DE10127186A1 - Computer system with virtual addressing has a hardware unit within the memory management unit for controlling access to physical memory, so that the computer itself can use virtual memory addresses - Google Patents

Abstract

Computer system with virtual addressing comprises a read only memory (12, 14) for storage of imaging rules with which virtual addresses are allocated to physical addresses in a unique manner. The computer system further comprises a hardware condition machine that can access ROM in order to determine the physical memory addresses from the imaging rules and the virtual addresses. As the hardware condition machine accesses the physical memory the computer system itself can be initialized and addressed using virtual memory addresses. An Independent claim is made for a method for determining physical addresses from virtual addresses.

Description

The present invention relates to computer systems and especially on computer systems with virtual addressing tion.

Virtual addressing has long been out of the field of the workstations known. Using a specific one Mapping instructions are virtual addresses on physi addresses shown. The physical addresses adres Sieren memory cells of a physical memory, such as. B. the RAM, a hard drive, a tape player chers etc. Virtual addresses do not refer directly on physical memory cells, but only indirectly, about the mapping rule. The advantage of this address Type of development consists in the fact that the programmer not about the existing di in a computer system verse physical memory must take care of. The programmer has a virtual address space that he can use for can use his program as needed. The figure on the physical address space that a special computer system system, it is separated from the program code provides so that by providing different images regulations a pro programmed with virtual addresses gram can run on different computer systems.

In the technical publication "Protected Virtual Memory - 32- Bit power without handbrake on ", Stephan Ondrusch, 10. GMD SmartCard Workshop, Darmstadt, February 9, 2000, will be the Advantages of virtual addressing for chip cards wrote. In smart cards on which various applications should run, which are separated from each other for security reasons should be separated, each process or task is an egg  Gener provided virtual address space, which at Creation of the program code for the process defined and dated Operating system is set up at runtime. Under the con trolls of the operating system of the chip card are access rights te on additional chip resources, e.g. B. shared Spei areas, registered and constantly monitored by hardware. This makes it possible to set up the program codes for two processes to create a chip card independently of one another by two separate virtual address spaces are available be made available. Through the mapping rules for the two virtual address spaces on the only available NEN physical address space can be ensured that the two processes do not interfere or that the two Processes control a physical memory area share, for example, certain routines to use together, so these routines only one Times must be stored in the memory of the chip card sen, or to secure data exchange between the Pro to achieve zessen.

Running in a processor with a virtual memory system an application in the so-called virtual address space from. Any address of the virtual memory, from which the application read / write data or executable code is based on an address in physical memory formed on which this data or code actually ge stores are. The virtual address (VA) and the via the Figure specification assigned physical address (PA) don't have to have any relation to each other. The virtual ad The space can also be much larger than the physical one Address space.

Virtual addresses where there are no readable / writable data or executable code are usually not mapped to physical storage. For the executed application, this image is completely transparent rent.  

When organizing the memory in Pages or Pages is the virtual address space in the same size, overlap-free Divided memory area. A page in the virtual address space is a page in the physical address space about the Ab assigned education instruction, the page in physi The address space is also known as a page frame.

The user data memory of a page frame of the physical Address space is the same size as that of a page of the virtual len address space.

The assignment of a virtual page to a physical one Page is usually via the so-called page table or Page Table reaches which address pairs of each Start addresses of the virtual pages and the assigned phy contains physical pages.

For workstations, part of the page table is in egg cache, which is also known as a "Translation Look Aside Buffer (TLB) referred to as. The start address pair is for one virtual page and the assigned physical page in the TLB, the address mapping is calculated in the accelerated virtual memory area because only one Access to a table is required to match a vir to obtain the physical address assigned to the current address th.

Is the start address pair, i. H. the virtual address se and the assigned physical address, not in the TLB, so a TLB miss occurs, which is more common wise leads to a trap to the operating system, which the Must add the address tuple in the TLB.

In the area of the workstations, the mapping rule between virtual address space and physical address space, which, for example, implements as a single page table  can be kept in volatile memory. When a Workstation is started, it starts in real addressing mode. This means that the operating system of the workstation causes the CPU of the workstation to real, d. H. physical addressing mode in which volatile memory of the workstation a page table build up little by little. Only when a page table is structured, the workstation can be found in the virtual addresses Switch mode. The CPU then requests data a virtual address, so in the fleeting workspace the physical address of the CPU to retrieve the data from the memory. Übli Che workstations are characterized in that they are in in a real addressing mode and then when the Mapping rule from the virtual address space to the physical address space in volatile memory switch to virtual addressing mode.

