JPS6139142A - Main storage protection system - Google Patents

Abstract

PURPOSE:To prevent data in the memory area of a special storage key from being destroyed and to simplify programs by defining one of plural storage keys as the special storage key and setting part of the area in some program space with the special storage key. CONSTITUTION:Storage protection keys (storage) 0-15 are provided in correspondence to program spaces 1-15 of the main storage of the system, and one of those keys 0-15, i.e. key 0 is assigned as a privilege key to an operation system OS. Further, the keys 1-14 are assigned to the program spaces 1-14 individually and the remaining key 15 is defined as a data area protection key for memory data area protection. An important area required for prevention against data destruction in the program spaces 1-14 is set for the key 15 and the memory area is referred to. Further, when the area of the key 15 is updated, that is carried out with a specific instruction for indicating data movement and the constitution of the system and programs are simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a main memory protection method that facilitates prevention of data destruction on main memory in a computer system.

[Background of the invention]

In computer systems, in order to prevent data corruption in main memory, a memory protection key (storage key) is provided for each page of main memory, and when data on main memory is updated, the storage key of the page to be updated is The key is compared with the protection key (processor key) that indicates the execution state of the processor, and only when they match, the data of the corresponding page in the main memory can be updated. I have IIl & structure.

By the way, in conventional systems, one program (program space) is given one protection key, and memory is protected between it and other programs using a storage key or address space number. There is no memory protection key inside. Therefore, if you want to prevent data destruction for some important memory areas within the same program space, the storage key for that area can be omitted.
The privilege key (privileged mode) is equivalent to S (operation system). In this case, in order to update the privileged key area, a special 5VC (Super Viso
It is necessary to issue the rCa1l) command, which not only causes performance deterioration but also has the risk of destroying the OS area. Therefore, the actual situation is that the privileged key area is limited to important data that does not need to be updated.

On the other hand, in systems that handle important main memory data that is frequently updated and must be protected from destruction, the data update program performs processes such as sum checks to prevent data destruction. This has the disadvantage of complicating the processing of the data update program.

[Purpose of the invention]

The purpose of the present invention is to provide information on important data areas within the same program space without deteriorating performance or complicating processing.
An object of the present invention is to provide a main memory protection method that can easily prevent data destruction.

[Summary of the invention]

In the present invention, one of a plurality of storage keys is defined as a special storage key, and a part of the area in any program space can be set as a special storage key.

That is, within the same program space, memory areas with unique storage keys assigned to the space and memory areas with special storage keys coexist. Each program can refer to and update the memory area that has a unique storage key of the space, but the memory area that has a special storage key can only be read.
This prevents data from being destroyed in the memory area of the special storage key by making it impossible to update. The memory area of this special storage key is updated by a special command that instructs data transfer to the memory area.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the relationship between a program (program space) and a storage key according to the present invention. In FIG. 1, the protection key consists of 4 bits, and a total of 16 storage keys are assigned.

It is said that it can be done. Among these 16 storage keys, key 0 is assigned to O8 as a privileged key, and keys 1 to
14 are uniquely assigned to each program 1-14. The remaining key 15 is defined as a data area protection key (hereinafter referred to as data area key) for protecting the memory data area. This data
Area key 15 differs from keys 1 to 14 in that each program 1 to 14 uses data/data for some area within its space.
It can be set as an area key 15. That is,
Programs 1 to 14 set data area keys 15 for important memory data areas that require measures to prevent data destruction. The memory area with the effective data area key 15 can be referenced in the same way as the memory areas with keys 1 to 14 uniquely assigned to each program, but cannot be changed (written).

On the other hand, the program includes the following two instructions for updating the memory area having the data area key 15.

(1) 5ETDA (Set Data Area K
ey) Instruction Out of a plurality of main memory protection keys, the storage key specified by this instruction is recognized as a data area key, so the specified storage key is stored in the control register.

(2) WDA (Write Data Are
a) Data from the instruction non-data area key area.
W to move data to an area with an area key
A WDA instruction having a DA instruction is a type of data movement instruction in which a source data area address, a destination data area address, and a size of data to be moved are specified by the program.

The CPU determines whether the movement destination data area is an area that has a data area key stored in the control register with the 5ETDA instruction, and if it is an area that has a data area key, it is executed as a general data movement instruction. A similar operation is used to move data across keys.

FIG. 2 shows the operation of the CPU when it receives the 5ETDA instruction from the program. This indicates that the presence or absence of a storage protection mechanism using a data area key is verified, and if a storage protection mechanism exists, the storage key specified by the program is stored in the data area key control register. CC is a condition code that notifies the program of the instruction execution result.

Figure 3 shows the CPU when receiving the WDA command from the program.
shows the operation. The destination data area.

If the area has the same storage key as the data area key stored in the data area key control register, it performs the same operation as a general data movement instruction, and moves between areas with different storage keys. Indicates that data will be moved.

The error conditions in the figure are defined by checks in general data movement command processing.

In either the 5ETDA or WDA instruction, if there is an error in the specified information from the program, the condition code (CC) register notifies the program of the occurrence of an error condition, thereby terminating the instruction.

〔Effect of the invention〕

According to the present invention, an arbitrary memory data area that the program determines to be necessary can be set as a data area key in units of memory pages in units of programs (spaces), This makes it possible to protect the relevant data area from accidental data destruction due to program errors, and updates of the relevant data area can be executed in the same manner as general data movement commands, without degrading performance. can. Therefore, there is no need for data destruction prevention check processing using a data update program, which was conventionally required, and it is possible to easily improve system reliability without impairing performance.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the correspondence between programs and storage keys according to the present invention, and Figure 2 is a diagram showing the correspondence between programs and storage keys according to the present invention.
A diagram showing the PU operation, Figure 3 shows the CPU in the WDA instruction.
It is a figure which shows operation|movement.

Claims (2)

[Claims] (1) A memory protection key (hereinafter referred to as
A storage protection mechanism that provides a storage key (called a storage key), and when accessing main memory, compares the storage key of the corresponding area with the storage key assigned to the program, and if the two match, allows access to the corresponding area. In a computer system equipped with a special storage key, one of the multiple storage keys is defined as a special storage key and can be assigned to any program, and the area with the special storage key can only be accessed for reference. A main memory protection method characterized by: (2) The data in the area having the special storage key is updated by a specific instruction that instructs data movement from a non-special storage key area to the special storage key area. The main memory protection method described in scope 1.