JPH03148735A - Memory managing device - Google Patents

Abstract

PURPOSE:To reduce the overhead of an operating system (OS) by providing a mode unchanged flag on every specified area of a virtual space so that a memory protection exception processing can be executed while maintaining the traveling mode of a CPU at a non-priviledge mode when the flag shows a mode unchange. CONSTITUTION:On every specified area of the virtual space, the mode unchanged flag is provided to show whether the memory protection exception processing is executed by the priviledge mode or the non-priviledge mode of a CPU 5. When memory protection exception is detected by a memory protection exception detecting means 3, a mode unchanged flag deciding means 4 refers to the mode unchanged flag and when the memory protection exception processing in the non-priviledge mode is instructed, a mode unchanged informing signal 9 is formed of the CPU 5. Thus, since the CPU 5 executes the memory protection exception processing while maintaining the non-priviledge mode, when the traveling mode of the CPU is changed from the non-priviledge mode to the priviledge mode, the overhead of the OS can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a memory management device, and particularly to an application program (hereinafter abbreviated as AP) running in a non-privileged mode of a central processing unit below (hereinafter abbreviated as CPU). )
Detects that an illegal reference (hereinafter referred to as a memory protection exception) has occurred when the user references a virtual space that is not allowed to reference, and sends the CP to a preset address.
The present invention relates to a memory management device that transfers control of U to perform specific processing (hereinafter referred to as memory protection exception processing).

[Conventional technology]

Conventionally, this type of memory management device notifies the CPU of the occurrence of a memory protection exception when a memory protection exception caused by an AP running in a non-privileged mode of the CPU is detected.
Upon receiving this notification, the PU switched the running mode from non-privileged mode to privileged mode, moved allm to a preset address, and executed memory protection exception handling.

In this way, switching the CPU running mode from non-privileged code to privileged mode when a memory protection exception occurs is as follows:
Memory protection exceptions usually occur when the AP refers to an address that it should not originally refer to, so it is the responsibility of the operating system (hereinafter abbreviated as OS) to detect and handle this. It is.

By the way, the OS generally provides a means for multiple APs to allocate the same 911111 space to their own virtual space and share the physical space. In such an OS, when a certain API and AP2 share a physical space, a mechanism is realized in which AP2 can detect, for example, that an API has written to a virtual space to which the same physical space is allocated. If you try to do this, first remove the R1i right to write to the virtual space that is allocated to the same physical space of the API, and then
When an exception occurs, a procedure is required in which the OS notifies the AP 2 that writing has occurred.

For details, when using a conventional memory management device, the API
Drop (turn off) the page reference flag indicating whether writing is possible in the page table of the virtual space to which the same physical space of AP2 is allocated and the virtual space to which the same physical space of AP2 is allocated. Ok, API
A memory protection exception that occurs when one of AP2 and AP2 writes in a virtual space to which the physical space of -1 is allocated is notified to the other AP during memory protection exception processing.

However, writing to the virtual space by intentionally dropping the page reference flag is originally a legitimate write (not a write to an invalid area), and the frequency of writing is high. However, if the CPU running mode was switched from non-privileged mode to privileged mode when a memory protection exception occurred, every time the API references a virtual space allocated to the same physical space, the CPU
Not only is it necessary to switch the running mode of the CPU, but also the running mode of the CPU must be switched from privileged mode to non-privileged mode again at the end of memory protection exception handling, which increases the overhead of the OS.

[Problem to be solved by the invention]

In the conventional memory management device described above, the CPU running mode was switched from non-privileged mode to privileged mode every time a memory protection exception occurred. This increases the overhead of the OS, and it also becomes necessary to switch the running mode of the CPU from privileged mode back to non-privileged mode, which also increases the overhead of the OS.

In view of the above-mentioned points, an object of the present invention is to provide a mode unchanged flag for each specific area of a virtual space, and determine whether the mode unchanged flag indicates mode unchanged when a memory protection exception occurs. An object of the present invention is to provide a memory management device which performs memory protection exception handling while the running mode of a CPU remains in a non-privileged mode when the mode is not changed.

[Means for Solving the Problems] The memory management device of the present invention has an address translation mechanism that allocates a physical address of a storage device to a virtual space that is an address space recognized by a CPU, and runs in a non-privileged mode of the CPU. A memory protection exception detection means detects that a memory protection exception occurs when an application program references a virtual space that is not permitted to reference, and transfers CPU control to a preset address to handle the memory protection exception. In a memory management device that performs
A mode unchanged flag indicating whether memory protection exception handling is to be executed in privileged mode or non-privileged mode of the CPU for each specific area of the virtual space, and when a memory protection exception is detected by the memory protection exception detection means. and a mode unchanged flag determination means that refers to the mode unchanged flag and suppresses switching of the CPU from the non-privileged mode to the privileged mode if memory protection exception handling in the non-privileged mode is instructed.