One disadvantage of this concept is the fact that a relatively large amount of memory is needed to to save a page table. This disadvantage is for work stations not of paramount importance as they are very large men of memory. For other users applications such as B. for security-relevant computer systems, such as those implemented in chip card ICs, the storage resources are available due to the low limited space. Providing a Amount of volatile memory to create a page table save, leads to the fact that the executed on the chip card Applications may have insufficient memory and thus experience a loss of performance.

Another disadvantage of the known concept is that that a significant administrative effort is required to next, when starting up the computer system, the page table build up, d. H. from stored information gradually after calculating and saving the address assignments.  

In addition to the fact that it requires computing resources corresponding programs must also be on a chip card be provided to those for virtual addressing necessary precautions. Also sol che programs need storage space, for space reasons especially with smart cards or other security ICs is rare good.

Another disadvantage of the Initia concept described in physical addressing mode and on it following switching to virtual addressing mode is that the advantages of virtual addressing mode, i.e. the separation of two Ap to be separated from each other complications, not received from the start, but only when the CPU has ended the real mode and in switched the virtual addressing mode. A phy sical addressing mode or a "real" address The control mode is particularly important for safety controllers is a security weakness, also known as the "single point of Attack ". If an attacker succeeds in Operating system of the smart card IC to penetrate while the same is in physical addressing mode, so the attacker can use physical barriers without barriers Access memory cells and read sensitive data or something even manipulate. The security features of the virtual ad Resource modes are therefore not reached from the beginning, but only when the computer system in the virtual Has switched addressing mode.

The object of the present invention is a si to create a more secure and simple computer system.

This task is performed by a computer system with a virtual ad ressierung according to claim 1 and by a method for Get a physical address from a virtual one Address solved according to claim 17.  

The present invention is based on the finding that that the security of a computer system with virtual ad Resessierung can be improved in that the calculator system does not use a physical addressing mode, but from the outset ar in the virtual addressing mode beitet. To accomplish this is done in a non-volatile Memory of the computer system abge a mapping rule saves a phy from a virtual address sical address can be determined. The illustration before scripture is stored in the non-volatile memory, so that the same immediately when starting up the computer system is and not only in one, as in the prior art real mode generated and stored in volatile memory must become. This also means the complete administrative effort and the programs required to make an illustration regulation, for example in the form of a hash table testify, lapsed, since the illustration rule already in non-volatile memory is readily available.

So that the computer system is already in virtual addressing According to the invention, in addition to the non- volatile memory in which the mapping rule is saved chert, a hardware state machine is provided on can access and trained the non-volatile memory is to use the virtual address and the Ab Educational instruction assigned to the virtual address determine physical address. The hardware- State machine performs, as is usual with state machines is, a predefined algorithm automatically from where at the algorithm that the hardware state machine is made of leads, on the one hand, input data from the non-volatile Receives memory and on the other hand the virtual address as Input data, the physical address as output data issue.

The simplest way, but not the best way and way is to create a complete page table in the non-  to store volatile memory. In this case, the Hardware state machine can be activated when the CPU of the Computer system requests data at a virtual address. In this case, the hardware state machine becomes the virtu Read the address into the non-volatile memory access the physical address that the virtual ad resse is assigned, extract from the page table and then output.

However, for reasons of efficiency and storage space, it will be before trains the mapping rule in the form of a hierarchical Baums with a root node for a root level, at least an intermediate node for at least one intermediate level and egg nem end node for an end level so that the Hardware state machine, controlled by the virtual ad and from stored in the non-volatile memory lists for the individual nodes a so-called page Table Walk ("Table Walk") performs to Passing through the tree to output the physical address that corresponds to the entered virtual address. At a preferred embodiment of the present invention, where the virtual address space is much larger than that is physical address space, and thus lists for nodes relatively few entries used and a relatively large number Have zero entries, the lists for nodes of the hierarchical tree compressed to save space in the non- to save volatile memory.

In the case of such a hierarchically organized mapping regulation between virtual and physical address must not the whole picture regulation in the non-volatile Memory can be saved, but at least part of it Illustration rule by which it is possible to make a high to start driving the system in virtual mode. at it is then suitable list entries in virtual mode possible, already when recovering the required data the physical memory in the volatile working memory  to generate the remaining part of the mapping rule and for further address translations from virtual to physical too use. The hardware state machine can therefore according to the Starting up the system in virtual mode is also possible Data programmed in volatile memory at runtime access.

