When adapters and/or domains are added to the host's AP configuration, this may result in multiple queue devices getting created and probed by the vfio_ap device driver. For each queue device probed, the matrix of adapters and domains assigned to a matrix mdev will be filtered to update the guest's APCB. If any adapters or domains get added to or removed from the APCB, the guest's AP configuration will be dynamically updated (i.e., hot plug/unplug). To dynamically update the guest's configuration, its VCPUs must be taken out of SIE for the period of time it takes to make the update. This is disruptive to the guest's operation and if there are many queues probed due to a change in the host's AP configuration, this could be troublesome. The problem is exacerbated by the fact that the 'on_scan_complete' callback also filters the mdev's matrix and updates the guest's AP configuration.
In order to reduce the potential amount of disruption to the guest that may result from a change to the host's AP configuration, let's bypass the filtering of the matrix and updating of the guest's AP configuration in the probe callback - if due to a host config change - and defer it until the 'on_scan_complete' callback is invoked after the AP bus finishes its device scan operation. This way the filtering and updating will be performed only once regardless of the number of queues added.
Signed-off-by: Tony Krowiak akrowiak@linux.ibm.com Fixes: eeb386aeb5b7 ("s390/vfio-ap: handle config changed and scan complete notification") Cc: stable@vger.kernel.org --- drivers/s390/crypto/vfio_ap_ops.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c index 08d612dfc506..7c2cd062ffe8 100644 --- a/drivers/s390/crypto/vfio_ap_ops.c +++ b/drivers/s390/crypto/vfio_ap_ops.c @@ -2102,9 +2102,22 @@ int vfio_ap_mdev_probe_queue(struct ap_device *apdev) if (matrix_mdev) { vfio_ap_mdev_link_queue(matrix_mdev, q);
+ /* + * If we're in the process of handling the adding of adapters or + * domains to the host's AP configuration, then let the + * vfio_ap device driver's on_scan_complete callback filter the + * matrix and update the guest's AP configuration after all of + * the new queue devices are probed. + */ + if (!bitmap_empty(matrix_mdev->apm_add, AP_DEVICES) || + !bitmap_empty(matrix_mdev->aqm_add, AP_DOMAINS)) + goto done; + if (vfio_ap_mdev_filter_matrix(matrix_mdev)) vfio_ap_mdev_update_guest_apcb(matrix_mdev); } + +done: dev_set_drvdata(&apdev->device, q); release_update_locks_for_mdev(matrix_mdev);