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US 8,788,775 B2Granted
Memory access control using redundant and non-redundant encoding
AssigneeArm Limited
InventorRichard Roy Grisenthwaite
Life of this patent
Estimating the term…
Abstract
A data processing system 2 including processing circuitry 4 operating in either a first mode or a second mode. Page table data 30 including access control bits 40, 42, is used to control permissions for memory access to memory pages. In the first mode, the access control bits include at least one instance of a redundant encoding. In the second mode, the redundant encoding is removed to provide more efficient use of the access control bit encoding space.
Claims24
Apparatus for processing data comprising:
- processing circuitry responsive to program instructions to perform data processing operations and configured to operate in a plurality of modes;
- and
- memory management circuitry coupled to said processing circuitry and to a memory and configured to control access permissions to data values stored within said memory in dependence upon page table data;
- wherein
- said memory has a memory address space divided in to a plurality of memory pages and said page table data comprises a plurality of access control bits for each of said plurality of memory pages defining access permissions for a respective memory page;
- when said processing circuitry is in a first of said plurality of modes using a predetermined number of access control bits to encode access permissions, said memory management circuitry is responsive to at least one instance of a redundant encoding in which a plurality of different combinations of said access control bits provides a same set of access permissions;
- and
- when said processing circuitry is in a second of said plurality of modes using said predetermined number of access control bits to encode access permissions, said memory management circuitry is responsive to said plurality of different combinations of access control bits to provide a plurality of different sets of access permissions in a non-redundant encoding.
5 more elements
Apparatus for processing data comprising:
- processing means for performing data processing operations in response to program instructions, said processing means being configured to operate in a plurality of modes;
- and
- memory management means coupled to said processing means and to a memory for controlling access permissions to data values stored within said memory in dependence upon page table data;
- wherein
- said memory has a memory address space divided in to a plurality of memory pages and said page table data comprises a plurality of access control bits for each of said plurality of memory pages defining access permissions for a respective memory page;
- when said processing means is in a first of said plurality of modes using a predetermined number of access control bits to encode access permissions, said memory management means is responsive to at least one instance of a redundant encoding in which a plurality of different combinations of said access control bits provides a same set of access permissions;
- and
- when said processing means is in a second of said plurality of modes using said predetermined number of access control bits to encode access permissions, said memory management means is responsive said plurality of different combinations of access control bits to provide a plurality of different sets of access permissions in a non-redundant encoding.
5 more elements
A method of processing data comprising the steps of:
- performing data processing operations with processing circuitry in response to program instructions, said processing circuitry being configured to operate in a plurality of modes;
- and
- controlling access permissions to data values stored within said memory in dependence upon page table data;
- wherein
- said memory has a memory address space divided in to a plurality of memory pages and said page table data comprises a plurality of access control bits for each of said plurality of memory pages defining access permissions for a respective memory page;
- when said processing circuitry is in a first of said plurality of modes using a predetermined number of access control bits to encode access permissions, said access control bits provide to at least one instance of a redundant encoding in which a plurality of different combinations of said access control bits provides a same set of access permissions;
- and
- when said processing circuitry is in a second of said plurality of modes using said predetermined number of access control bits to encode access permissions, said plurality of different combinations of access control bits provide a plurality of different sets of access permissions in a non-redundant encoding.
5 more elements
Dependencies are inferred from the claim text.