System and method of controlling access to privilege partitioned address space for a model specific register file

• US 6,154,818 A
• Filed: 11/20/1997
• Issued: 11/28/2000
• Est. Priority Date: 11/20/1997
• Status: Expired due to Term

• Current Assignee: GlobalFoundries, Inc.
• Original Assignee: Advanced Micro Devices, Inc.
• Inventors: Christie, David S.
• Primary Examiner(s): Gossage, Glenn
• Application Number:
  US08/975,027
• Time in Patent Office: 1,104 Days
• Field of Search: 711/152, 711/163, 711/170, 711/153, 711/173, 712/200, 710/130
• US Class Current: 711/163
• CPC Class Codes: G06F 12/1491 in a hierarchical protection system, e.g. privilege levels, memory rings

Abstract

A system and method for controlling access to privilege partitioned address space for a model specific register file. A superscalar microprocessor includes a plurality of model specific registers (MSRs). MSRs differ between various implementations of a microprocessor architecture. The MSRs are allocated to access regions within a MSR file. Each access region of the MSR file is assigned access attributes. The MSRs are allocated such that the access region and the access attributes of the MSRs are defined by the address of the MSRs. Access to the MSRs is controlled by comparing the address of the MSR to the current privilege level of the microprocessor. In one embodiment, a validity check circuit is used to control access to the MSRs. If an access is attempted to a MSR that cannot be accessed at the current microprocessor privilege level, access to the register is denied and an exception is generated. In one embodiment, an address checker may be used to verify whether a MSR address is within a valid range. The MSR file may be divided into regions, with access granted based on a microprocessor being in a supervisory mode or a user mode.

Claims

1. A processor including an address space, the processor comprising:

one or more registers wherein each of said one or more registers is assigned to one of a plurality of access regions and each of said plurality of access regions is assigned a privilege level;

a validity check circuit configured to receive an address of a first register of said one or more registers, wherein said validity check circuit is configured to permit access to said first register if a privilege level input correlates to the privilege level assigned to the access region of that first register; and

wherein said one or more registers are model specific registers.

2. The processor as recited in claim 1, wherein said validity check circuit includes a remapper configured to map said address of said first register to a local address identifying said first register within said one or more registers.

3. The processor of claim 1, wherein said plurality of access regions comprise:

a first region including one or more registers that are only accessed when said privilege level corresponds to said processor being in a supervisory mode; and

a second region including one or more registers that are accessed when said privilege level corresponds to said processor being in a user mode.

4. The processor of claim 3, wherein said validity check circuit further comprises a read/write input configured to indicate whether data is being read from or written to said registers.

5. The processor of claim 4, wherein said plurality of access regions further comprise a third region including one or more registers that are written to only when said privilege level corresponds to said processor being in said supervisory mode and are read from when said privilege level corresponds to said processor being in said user mode.

6. The processor of claim 1, wherein addresses of each of said one or more registers identify which of plurality of said access regions correspond to each of said registers.

7. The processor of claim 6 wherein said validity check circuit includes an address checker configured to verify that said addresses are within a valid address range.

8. The processor of claim 6, wherein most significant bits of said address of said first register identify which of said plurality of access regions corresponds to said first register.

9. The processor as recited in claim 8, wherein first combination of said most significant bits identifies a first access region of said plurality of access regions, and wherein said first access region has a fixed set of access attributes.

10. The processor as recited in claim 9, wherein said fixed set of access attributes includes read and write access to said first register for a first privilege level and no access for a second privilege level.

11. The processor as recited in claim 9, wherein said fixed set of access attributes includes read access to said first register for a first privilege level and a second privilege level and write access for said first privilege level but not said second privilege level.

12. The processor as recited in claim 9, wherein said fixed set of access attributes includes read and write access to said first register for a first privilege level and a second privilege level.

13. A method of controlling access to registers in an address space of a computer system, the method comprising:

allocating registers to access regions of said address space, wherein each of said access regions is assigned a privilege level, and wherein said registers are model specific registers;

receiving a privilege level input;

receiving an address of a register, wherein said address identifies an access region to which said register is allocated;

comparing said privilege level assigned to said access region identified by said address of said register to said privilege level input; and

accessing said register if said privilege level assigned to said access region identified by said address of said register correlates to said privilege level input, wherein said register is a model specific register.

14. The method as recited in claim 13 further comprising receiving a read/write signal that indicates whether data is being written to or read from said registers.

15. The method as recited in claim 13 further comprising comparing said address to a valid address range.

16. The method as recited in claim 13 wherein said privilege levels include:

a first level wherein access is permitted only when said privilege level input corresponds to said processor being in a supervisory mode; and

a second level wherein access is permitted to a user when said privilege level input corresponds to said processor being in a user mode.

17. The method as recited in claim 13 further comprising mapping said address of said register to a local address identifying said register within said registers.

18. The method as recited in claim 13 wherein most significant bits of said address identify said access region and said privilege level.

19. The method as recited in claim 18, wherein a first combination of said most significant bits identifies a first access region of said plurality of access regions, and wherein said first access region has a fixed set of access attributes.

20. The method as recited in claim 19, wherein said fixed set of access attributes includes read and write access to said register for a first privilege level and no access for a second privilege level.

21. The method as recited in claim 19, wherein said fixed set of access attributes includes read access to said register for a first privilege level and a second privilege level and write access for said first privilege level but not said second privilege level.

22. The method as recited in claim 19, wherein said fixed set of access attributes includes read and write access to said register for a first privilege level and a second privilege level.

23. A computer system comprising:

a microprocessor wherein said microprocessor includes;

one or more registers wherein each of said one or more registers is assigned to one of a plurality of access regions and each of said plurality of access regions is assigned a privilege level;

a validity check circuit configured to receive an address of a first register of said one or more registers, wherein said validity check circuit is configured to permit access to said first register if a privilege level input correlates to the privilege level assigned to the access region of that first register, wherein said registers are model specific registers;

a bus bridge coupled to said microprocessor;

a main memory coupled to said microprocessor; and

an input/output device coupled to said bus bridge.

24. The computer system of claim 23 wherein said plurality of access regions comprise:

a first region including one or more registers that are only accessed when said microprocessor is in a supervisory mode; and

a second region including one or more registers that are accessed when said microprocessor is in a user mode.

25. The computer system as recited in claim 23, wherein said validity check circuit includes a remapper configured to map said address of said first register to a local address identifying said first register within said one or more registers.

26. The computer system of claim 23 wherein addresses of said registers identify said access regions of said registers.

27. The computer system of claim 26, wherein said validity check circuit includes an address checker configured to verify said addresses are within a valid address range.

28. The computer system of claim 26 wherein most significant bits of said addresses identify said access regions.

29. The computer system as recited in claim 28, wherein a first combination of said most significant bits identifies a first access region of said plurality of access regions, and wherein said first access region has a fixed set of access attributes.

30. The computer system as recited in claim 29, wherein said fixed set of access attributes includes read and write access to said first register for a first privilege level and no access for a second privilege level.

31. The computer system as recited in claim 29, wherein said fixed set of access attributes includes read access to said first register for a first privilege level and a second privilege level and write access for said first privilege level but not said second privilege level.

32. The computer system as recited in claim 29, wherein said fixed set of access attributes includes read and write access to said first register for a first privilege level and a second privilege level.