Selecting the storage key

The storage key helps control read and write access to the virtual storage area. You need to choose a storage key that will allow access by those programs that require it. To limit unwanted access by other programs, try to select a storage key different from the PSW key that other programs are likely to use.

The storage key controls user access as follows:

Programs running in PSW key 0 have read and write access to storage in every storage key.
Programs running in PSW keys 1 through 15 have read access to:
- Storage whose key matches their PSW key
- Storage (in any key) that's not fetch protected
- Storage in key 9 if the hardware feature, subsystem storage protection override, is installed. The CVTOVER bit in the CVT is set to 1 if the feature is installed. For more information about the CVTOVER bit in the CVT, see z/OS MVS Data Areas in the z/OS Internet library.
Programs running in PSW keys 1 through 15 have write access to:
- Storage whose key matches their PSW key
- Storage in key 9, if subsystem storage protection override is installed.

The amount of control you have over the storage key assigned to your virtual storage request varies depending on the subpool from which you request storage. For the purpose of storage key assignment, there are three types of subpools. The first type of subpool is always assigned a particular storage key, such as 0. The second type of subpool is assigned its storage key based on the key in the requesting task's TCB at the time of that task's first storage request. The third type of subpool allows you to select the storage key by:

Specifying the KEY parameter on the STORAGE, GETMAIN, or FREEMAIN macros, or the CPOOL macro with the BUILD parameter.
Choosing a particular macro and set of parameters for the storage request. (The combination of macro and parameters determines the key assigned to the storage request for these subpools.)
Specifying CALLRKY=YES on the STORAGE macro, which causes the storage key to match the calling program's current PSW key.

These subpools are shown in the subpool table (Table 1) as having a selectable storage key. Detailed information about subpools with selectable storage keys is provided in Table 1.

Table 1. Storage Keys for Selectable Key Subpools
Subpool	Macros and Parameters	Storage Key
129-132	GETMAIN with LC, LU, VC, VU, EC, EU, or R; BRANCH not specified FREEMAIN with LC, LU, L, VC, VU, V, EC, EU, E, or R; BRANCH not specified STORAGE with OBTAIN or RELEASE; CALLRKY=YES is specified	The storage key equals the caller's PSW key. (The KEY parameter is not allowed.)
129-132	GETMAIN with LC, LU, VC, VU, EC, EU, or R; BRANCH=YES specified FREEMAIN with LC, LU, L, VC, VU, V, EC, EU, E, or R; BRANCH=YES specified	The storage key is 0. (The KEY parameter is not allowed.)
129-132	GETMAIN with RC, RU, VRC, VRU; BRANCH not specified FREEMAIN with RC, RU; BRANCH not specified CPOOL with BUILD	The storage key is the key the caller specifies on the KEY parameter. If KEY is not specified, the default equals the caller's PSW key.
129-132	GETMAIN with RC, RU, VRC, VRU; BRANCH=YES specified FREEMAIN with RC, RU; BRANCH=YES specified STORAGE with OBTAIN or RELEASE; CALLRKY=YES is omitted, or CALLRKY=NO is specified	The storage key is the key the caller specifies on the KEY parameter. If KEY is not specified, the default is 0.
227-231, 241, 249	All GETMAIN requests with BRANCH not specified All FREEMAIN requests with BRANCH not specified STORAGE with OBTAIN or RELEASE; CALLRKY=YES specified	The storage key equals the caller's PSW key. (For RC, RU, VRC, and VRU, the KEY parameter is ignored. For other GETMAIN and FREEMAIN requests, the KEY parameter is not allowed.)
227-231, 241, 249	GETMAIN with LC, LU, VC, VU, EC, EU, or R; BRANCH=YES specified FREEMAIN with LC, LU, L, VC, VU, V, EC, EU, E, or R; BRANCH=YES specified	The storage key is 0 (The KEY parameter is not allowed.)
227-231, 241, 249	GETMAIN with RC, RU, VRC, VRU; BRANCH specified Note: BRANCH=(YES,GLOBAL) is not valid for subpools 229, 230, and 249. FREEMAIN with RC, RU; BRANCH specified Note: BRANCH=(YES,GLOBAL) is not valid for subpools 229, 230, and 249. STORAGE with OBTAIN or RELEASE; CALLRKY=YES omitted, or CALLRKY=NO specified	The storage key is the key the caller specifies on the KEY parameter. If KEY is not specified, the default is 0.
227-231, 241, 249	CPOOL with BUILD	The storage key is the key the caller specifies on the KEY parameter. If KEY is not specified, the default equals the caller's PSW key.