A special external interrupt, code 1'4001' notifies a virtual machine
of a pendingVirtual Machine Communication Facility request. The XINTBLOK for this interrupt is set up with an XINTSORT field of
I'7FFFFFFF', the lowest priority.System Support FREE STORAGE MANAGEMENT During its execution, CP occasionally requires small blocks of storage
that areused for the duration of a task. CP obtains this storage from the free storage area. The free storage area is divided into various
size subpools. Therequester informs the free storage manager of the
size of theblock required and the smallest available subpool that
fulfills the request is allocated to the requester.When the block is
no longer needed, the requester informs the free storage manager andCP returns the block to free storage.
If the request for free storage cannot be fulfilled, the free storage
aanager requests the teaporary use of a page of storagefrom the dynaBic
paging area. If a page is obtained, the page is chained to the free
storage area and used for that purpose until it is no longer needed and
subsequently returned to thedynamic paging area.
If the request for a page cannot be fulfilled; the requesterwaits until free storage becomes available. STORAGE PROTECTION VM/370 provides both fetch and store protection for real storage. The
contents of real storage are protected froa destruction ormisuse caused
by erroneous or unauthorized storing of fetching by the program.Storage is protected from improper storing or from both improper storing
and fetching, but not from improper fetching alone.When the processor accesses storage, and protection applies, the
protectionkey of the current PSW is used as the co.parand. The
protectionkey of the processor is bit positions 8-11 of the PSi. If the processor access is prohibited because of
violation, the operation is suppressed or terminated,
interruption for a protection exception takes place.
a protection
and aprogram When the reference is made to a channel, and protection applies, the
protectionkey associated with the I/O operation is used as the comparand. The protection key for an I/O operation is in bit positions 0-3 of the CAW and is recorded in bit positions 0-3 of the CSi stored as
a result of an I/O operation. If channel access is prohibited, theCSi stored as a result of the operation indicates a protection-check
condition.When a storage access is prohibited because of a store protection
violation, the contents of the protected location remain unchanged. If
a fetch protection violation occurs, the protected information is not
loaded into an addressable register, moved to anotherstorage location,
or provided to an I/O device.CP Introduction 1-77
of a pending
I'7FFFFFFF', the lowest priority.
that are
size subpools. The
size of the
fulfills the request is allocated to the requester.
no longer needed, the requester informs the free storage manager and
If the request for free storage cannot be fulfilled, the free storage
aanager requests the teaporary use of a page of storage
paging area. If a page is obtained, the page is chained to the free
storage area and used for that purpose until it is no longer needed and
subsequently returned to the
If the request for a page cannot be fulfilled; the requester
contents of real storage are protected froa destruction or
by erroneous or unauthorized storing of fetching by the program.
and fetching, but not from improper fetching alone.
protection
protection
violation, the operation is suppressed or terminated,
interruption for a protection exception takes place.
a protection
and a
protection
a result of an I/O operation. If channel access is prohibited, the
condition.
violation, the contents of the protected location remain unchanged. If
a fetch protection violation occurs, the protected information is not
loaded into an addressable register, moved to another
or provided to an I/O device.