In a preferred embodiment of the present The invention is also a page addressing before Trains t. To avoid memory fragmentation, in In this case, as much as possible combined lists in one and same physical page.

An advantage of the present invention is that Computer system only a virtual addressing and no ne can perform physical addressing, and the Si security weakness is no longer present.

Another advantage of the present invention is in that no programs or no administrative effort are required is necessary to create a page table in the volatile memory as the page table or the hierarchical tree in the non-volatile memory is stored persistently.

Another advantage of the present invention is in that in the case of the mapping rule as hierarchical Tree structure by implementing access rights to the Node of the tree a differentiated access rights assignment can be achieved with an adjustable granularity.

Another advantage of the present invention is in that by saving the mapping rule in the non- volatile memory, in a form such as that of the Hardware state machine used without switching on the CPU CPU resources can be saved. Selbstverständ Lich the mapping rule, for example the page  Table or the hierarchical structure of node lists be put. However, this can be outside of the operation of the Computer system to a certain extent "off-line" or in the case of one Chip card "Off-Card" are carried out. Creating the Mapping rule and saving the mapping rule Writing in the non-volatile memory is therefore of no value full online resource of memory or CPU, but can, if there is enough time, for example at the Production of the chip card or in the case of a dynamic mo then the mapping rule can be made if the computer system has no security-relevant access application. According to the invention can therefore machining steps from online operations for valuable online resources such as B. Computer track free space, storage space, energy consumption etc. or save.

Preferred embodiments of the present invention are referred to below with reference to the attached drawing explained in detail. Show it:

Fig. 1 shows an inventive computer system having virtual addressing;

Fig. 2 is a schematic representation of an image of a virtual address space into a physical Ad ressraum for a computer system on a chip card;

Fig. 3 is a block diagram of an address translation using a page table;

Fig. 4a is a schematic representation of an address translation using a mapping rule in the form of a hierarchical tree structure;

FIG. 4b is a table showing the nodal planes and the addressed by a node address ranges according to a preferred embodiment of the present invention;

Fig. 5 is an example of a mapping rule in the form of a hierarchical tree structure can be skipped schenk sheet in the interim;

FIG. 6 shows a table for representing node sizes at different levels for the example of FIG. 4a;

Figure 7 is an example of a mapping rule in the form of an n-tree with the same sizes for additional nodes one level.

Fig. 8 is a schematic representation of a compression method for node lists to improve the ratio of entries used to the total number of entries in a list;

Fig. 9 compression examples according to the compression process of Fig. 8;

Fig. 10 is a compressed representation of the tree of Fig. 7;

FIG. 11 shows a storage space-optimized storage of the tree from FIG. 10; and

Fig. 12, is to refer to a physical address stored in a node list, a representation of a virtual address that is difiziert mo.

Fig. 1 shows an inventive computer system having a CPU 10, a nonvolatile memory in the form of a ROM 12 and an E ² PROM 14 shows, referred to in Fig. 1 as an NVM (non volatile memory NVM). The computer system can also ner a volatile memory 16 , which is designated in FIG. 1 with RAM, and, if appropriate, further peripheral components, such as, for. B. include a coprocessor, an input / output interface, a random number generator, etc.

The computer system further includes a Speicherverwaltungsein unit (MMU; MMU = Memory Management Unit) 18 and a cache 20, the cache 20 in an instruction cache and a data cache may be divided, if the computer system accelerator as the Harvard architecture is constructed. The CPU is connected to the memory management unit 18 via a virtual address bus 22 . The memory management unit 18 comprises a hardware state machine 18 a and preferably a translation look-aside buffer (TLB) 18 b in order to determine a physical address from a virtual address supplied by the CPU 10 via the bus 22 , by which a virtual address To address the assigned address data from a memory 12 , 14 , 16 and to load it via a data / command bus 24 into the cache 20 , from which the CPU 10 assigns a virtual address via a further command / data bus 26 Receives data.

