Re: [PATCH 0/3] s390/vfio-ap: fix hang when mdev attached to guest is removed

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On 5/31/23 10:48 AM, Matthew Rosato wrote:
On 5/30/23 6:35 PM, Tony Krowiak wrote:
When a user attempts to remove a vfio-ap mediated device attached to a
guest, the operation hangs until the mdev's fd is closed by the guest
(i.e., the hostdev is detached or the guest is shut down). This patch
series provides kernel-side code that allows userspace to set up a
communication channel that will allow the vfio_ap device driver to notify
userspace when a request to release the mdev is received, so that userspace
can close the mdev fd and avoid the hang. The patch series provides the
following:

1. Introduces code to handle the VFIO_DEVICE_GET_IRQ_INFO and
    VFIO_DEVICE_SET_IRQS ioctl calls to set the eventfd_ctx for signaling a
    device request to userspace.

2. Wires up the VFIO bus driver callback to request a release of the mdev.
    When invoked, the vfio_ap device driver will use the eventfd_ctx set up
    in #1 to signal a request to userspace to release the mdev.


Note:
----
If a user subsequently attempts to restart the guest or re-attach the mdev,
the operation will fail with a message indicating the domain is already
active. This is a libvirt problem resolved with the following commit:

commit ebd004a03dbd ("security: do not remember/recall labels for VFIO
MDEVs")

For the series:

Reviewed-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>

Thanks for the review.



I also did some testing using the companion qemu series at
https://lore.kernel.org/qemu-devel/20230530225544.280031-1-akrowiak@xxxxxxxxxxxxx

Shall I credit you with Tested-by also?


Before kernel+qemu changes:
1. mdevctl start -u <uuid>, where <uuid> references a vfio-ap mdev
2. start a qemu guest with <uuid> attached
3. mdvectl stop -u <uuid>
4. -mdevctl will now hang indefinitely; the mdev remains in-use by the guest-
Note: detaching the device or powering off the guest will allow the mdevctl command to complete.

After kernel+qemu changes:
1. mdevctl start -u <uuid>, where <uuid> references a vfio-ap mdev
2. start a qemu guest with <uuid> attached
3. mdvectl stop -u <uuid>
4. -device is detached from the guest and stopped-
5. Using a libvirt that includes ebd004a03dbd I also verified that the mdev can be started again and re-attached to the running guest without error.



Tony Krowiak (3):
   vfio: ap: realize the VFIO_DEVICE_GET_IRQ_INFO ioctl
   vfio: ap: realize the VFIO_DEVICE_SET_IRQS ioctl
   s390/vfio-ap: Wire in the vfio_device_ops request callback

  drivers/s390/crypto/vfio_ap_ops.c     | 134 +++++++++++++++++++++++++-
  drivers/s390/crypto/vfio_ap_private.h |   3 +
  include/uapi/linux/vfio.h             |   9 ++
  3 files changed, 145 insertions(+), 1 deletion(-)





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