Operational considerations
Global, system-wide control of Dynamic I/O Configuration is provided by the I/O Configuration Control Authority. Use of this facility does not result in strict separation of partitions and was not included in the evaluated product. At most, only use the Customize/Delete Activation Profiles task to open a reset or image profile to enable I/O Configuration control for a logical partition. The I/O configuration control selection is located on the Security page for the logical partition. See Input/output (I/O) configuration control for more information.
Logical partitions may also be defined with their Logical Partition Isolation security control enabled. For such logical partitions, an offline, reconfigurable CHPIDs cannot be assigned to another logical partition unless the Release I/O Path task is invoked (or the Reassign I/O Path task) by the System Administrator from the SE or HMC. These tasks are available from the Channel Operations task list. The CHPID statement's candidate list can be used to limit the "mobility" of a reconfigurable channel. The system will only accept configure on commands for CHPIDS in partitions specified in the candidate list of the target channel path.
All channel path reconfiguration procedures should be specifically described in the secure installation's procedures. Any not described, must not be permitted. While developing these procedures, consideration must be given to the security implications of defining a channel path (and its attached devices) to be reconfigurable. Specifically, which from-to pairs of logical partitions are valid? (When this has been established, candidate lists are the means for implementing this aspect of the installation's security policy). In the process of reconfiguration, could data be passed from one logical partition to another via one of the attached devices? What other procedural controls must be followed in order that your organization's security policy is maintained? What operator actions are required to reconfigure this specific channel path in a secure manner? Lastly, careful attention to the IOCDS language rules relating to the CHPID REC parameter is necessary to achieve the result desired.
Channel path reassignments which result from executing configure CHPID actions, are remembered by the system by recording these changes on the SE hard drive and associating them with the IOCDS (the IOCDS itself is not changed). These changes to channel path assignments (I/O Configuration) take effect whenever the logical partitions are again activated. If the IOCDS is rewritten (by invoking HCD or IOCP), the channel path reassignments are erased (at the first Activation using that newly rewritten IOCDS).
When a channel path is deconfigured from a logical partition, each subchannel (an internal structure that provides the logical appearance of an I/O device, and is uniquely associated with one I/O device) for which this channel path is the only (remaining) online path, is removed from the logical partition. Before the subchannels are removed, they are drained and disabled. Subsequently the channel path is reset. If the channel path being deconfigured is the last channel path to a device, that device is also reset. Actions directed to a removed subchannel result in a condition code=3 (not operational).
At that very first use of a newly created IOCDS, activation configures all channel paths to the logical partitions as defined by the IOCDS. The subsequent movements of reconfigurable channel paths, from one logical partition to another, is remembered by the system. During subsequent activations, as each logical partition is activated, if a channel path was (previously) moved out of a logical partition, the channel path is taken offline to that logical partition; if a channel path was moved into a logical partition, the channel path is brought on line to that logical partition. These logical configuration changes can be viewed by performing the following steps:
- Go to the Configuration task list
- Select Input/Output (I/O) Configuration task
- Select the IOCDS which is marked Active
- Select the View pulldown
- In the View pulldown, select Channel Path Configuration
- Select a PCHID
- Select the View pulldown
- In the View pulldown, select CHPID information
The Security Administrator can repeat the final three steps shown above to see all defined CHPIDS and determine which partition(s) each is assigned to, whether they are Dedicated, Shared or Reconfigurable, and the type of each CHPID. In a secure installation, CHPIDs must not be shared among Isolated logical partitions.
Careful review of installation security guidelines must precede using the Swap Channel Path procedure. All devices attached to the channel path being switched in, may be accessible to the logical partition. This caution does not apply to a truly "spare" channel path, one with no devices currently defined or attached.