[Effect]

In the memory management device of the present invention, the mode unchanged flag indicates whether memory protection exception handling is to be executed in a privileged mode or a non-privileged mode of the CPU for each specific area of the virtual space, and the mode unchanged flag determination means When a memory protection exception is detected by the memory protection exception detection means, the mode unchanged flag is referenced and if memory protection exception handling in non-privileged mode is instructed, the CPU is switched from non-privileged mode to privileged mode. suppress.

〔Example〕

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a memory management device according to an embodiment of the present invention. The memory management device 1 of this embodiment includes an address translation mechanism 2, a memory protection exception detection means 3, and a mode unchanged flag determination means 4.

The address conversion 11tiz converts the virtual address 6 output from the CPU 5 into a physical address.

The memory protection exception detection means 3 monitors the occurrence of a memory protection exception in the address change aa structure 2, and sends a memory protection exception notification signal 8 to the CPU 5 when a memory protection exception is detected.
to notify.

The mode unchanged flag determination means 4 detects the mode unchanged flag 11a (see FIG. 2) in the address translation mechanism 2 when the memory protection exception detection means 3 detects a memory protection exception.
Refer to , when the mode unchanged flag lla is on (
(When memory protection exception processing in non-privileged mode is instructed), a mode unchanged notification signal 9 is notified to the CPU.

When the CPU receives the memory protection exception notification signal 8 but does not receive the mode no change notification signal 9, it switches the running mode from the non-privileged mode to the privileged mode, transfers control to a preset address, and protects the memory. Execute exception handling in privileged mode. Furthermore, when the CPU receives the mode no change notification signal 9, it suppresses the switching of the running mode from the non-privileged mode to the privileged mode despite receiving the memory protection exception notification signal 8, and Transfers WA control to the address and executes memory protection exception handling in non-privileged mode.

FIG. 2 is a diagram for explaining an overview of address translation by the address translation mechanism 2. As shown in FIG. Address conversion mechanism 2 uses area table 10- and page table 20 to convert virtual address 6 to physical address, and converts area table 1G and page table 20 using the decomposed values of virtual address 6. is referring to. That is, the address translation mechanism 2 recognizes the virtual address 6 by decomposing it into an area table entry determination field 6a, a page table entry determination field 6b, and an intra-page offset determination field 6c.

The area table IO is composed of a plurality of area table entries 11, and one area table entry 11 is designated by the value of the area table entry determination field 6a of the virtual address 6. A mode unchanged flag lla is provided which indicates whether memory protection exception handling is to be performed in the privileged mode or non-privileged mode of the CPU 5 when an exception occurs.

The page table 20 is composed of a plurality of page table entries 21, and one page table entry 21 is designated by the value of the page table entry determination field 6b of the virtual address 6.

The page table entry 21 is provided with a page reference right flag 21a that indicates whether or not the physical page 41 in the physical space 40 can be referenced.

In the example of FIG. 2, three flags, read, write, and execute, are provided as the page reference flag 21a.

Next, the operation of the memory management device of this embodiment configured as described above will be explained.

When a certain AP refers to the virtual address 6 of a page that is allowed to refer to the virtual space (the page reference flag 12 is on), the virtual address 6 output from the CPU is address translation mechanism 2
The address is translated into a physical address by

Specifically, the address translation mechanism 2 first converts the virtual address 6
Select one area table entry 11 in the area table 10 using the area table entry determination field 6a of the address change! The negative mechanism 2 is the page table 20 in the selected area table entry ll.
, and the page table entry determination field 6b of the virtual address 6.
Finally, the address translation mechanism 2 selects one of the page table entries 21 in the selected page table entry 21, and calculates the number of the physical page 41 in the physical address in the selected page table entry 21 and the intra-page offset determination field 6C of the virtual address 6.
is used to determine the physical address in the IkTl page 41 of the physical space 40.

While the address translation mechanism 2 is converting the virtual address 6 output from the CPU, the memory protection exception detection means 3 refers to the page reference right flag 21a of the page table entry 21 to determine which virtual address 6 is valid. Check whether or not. If the virtual address 6 is valid, the address translation mechanism 2 outputs the physical address.

As a result, the physical memory of the storage device is referenced.

On the other hand, a certain AP is not allowed to reference the virtual space (
When the virtual address 6 of a page (the page reference right flag 21a is not on) is referenced, the memory protection exception detection means 3 teeth,
Page reference right flag 21 of page table entry 21
A is referenced to check whether it is a valid virtual address 6, and since it is an invalid virtual address 6 that is not allowed to be referenced, it is detected that a memory protection exception has occurred, and the CPU 5
A memory protection exception notification signal 8 is output to the memory protection exception notification signal 8.

