Comment 0 for bug 1805414

Description: kernel: zcrypt: reinit ap queue state machine

Symptom: Zcrypt ap queue device not operational at host level after a
              kvm guest used it.

Problem: The vfio device driver when receiving an ap queue device does
              additional resets thereby removing the registration for
              interrupts for the ap device done by the ap bus core
              code. So when later the vfio driver releases the device and
              one of the default zcrypt drivers takes care of the device
              the interrupt registration needs to get renewed. The current
              code does no renew and result is that requests send into such
              a queue will never see a reply processed - the application
              hangs.

Solution: This patch adds a function which resets the aq queue state
              machine for the ap queue device and triggers the walk through
              the initial states (which are reset and registration for
              interrupts). This function is now called before the driver's
              probe function is invoked.
              When the association between driver and device is released,
              the driver's remove function is called. The current
              implementation calls a ap queue function
              ap_queue_remove(). This invokation has been moved to the ap
              bus function to make the probe / remove pair for ap bus and
              drivers more symmetric.

Reproduction: Set up an kvm guest to use one or more ap queues in
              pass-through mode. Start the guest. Stop the guest. Reassign
              the ap resources back to the host system. Run an application
              which uses exactly this ap resources. Without the fix, the
              application hangs; with the fix the application should run
              fine.

Upstream commit(s):
104f708fd1241b22f808bdf066ab67dc5a051de5
Available on kernel.org