From Fig. 1 it can also be seen that the hardware state machine 18 a of the memory management unit 18 can access a non-volatile memory in the form of the ROM 12 or the NVM 14 via an access bus 26 to the Abbil extension rule that is used to calculate the physical Addresses from the virtual address is required to load from the non-volatile memory. The hardware state machine 18 a can thus access the non-volatile memory via the access bus 26 in order to determine the physical address assigned to the virtual address using a virtual address and the mapping rule stored in the non-volatile memory.

From Fig. 1 it can be seen that the CPU 10 preferably addresses exclusively via the virtual address bus 22 , in particular the hardware state machine 18 a addresses, which according to the invention can directly access the non-volatile memory, so that the computer system according to the invention no physical addressing mode required, but can start up in virtual addressing mode, so that there is no point of attack in the form of an operating system running in physical addressing mode of the computer system according to the invention.

In the following, virtual storage systems are discussed in general. A protective mechanism for multitasking computer systems is that separate processes or applications are assigned separate virtual address spaces, so that multitasking operation with various applications is possible, but these applications must be completely separated from one another for security reasons. In a preferred embodiment of the computer system according to the invention, which is suitable for a chip card, a virtual address space of 4 gigabytes is provided, as can be seen in FIG. 2. For reasons of better efficiency, the address space is divided into virtual memory pages 30 , a memory page having a size of 64 bytes, that is to say 512 bits. The memory pages of the virtual address space can be addressed using a 32-bit wide virtual address.

It is essential in the concept of virtual addressing that an application that runs on the CPU cannot directly access the physical memory, but only its own virtual address space. Using the memory management unit 18 of FIG. 1, the virtual address space is mapped into physical memory addresses using a mapping rule 32 , which is symbolized by the arrows shown in FIG. 2. In the embodiment shown in Fig. 2, the physical address space is set to 4 MB, but it should be noted that a conventional chip card has far less memory. Typical memory sizes for the E ² PROM 14 of FIG. 1 are 64 kbytes. The RAM 16 of FIG. 1 is typically 8 Kbytes, while the ROM 12 of FIG. 1 is typically 168 Kbytes. If a virtual address space of 4 GB is mapped to approximately 240 kbyte memory cells, it can be seen that a large amount of virtual addresses does not first have to be mapped into physical memory addresses, and that, in addition, a large number of physical memory addresses do not actually exist show physical memory cells. On the other hand, the overdimensioning of the virtual address space compared to the physical address space and the overdimensioning of the physical address space with respect to the actually existing memory cells allow simple modifications in that additional che memory can be easily inserted later or that the physical address space is necessary speed can be expanded.

As will be explained later, the Abbil extension 32 according to the invention is not built up by the CPU in RAM 16 , but developed for example during the manufacture of the chip card and programmed in the ROM 12 in the form of an appropriately designed ROM mask before the inventions computer system according to the invention is put into operation. In operation, apart from the state machine, the computer system therefore does not require any resources to generate the mapping rule 32 . The steps required for this have already been carried out off-line in order not to have to use up valuable on-line capacities of the computer system.

A virtual address is in a corresponding physical rule's z. B. translated using a translation table le, commonly referred to as a page table. The page table can be organized in the form of a single table which has entries, each entry comprising a virtual address and the physical address assigned to it. As will be explained later, however, it is preferred according to the present invention to organize the mapping rule in the form of a hierarchical page assignment tree. A mapping rule organized in this way has the advantage of greater flexibility for managing access rights. It is also more suitable for handling small page sizes, which is important when the computer system is used as a security IC in a chip card. Small page sizes, e.g. B. less than or equal to 256 bytes, also serve to avoid page table fragmentation. A memory page therefore has, as has been explained with reference to FIG . B. a size of 64 bytes, ie 512 bits. This means that the page offset must be 6 bits long in order to be able to address the 64 bytes starting from the start address for the page.

In the following, reference is made to FIG. 3. Fig. 3 shows a schematic representation of an address translation using a page table. A virtual address 30 , an AMO field 32 and a TID field 34 are used as input. The AMO field 32 denotes the access mode which is set by the current state of the CPU and the intended access type (read, write, execute, etc.). The TID field 34 is required for multitasking operation and provides a task identifier (Task I dentifier), which indicates which task the virtual address 30 is assigned to in order to differentiate between different virtual address spaces of different applications. The so-called extended virtual address is obtained from the virtual address 30 and the TID field 34 , which has the start address for the virtual page (VP 36 ) and an offset value (DP 38 ).

