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

Matthew Rosato
2023-05-31T14:48:34Z

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@linux.ibm.com>

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

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(-)
>