The PROTECT option of PGSER makes a range of virtual storage pages read-only and helps to improve data integrity. The UNPROTECT option of PGSER makes a range of virtual storage pages modifiable and provides a supported way of modifying the PLPA on an IPLed system. Note, however, that PLPA modifications made this way exist only for the life of the IPL.
IBM® recommends that you use PGSER PROTECT only for full pages of storage on page boundaries. This usage avoids making other areas of storage read-only unintentionally. For instance, if you obtain a virtual storage area smaller than a page and then issue PGSER PROTECT, the entire page is made read-only, including the portion of the page that is not part of your storage area.
PROTECT and UNPROTECT apply only to virtual storage pages. The system does not keep track of how many times a page has been protected or unprotected. One UNPROTECT cancels all PROTECTs for a given page.