The assignment rule in the form of a page table 40 comprises various entries, each entry having a column 42 for the start address of the virtual page and a column 44 for the start address of the physical page which is assigned to the virtual page in column 42 . According to a preferred exemplary embodiment of the present invention, the page table further comprises a column 46 for access rights (EAR = EAR = Effective Access Rights), wherein a rights module 48 is used to check whether the CPU mode defined by the AMO field 32 has access to it has a virtual address with a specific EAR field. If it is determined that the CPU has no access to a virtual address, the address translation is refused and an access violation is issued. Therefore, since the access rights check takes place before the address translation, that is to say in the virtual address space, the CPU cannot even get the physical address, let alone the content of the memory cell addressed by the physical address. An associative search is carried out in the page table in order to provide the mapping of the virtual address to the physical address. The virtual address in the page table must match the field 36 of the expanded virtual address. If no such entry is found in the page table, a page fault is output by a module 50 . If, on the other hand, a suitable entry is found, the physical page address is read from column 44 . In a preferred embodiment of the present invention, a virtual page is exactly the same size as a physical page, and the offset of the virtual address (DP 38 ) and the offset 52 of the physical address are the same, so that no offset values are stored in the page table or special processing of offset values is necessary.

As has already been explained with reference to FIG. 1, the memory processing unit 18 preferably comprises a TLB in order to achieve faster addressing. The page table described with reference to FIG. 3 is held in the TLB according to a preferred embodiment of the present invention, the TLB optionally being present in addition to the hardware state machine 18 a. The TLB is designed in the form of the cache table shown in FIG. 3 and comprises a list of virtual addresses with corresponding physical addresses for quick access. The TLB is filled with the last used address pairs and can be updated either randomly or according to time. One possibility, for example, is that as soon as the TLB is filled up and a new entry is to be added, the oldest entry is deleted in order to make room for a new entry. The size of the TLB is a hardware factor and can therefore be selected specifically depending on the design.

Are the hardware resources for example due to the be necessary chip space, the TLB is not all be large, and the hardware state machine will be activated more often, while in other cases, at where the TLB can be kept very large, the hardware State machine is only active at the beginning when the TLB, which is a volatile buffer, is still empty after the TLB and after replenish.

In particular due to size limitations for the TLB often do not open all virtual pages using the TLB their corresponding physical pages are mapped. In addition, due to the strong oversize tion of the virtual address space compared to the physical Address space not all virtual pages on physical Pages are shown, it just has to be virtu there are all addresses for the physical addresses, where actually code or data for which is actually lukewarm tasks of a multitasking environment are saved. If a virtual page is not on a physical page is depicted that either does not exist or that no actual physical memory cell shows, a page fault is output, which indicates indicates that the virtual address was damaged or that an error occurred in the address translation.  

The present OF INVENTION 1 if no entry is found with a corresponding virtual address in the TLB, then, according dung the hardware state machine 18 a of FIG. Enabled to convert a virtual address which has not been found in the TLB to a physical address to load the physical address together with its virtual address into the TLB. For this purpose, as has been stated, the hardware state machine will access the non-volatile memory (e.g. 12 or 14 of FIG. 1) to determine the physical address using the mapping rule stored there.

According to the invention, a hierarchical tree is used as the illustration structure with physically addressed nodes preferred. A hierarchical tree structure that is also known as multilevel Page table mapping rule can be referred to has the advantage that not a large page table in the non- volatile memory must be kept, but that instead a large table has several levels or levels with smaller ones Lists can be used. This allows efficiency Management especially with small physical memory cherseiten.

The hardware state machine 18 a is then able to pass through the hierarchical tree structure from node to node in order to finally determine a physical address for a given virtual address. This process is called "page table walking".

Such a process is described with reference to FIG. 4a. In Fig. 4a shows a virtual address 400 is shown having various dene portions 402-310. Section 410 is assigned to a root level, ie the highest level. Section 408 is assigned to the next higher level, in the example level 4. Section 406 of virtual address 400 is assigned in accordance with level 3. Section 404 is assigned to level 2, while section 402 is assigned to level 1, ie the end node. The last section of the physical address, which can also be referred to as a section for level 0, contains the page offset, which is denoted in FIG. 3 by the reference symbol 38 . The virtual address also includes a so-called package address 412 , which addresses a memory package. In the preferred embodiment, the virtual address space is divided into 256 packages of the same size, so that each package has an address space of 16 MB. This makes it possible, for example, to assign different access rights for different storage packages in the virtual address space.

