > +{
> > +	int io_fd;
> > +
> > +	io_fd = open("/dev/iommu", O_RDONLY);
> > +	if (io_fd >= 0) {
> > +		close(io_fd);
> > +		return MODE_IOMMUFD;
> > +	}
> > +
> > +	io_fd = __open_path_or_exit("/dev/vfio", O_RDONLY,
> > +				    "Is VFIO (or IOMMUFD) loaded and enabled?");
> > +	close(io_fd);
> 
> [Severity: Medium]
> The commit message states that the test will auto-probe IOMMUFD vs legacy
> VFIO and skip the test if neither is available. However, probe_iommu_type()
> calls __open_path_or_exit() on /dev/vfio.
> 
> Because /dev/vfio is a directory, open() with O_RDONLY will succeed if the
> directory exists (e.g., created by udev or left over after a module unload),
> even if the VFIO module is not loaded and the character device is absent.
> Opening a directory does not trigger the kernel's character device module
> autoloading.
> 
> If this occurs, probe_iommu_type() incorrectly assumes VFIO is available and
> returns MODE_VFIO_TYPE1_IOMMU. The test then calls iommu_init(), which attempts
> to open /dev/vfio/vfio and will fatally abort, resulting in a test crash rather
> than a clean skip.
> 
> Additionally, using __open_path_or_exit() will cause the test to exit rather
> than skip if the path does not exist.
> 
> Should this probe instead check for the /dev/vfio/vfio character device and
> use open() instead of __open_path_or_exit() to allow the test to gracefully
> skip and trigger module autoloading?

No, "probe" here means guessing which flavor of VFIO vs. IOMMUFD, it doesn't
mean probing a kernel module.