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The APCB is a field within the CRYCB that provides the AP configuration to a KVM guest. Let's introduce a shadow copy of the KVM guest's APCB and maintain it for the lifespan of the guest. The shadow APCB serves the following purposes: 1. The shadow APCB can be maintained even when the mediated device is not currently in use by a KVM guest. Since the mediated device's AP configuration is filtered to ensure that no AP queues are passed through to the KVM guest that are not bound to the vfio_ap device driver or available to the host, the mediated device's AP configuration may differ from the guest's. Having a shadow of a guest's APCB allows us to provide a sysfs interface to view the guest's APCB even if the mediated device is not currently passed through to a KVM guest. This can aid in problem determination when the guest is unexpectedly missing AP resources. 2. If filtering was done in-place for the real APCB, the guest could pick up a transient state. Doing the filtering on a shadow and transferring the AP configuration to the real APCB after the guest is started or when AP resources are assigned to or unassigned from the mediated device, or when the host configuration changes, the guest's AP configuration will never be in a transient state. Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com> Reviewed-by: Halil Pasic <pasic@linux.ibm.com> Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com> |
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