The section 410 of the virtual address 400 , which comprises only 1 bit in a preferred exemplary embodiment, is assigned to a root node of the hierarchical tree structure.

The list for the root node can be in the non-volatile or be stored in registers of the memory management unit. Alternatively, the list for the root node can also be on one fixed agreed abge in the physical memory lays down.

The list for the root node is referred to as package descriptor buffer 414 and, due to the fact that section 410 of virtual address 400 has only one bit, comprises only two list entries. An entry in the root list 414 includes an index indexed by the bit of section 410 of the virtual address. If the bit in section 410 has a value of one, as is the case in the example designated in FIG. 4a, the first entry in list 414 is selected. The entry further includes a pointer 416 to the physical address of the page in non-volatile memory, on which a list 418 is stored for the first intermediate node to which section 408 of virtual address 400 is associated. If, on the other hand, the bit in the section 410 of the virtual address is a zero, the second entry in the list 414 is selected, which comprises a pointer 420 to the physical address of a memory page in the non-volatile memory, in which a further list 422 for the first Intermediate node to which section 408 of virtual address 400 is assigned is stored. After the virtual address section 408 comprises four bits, the lists 418 and 422 for the first intermediate node each have 16 entries. Each entry has a length of. 32 bits, so that in the exemplary embodiment shown in FIG. 4a, each list takes up exactly one memory page in the non-volatile memory.

After the hardware state machine has determined the upper entry of the root list 414 based on the section 410 of the virtual address 400 , the hardware state machine can use the pointer 416 to access the physical memory page in which the list 418 for the first intermediate node is stored. The hardware state machine then reads in section 408 of virtual address 400 and, based on the fact that the section has the value "1100", selects the thirteenth entry in list 418 .

In addition to an entry index, the thirteenth entry includes a pointer 424 to a list 426 for a further intermediate node to which section 406 of virtual address 400 is assigned.

The hardware state machine then reads the section and selects the first entry from list 426 because section 406 has the value "0000".

The first entry in the list 426 in turn contains a pointer 428 to a list 430 which is assigned to a further intermediate node with a lower hierarchy. The hardware state machine now reads the section 404 of the virtual address 400 and selects the eighth entry of this list, since the value of the section 404 is "0111".

The selected entry of the list 430 in turn contains a pointer 432 to a physical address of the physical page in the non-volatile memory, in which a list 434 for an end node which is assigned to the section 402 of the virtual address 400 is stored. The hardware state machine now reads in section 402 of the virtual address and selects from list 434 the twentieth entry of list 434 based on the fact that the value of section 402 is "10011". Since the section 402 of the virtual address 400 is assigned to the end level, the selected entry of the list 434 for the end node contains a pointer 436 to the physical address of the physical side, which corresponds to the virtual start address of the virtual page. To the physical address to which the pointer 436 points, all that is now necessary is to add the page offset, as symbolically represented by a dashed arrow 438 in FIG. 4 a, in order to obtain the physical address 440 that of the virtual address 400 assigned.

It should be pointed out that the concept described in FIG. 4a can also be used if no page-by-page memory organization is used, but a direct addressing of memory cells without a page address and offset value. In this case, the last step, which is represented by arrow 438 in FIG. 4a, would simply be omitted.

As has already been stated, the virtual address space is considerably larger than the physical address space. For this case, there are many entries in the lists shown in FIG. 4 for the different nodes that do not refer to a next-lower node. In Fig. 4a, these are all entries that do not contain an exit pointer. These entries are also referred to as zero entries. Because of the clarity of the illustration, the lists assigned to the same have been omitted from all pointers which point into space in FIG. 4a. However, a complete mapping rule would include a corresponding list for each pointer in Figure 4a.

Apart from the PAD section 412 , in the exemplary embodiment shown in FIG. 4a, the virtual address 400 is divided into six parts or sections. Each section is assigned a level in the address translation process performed by the hardware state machine. The highest level, that is, level 5 , as it was done, indexes one of two entries in list 414 . Of course, list 414 could also contain several entries. In this case, the section 410 of the virtual address 40 would have to have more bits accordingly. With two bits, four entries could already exist in list 414 .

