Managing use of storage by multiple pageable guests of a computing environment

1. A computer program product for facilitating management of storage of a computing environment that supports pageable guests, said computer program product comprising:

a non-transitory computer readable storage medium readable by a processor and storing instructions for execution by the processor for performing a method comprising:

detecting a storage protection fault in an attempt to access an area of storage that is protected by at least one of a host level of protection and a guest level of protection, wherein the area of storage specifies a first frame of host main storage;

determining whether the detected storage protection fault is due to the host level of protection or the guest level of protection, wherein the determining distinguishes between the storage protection fault being caused by host level protection or guest level protection;

responsive to the storage protection fault being due to the guest level of protection, performing a first action, the first action indicating storing is not permitted by the guest level of protection; and

responsive to the storage protection fault being due to the host level of protection, performing a second action, the second action comprising:

responsive to determining that the area of storage is part of a host copy-on-write scheme, assigning a second frame to the area of storage, copying contents of the first frame to the second frame, and permitting guest storing to the area of storage comprising the second frame; and

responsive to determining that the area of storage is not part of the host copy-on-write scheme, indicating storing is not permitted by the host level of protection.

2. The computer program product of claim 1 , wherein the storage protection fault is detected during execution of a pageable guest attempting access to the area of storage.

3. The computer program product of claim 2 , wherein the pageable guest is of one architecture and is executed by a host of another architecture different from the one architecture.

4. The computer program product of claim 1 , wherein the method further comprises obtaining information relating to the storage protection fault, the information comprising a host address or a guest address depending on whether the determining indicates the storage protection fault is due to the host level of protection or the guest level of protection, respectively.

5. The computer program product of claim 1 , wherein the attempt to access comprises issuing by a pageable guest an instruction that attempts to perform a store into the area of storage.

6. The computer program product of claim 1 , wherein the determining comprises performing one or more checks to determine which protection of a plurality of protections is denying access to the area of storage, and wherein a guest program encountering the storage protection fault is running on a host computer system.

7. The computer program product of claim 1 , wherein said method further comprises:

performing a guest interrupt, in response to the determining indicating that the detected storage protection fault is due to the guest level of protection; and

performing a host interrupt, in response to the determining indicating that the detected storage protection fault is not due to the guest level of protection.

8. The computer program product of claim 1 , wherein the guest level of protection is guest DAT protection, and the host level of protection is host DAT protection.

9. A method to facilitate management of storage of a computing environment that supports pageable guests, said method comprising:

detecting a storage protection fault in an attempt to access an area of storage that is protected by at least one of a host level of protection and a guest level of protection, wherein the area of storage specifies a first frame of host main storage;

determining whether the detected storage protection fault is due to the host level of protection or the guest level of protection, wherein the determining distinguishes between the storage protection fault being caused by host level protection or guest level protection;

responsive to the storage protection fault being due to the guest level of protection, performing a first action, the first action indicating storing is not permitted by the guest level of protection; and

responsive to the storage protection fault being due to the host level of protection, performing a second action, the second action comprising:

responsive to determining that the area of storage is part of a host copy-on-write scheme, assigning a second frame to the area of storage, copying contents of the first frame to the second frame, and permitting guest storing to the area of storage comprising the second frame; and

responsive to determining that the area of storage is not part of the host copy-on-write scheme, indicating storing is not permitted by the host level of protection.

10. The method of claim 9 , wherein the storage protection fault is detected during execution of a pageable guest attempting access to the area of storage.

11. The method of claim 9 , further comprising obtaining information relating to the storage protection fault, the information comprising a host address or a guest address depending on whether the determining indicates the storage protection fault is due to the host level of protection or the guest level of protection, respectively.

12. The method of claim 9 , wherein the attempt to access comprises issuing by a pageable guest an instruction that attempts to perform a store into the area of storage.

13. The method of claim 9 , wherein the determining comprises performing one or more checks to determine which protection of a plurality of protections is denying access to the area of storage, and wherein a guest program encountering the storage protection fault is running on a host computer system.

14. The method of claim 9 , wherein said method further comprises:

performing a guest interrupt, in response to the determining indicating that the detected storage protection fault is due to the guest level of protection; and

performing a host interrupt, in response to the determining indicating that the detected storage protection fault is not due to the guest level of protection.

15. A computer system for facilitating management of storage of a computing environment that supports pageable guests, said computer system comprising:

a memory; and

a processor in communications with the memory, wherein the computer system is configured to perform a method, said method comprising:

detecting a storage protection fault in an attempt to access an area of storage that is protected by at least one of a host level of protection and a guest level of protection, wherein the area of storage specifies a first frame of host main storage;

determining whether the detected storage protection fault is due to the host level of protection or the guest level of protection, wherein the determining distinguishes between the storage protection fault being caused by host level protection or guest level protection;

responsive to the storage protection fault being due to the guest level of protection, performing a first action, the first action indicating storing is not permitted by the guest level of protection; and

responsive to the storage protection fault being due to the host level of protection, performing a second action, the second action comprising:

responsive to determining that the area of storage is part of a host copy-on-write scheme, assigning a second frame to the area of storage, copying contents of the first frame to the second frame, and permitting guest storing to the area of storage comprising the second frame; and

responsive to determining that the area of storage is not part of the host copy-on-write scheme, indicating storing is not permitted by the host level of protection.

16. The computer system of claim 15 , wherein the storage protection fault is detected during execution of a pageable guest attempting access to the area of storage.

17. The computer system of claim 15 , wherein the method further comprises obtaining information relating to the storage protection fault, the information comprising a host address or a guest address depending on whether the determining indicates the storage protection fault is due to the host level of protection or the guest level of protection, respectively.

18. The computer system of claim 15 , wherein the attempt to access comprises issuing by a pageable guest an instruction that attempts to perform a store into the area of storage.

19. The computer system of claim 15 , wherein the determining comprises performing one or more checks to determine which protection of a plurality of protections is denying access to the area of storage, and wherein a guest program encountering the storage protection fault is running on a host computer system.

20. The computer system of claim 15 , wherein the method further comprises:

performing a guest interrupt, in response to the determining indicating that the detected storage protection fault is due to the guest level of protection; and

performing a host interrupt, in response to the determining indicating that the detected storage protection fault is not due to the guest level of protection.