Re: [PATCH v5 17/20] vfio: selftests: Add vfio_pci_liveupdate_kexec_test

[Vipin Sharma <vipinsh@google.com>]

On Tue, Aug 04, 2026 at 03:19:34PM -0700, Yanjun.Zhu wrote:
> 
> On 7/14/26 8:15 AM, Vipin Sharma wrote:
> > Add a selftest to exercise preserving a vfio-pci device across a Live
> > Update. For now the test is extremely simple and just verifies that the
> > device file can be preserved and retrieved. In the future this test will
> > be extended to verify more parts about device preservation as they are
> > implemented.
> > 
> > This test is added to TEST_GEN_PROGS_EXTENDED since it must be run
> > manually along with a kexec.
> > 
> > To run this test manually:
> > 
> >   $ tools/testing/selftests/vfio/scripts/setup.sh 0000:00:04.0
> >   $ tools/testing/selftests/vfio/vfio_pci_liveupdate_kexec_test --stage 1 0000:00:04.0
> > 
> >   $ kexec ...   # NOTE: Exact method will be distro-dependent
> > 
> >   $ tools/testing/selftests/vfio/scripts/setup.sh 0000:00:04.0
> >   $ tools/testing/selftests/vfio/vfio_pci_liveupdate_kexec_test --stage 2 0000:00:04.0
> Hi, Vipin
> 
> Thanks a lot for your help. I followed your suggestion, vfio-pci setup can
> work.

I am glad your setup using virsh is working.

> 
> The followings are the test result. In the step 3, after kexec, there are
> some fails. I am not sure if these are known problem or not.
> 
> 1. Before kexec command
> 
> + modprobe -v vfio-pci
> + tools/testing/selftests/vfio/scripts/setup.sh 0000:00:04.0
> + echo "vfio-pci" > /sys/bus/pci/devices/0000:00:04.0/driver_override
> + echo "0000:00:04.0" > /sys/bus/pci/drivers/vfio-pci/bind
> + tools/testing/selftests/vfio/vfio_pci_liveupdate_kexec_test --stage 1
> 0000:00:04.0
> Preserving device in session
> Preserving memfd of size 0x40100000 in session
> # [STAGE 1] Forking persistent child to hold sessions...
> # [STAGE 1] Child PID: 1236. Resources are pinned.
> # [STAGE 1] You may now perform kexec reboot.
> + set +x
> 
> 2. Run kexec command
> 
> 3. After kexec command
> 
> + echo "vfio-pci" > /sys/bus/pci/devices/0000:00:04.0/driver_override
> + echo "0000:00:04.0" > /sys/bus/pci/drivers/vfio-pci/bind
> Checking open(/dev/vfio/devices/vfio0) fails  <--- I can confirm that the
> /dev/vfio/devices/vfio0 exists. But open this failed.

This is correct output. Test is verifying that open should fail. If it
didn't fail the ntest would have exited with an error. A preserved VFIO
FD can only be retrived using Live Update session ioctls and not through
usual VFIO dev path.

> Checking ioctl(group_fd, VFIO_GROUP_GET_DEVICE_FD, "0000:00:04.0") fails
> (vfio_type1_iommu)      <--- fails
> Checking ioctl(group_fd, VFIO_GROUP_GET_DEVICE_FD, "0000:00:04.0") fails
> (vfio_type1v2_iommu).  <--- fails
> Checking ioctl(group_fd, VFIO_GROUP_GET_DEVICE_FD, "0000:00:04.0") fails
> (iommufd_compat_type1)  <--- fails
> Checking ioctl(group_fd, VFIO_GROUP_GET_DEVICE_FD, "0000:00:04.0") fails
> (iommufd_compat_type1v2). <--- fails

These are all correct output. Test is verifying that userspace should
not be able to get VFIO device FD only through Live Update session
ioctls and nothing else.

> Retrieving memfd from LUO
> Finishing the session before retrieving the device (should fail)
> Retrieving the device FD from LUO
> Finishing the session before binding to iommufd (should fail)
> Binding the device to an iommufd and setting it up
> Finishing the session
> 

This is shows VFIO FD is successfully retrived by Live Update ioctl.

So, you saw expected output from successful test run. I will change
the message getting printed to avoid confusion. I think current way of
printing ".... fails" is confusing.

Thanks
Vipin