Dynamic address translation with DAT protection

A system for protecting data in a computer system of a machine architecture, the system comprising:

• a computer memory capable of storing machine instructions and a hierarchy of translation tables used for dynamic address translation of a virtual address into a real address or absolute address of a desired block of data in said main storage, said real address being subject to a prefixing operation;
• and
• a processor in communication with said computer memory, said processor capable of accessing said hierarchy of translation tables stored in said memory, said processor performing a method comprising:
• obtaining a virtual address of a desired block of main storage to be translated;
• obtaining an initial origin address of a translation table of a hierarchy of translation tables, said hierarchy of translation tables comprising a segment table;
• based on the obtained initial origin address and the obtained virtual address, performing a dynamic address translation to obtain a segment table entry from said segment table, said segment table entry configured to contain a format control field, said format control field, when enabled indicating the segment table entry consists of a first format of fields, said format control field when not-enabled, indicating the segment table entry consists of a second format of fields, the first format of fields including a dynamic address translation (DAT) protection field (P), the second format of fields absent the DAT protection field;
• in response to an enhanced dynamic address translation (eDAT) facility being enabled, wherein translation table entries of the hierarchy of translation tables used in said dynamic address translation, other than the segment table entry, comprise DAT protection fields, determining whether said format control field in said segment table entry is enabled;
• and
• in response to said format control field being enabled, performing:
• obtaining from said segment table entry a segment-frame absolute address of a large block of data in main storage and a first DAT protection field;
• combining said obtained segment-frame absolute address with a page index portion of said virtual address and a byte index portion of said virtual address to form the translated address of the desired block of main storage within said large block of main storage, said desired block of main storage consisting of one or more bytes of data;
• determining whether any DAT protection fields in any translation table entries used in said performed dynamic address translation of said virtual address are enabled;
• and
• in response to all of said DAT protection fields being not enabled, permitting store operations to said desired block of main storage in response to said store operations being associated with said performed address translation.

A method for protecting data in a computer system of a machine architecture having a CPU, a memory, and a hierarchy of translation tables used for translation of a virtual address into a translated address of a block of data in main storage, the method comprising:

• obtaining a virtual address of a desired block of main storage to be translated;
• obtaining an initial origin address of a translation table of a hierarchy of translation tables, said hierarchy of translation tables comprising a segment table;
• based on the obtained initial origin address and the obtained virtual address, performing a dynamic address translation to obtain a segment table entry from said segment table, said segment table entry configured to contain a format control field, said format control field, when enabled indicating the segment table entry consists of a first format of fields, said format control field when not-enabled, indicating the segment table entry consists of a second format of fields, the first format of fields including a dynamic address translation (DAT) protection field (P), the second format of fields absent the DAT protection field;
• in response to an enhanced dynamic address translation (eDAT) facility being enabled, wherein translation table entries of the hierarchy of translation tables used in said dynamic address translation, other than the segment table entry, comprise DAT protection fields, determining whether said format control field in said segment table entry is enabled;
• and
• in response to said format control field being enabled, performing:
• obtaining from said segment table entry a segment-frame absolute address of a large block of main storage and a first DAT protection field;
• combining said obtained segment-frame absolute address with a page index portion of said virtual address and a byte index portion of said virtual address to form the translated address of the desired block of main storage within said large block of main storage, said desired block of main storage consisting of one or more bytes of data;
• determining whether any DAT protection fields in any translation table entries used in said performed dynamic address translation of said virtual address are enabled;
• and
• in response to all of said DAT protection fields being not enabled, permitting and store operations to said desired block of main storage in response to said store operations being associated with said performed address translation.