linux-kernel - Re: [PATCH v3 0/4] vfio: selftests: update DMA mapping tests to use queried IOVA ranges

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Message-ID: <aRTMO7GtBTcxaPj5@devgpu015.cco6.facebook.com>
Date: Wed, 12 Nov 2025 10:04:43 -0800
From: Alex Mastro <amastro@...com>
To: David Matlack <dmatlack@...gle.com>
CC: Alex Williamson <alex@...zbot.org>, Shuah Khan <shuah@...nel.org>,
        Jason
 Gunthorpe <jgg@...pe.ca>, <kvm@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 0/4] vfio: selftests: update DMA mapping tests to use
 queried IOVA ranges

On Wed, Nov 12, 2025 at 09:51:35AM -0800, David Matlack wrote:
> On Wed, Nov 12, 2025 at 9:40 AM Alex Mastro <amastro@...com> wrote:
> >
> > Hey David, is vfio_pci_driver_test known to be in good shape? Both on the base
> > commit and after my series, I am seeing below, which results in a KSFT_SKIP.
> > Invoking other tests in a similar way actually runs things with expected
> > results (my devices are already bound to vfio-pci before running anything).
> >
> > base commit: 0ed3a30fd996cb0cac872432cf25185fda7e5316
> >
> > $ vfio_pci_driver_test -f 0000:05:00.0
> > No driver found for device 0000:05:00.0
> >
> > Same thing using the run.sh wrapper
> >
> > $ sudo ./run.sh -d 0000:05:00.0 ./vfio_pci_driver_test
> > + echo "0000:05:00.0" > /sys/bus/pci/drivers/vfio-pci/unbind
> > + echo "vfio-pci" > /sys/bus/pci/devices/0000:05:00.0/driver_override
> > + echo "0000:05:00.0" > /sys/bus/pci/drivers/vfio-pci/bind
> >
> > No driver found for device 0000:05:00.0
> > + echo "0000:05:00.0" > /sys/bus/pci/drivers/vfio-pci/unbind
> > + echo "" > /sys/bus/pci/devices/0000:05:00.0/driver_override
> > + echo "0000:05:00.0" > /sys/bus/pci/drivers/vfio-pci/bind
> >
> > device = vfio_pci_device_init(device_bdf, default_iommu_mode);
> > if (!device->driver.ops) {
> >         fprintf(stderr, "No driver found for device %s\n", device_bdf);
> >         return KSFT_SKIP;
> > }
> >
> > Is this meant to be a placeholder for some future testing, or am I holding
> > things wrong?
> 
> What kind of device are you using?
> 
> This test uses the selftests driver framework, so it requires a driver
> in tools/testing/selftests/vfio/lib/drivers to function. The driver
> framework allows tests to trigger real DMA and MSIs from the device in
> a controlled, generic, way.

Ah, TIL about that concept. This is with one of our internal compute
accelerators, so not surprising that I'm seeing a skip then.

> We currently only have drivers for Intel DSA and Intel CBDMA
> devices.So if you're not using one of those devices,
> vfio_pci_driver_test exiting with KSFT_SKIP is entirely expected.
> 
> I would love to add support for more devices. Jason Gunthrope
> suggested supporting a driver for mlx5 class hardware, since it's
> broadly available. I've also had some discussions about adding a
> simple emulated PCIe device to QEMU for running VFIO selftests within
> VMs.

I do have access to mlx5 hardware FWIW, so that would be cool.

Thanks for the explanation!

Alex