Further, when the memory protection exception detection means 3 detects the occurrence of a memory protection exception, the mode unchanged flag determination means 4 refers to the mode unchanged flag tta of the area table end entry l l and determines the running mode of the CPU 5. The CPU determines whether to switch from a non-privileged mode to a privileged mode, and does not output a mode change notification signal 9 to the CPU 5 when switching the running mode of the CPU 5 is instructed. Therefore, the CPU sends a memory protection exception notification 13 No. 8
In response to this, the running mode is switched from non-privileged mode to privileged mode, and then control is transferred to a preset address and memory protection exception handling is executed in privileged mode.

On the other hand, when switching the driving mode of the CPLJ 5 is not instructed by referring to the mode unchanged flag lla of the area table entry 11, the mode unchanged flag determining means 4 outputs a mode unchanged notification signal 9 to the CPU. Therefore, despite receiving the memory protection exception notification signal 8, the CPU transfers control to a preset address without changing the running mode and executes memory protection exception handling in a non-privileged mode.

In this way, when an AP running in unprivileged mode causes a memory protection exception, the mode unchanged flag ll
Memory protection exception handling can be selectively executed in non-privileged mode depending on whether a is turned on or off.

Referring to FIG. 3, API and AP2 allocate the same physical space 32 to their respective virtual spaces 34 and 35. For example, suppose that the OS attempts to provide a mechanism for the API and AP2 to detect that the other party has written to the virtual space 34 or the virtual space 35.

When using the memory management device l of this embodiment, the AP
The same physical space 37 is allocated to the communication areas 36 and 38 of the virtual space 31 of I and the virtual space 33 of AI2, and the page reference right flag 21a of the corresponding page table entry 21 is turned off. If the mode unchanged flag l1m of table entry 11 is turned on (and, for example, if the API
When writing to , a memory protection exception is detected, but the CPU running mode is not switched.
Since memory protection exception handling is performed in non-privileged mode, write that a memory protection exception has occurred in the 1ε area 36 during the memory protection exception handling (then, the AP
2 can know that the API has written to the virtual space 34 by looking at the communication area 38 when it starts its operation. In this way, API virtual space 3
Since switching of the CPU running mode does not occur when writing to 4, OS overheft can be minimized.

In the above embodiment, the case where the mode unchanged flag lla is provided in the area table entry 11 for each area of the virtual space has been described, but the mode unchanged flag is set for each page of the virtual space. It goes without saying that the present invention can be similarly applied even if it is provided in the table entry 21.

[Effect of the Invention J As explained above, the present invention provides a mode unchanged flag for each specific area of the virtual space, and when a memory protection exception occurs, the mode unchanged flag determining means determines whether the mode is unchanged. If the mode is unchanged, the CPU
By performing memory protection exception handling while keeping the running mode of the CPU in non-privileged mode, it is possible to reduce the OS overhead caused by changing the running mode of the CPU from non-privileged mode to privileged mode, and also to avoid memory protection. This has the effect that the overhead of the OS for returning the CPU running mode from the privileged mode to the non-privileged mode at the end of exception handling can also be reduced.

[Brief explanation of the drawing]

1 is a block diagram showing the configuration of a memory management device according to an embodiment of the present invention; FIG. 2 is a diagram for explaining address conversion by the 7-address conversion mechanism in FIG. 1; different AP
FIG. 3 is a diagram illustrating an example in which two devices share the same physical space. In the figure, l...Memory management device, 2...Address translation mechanism, 3...Memory protection exception detection means, 4...Mode unchanged flag determination means, 5...CPU
. 6...Virtual 7 dress, 6a...Area table entry determination field, 6b...Page table entry determination field, 6C...Intra-page offcent determination field, 7...
Physical address, 8...Memory protection exception notification signal, 9...Mode unchanged notification signal, lO...Area table, 11...Area table entry, tta-Mode unchanged flag, 20...Page table, 21 ...Page table entry, 21a.Page reference right flag, 40..Physical space, 41..Physical page.

Claims (1)

[Claims] A virtual space that has an address conversion mechanism that allocates the physical address of a storage device to a virtual space that is an address space recognized by the CPU, and that application programs running in the non-privileged mode of the CPU are not permitted to reference. In a memory management device, a memory protection exception detection means detects that a memory protection exception has occurred when a memory protection exception has occurred, and transfers control of the CPU to a preset address to perform memory protection exception handling. A mode unchanged flag indicating whether memory protection exception handling is to be executed in privileged mode or non-privileged mode of the CPU for each specific area, and a mode change flag indicating whether memory protection exception handling is to be executed in privileged mode or non-privileged mode of the CPU, and when a memory protection exception is detected by the memory protection exception detection means, the mode The present invention is characterized by comprising mode unchanged flag determining means that refers to the unchanged flag and suppresses switching of the CPU from the non-privileged mode to the privileged mode if memory protection exception handling in the non-privileged mode is instructed. Memory management device.