Fig. 4b shows the address range, which can be addressed to a certain extent by each level. The root list 414 (last row of the table in FIG. 4b) can address the entire 16 megabytes of the virtual address space, the upper pointer 416 selecting the upper eight megabytes, while the lower pointer 420 selects the lower eight megabytes , Therefore, the list 418 or, analogously, the list 422 can each address a physical address space of eight megabytes, with each entry in the list 418 , ie each arrow pointing out of the list 418 , being able to address 512 kilobytes. Each pointer from list 418 points to a list 426 of the third level (third line of the table in FIG. 4b). Similarly, each pointer from a third level list, such as. B. the pointer 428 , again address range of 32 kilobytes. The address range of 32 kilobytes is the address range that is spanned by the list 430 of the second level, where an address in this list in turn address an address range of two kilobytes can.

FIG. 5 shows a section of the hierarchical page table structure of FIG. 4a, but with a different virtual address, which in sections 408 and 406 has louder ones for the fourth level and for the third level. In contrast to the mapping rule shown in FIG. 4a, the mapping rule in the form of the hierarchical tree, which begins with the root list 414 and ends with the physical address 440 , allows a skipping of at least one level. The skipping of a level is signaled in the virtual address by a certain section, for example by the fact that there are loud ones in one section, as is the case in FIG. 5. However, any other predetermined code could also be reserved for skipping a level. The pointer, which starts from the root list 414 and is labeled 500 in FIG. 5, no longer points to a list of the fourth level or the third level, but immediately to the list 430 of the second level. It is possible to skip any number of levels or nodes. The bits in the virtual address that correspond to these levels must have the predetermined code to signal the level machine to skip levels. This optimization requires additional information for the pointer 500 , this additional information being stored in the entries in the root list 414 . Of course, only level 3 could be skipped, while the level 4 node must not be skipped. In this case, the additional information should be available in an entry in a list for the level 4 node.

In the following, reference is made to FIG. 6. Fig. 6 shows a table corresponding to Fig. 4a and Fig. 5 for the meaning of the bits of the virtual address and the relationship between the node size, ie the maximum number of entries in the node list. In other words, each row of the table in FIG. 6 represents a section of the level of the virtual address designated on the far left in FIG. 6. In the first row of the table of FIG. 6, which relates to level 5 , that is to say the root level, relates that the section 410 has only one bit, namely in the preferred embodiment of the present invention bit 23 of the virtual address. One bit can be used to index two different entries in the root list, so that the node size of the root node is 2 . The fourth level comprises bits 19-22 . Four bits can be used to index 16 different entries in a list for the fourth level, so that the node size, that is to say the size of a list in the fourth level, is 16 . The number of lists in the fourth level is 2 because the root list has two entries.

Both the section for the third level and the section for the second level both have four bits, so that a list of the second level or the third level can also have a maximum of 16 entries. The section 402 for the first level comprises five bits, so that through this section 32 entries of a list can be indexed, as is also clear from the list 434 for the first level of Fig. 4a, it has 32 lines while a list the second level has only 16 lines. The zero level, ie the page offset starting from a start page address, comprises six bits, so that 64 list entries can be indexed with it. After a physical page has 64 bytes, minimal offsets of one byte can be addressed. For example, if the page size were 128 bytes, the minimum memory size that can be addressed would be two bytes.

In the following, reference is made to FIG. 7. In FIG. 7, like in FIGS. 5 and 4a, entries used in a list are drawn in bold, while zero entries are shown as a blank rectangle. It is clear from the mapping rule shown in FIG. 7 that there are a large number of zero entries and only a few entries used. This is due to the fact that the virtual address space is considerably larger than the physical address space. In the preferred embodiment of the present invention, the virtual address space is 4 gigabytes, while the physical address space is only 4 megabytes. If a page-by-page storage organization is used, however, a storage page must nevertheless be provided for each list shown in FIG. 7. In the example of a mapping rule shown in FIG. 7, 10 memory pages must therefore be used in order to manage only 4 physical pages in which code or data are present. In applications where there is a sufficient amount of non-volatile memory to store the lists for the levels, this does not matter.

However, if the storage space is limited and a valuable one Is resource, so it is preferred to add the n-node lists compress to the ratio of the number of used Entries in a list of the total number of entries in the Enlarge list. It is therefore from the so-called n- Node passed to the q node. While the expression "n- Node "means that all lists of a node are one Level has the same number of entries, namely n entries, the expression "q-node" means that the node list is compressed is mated, and that the number of entries in a list for one and the same level can vary from list to list.

Partially filled node lists are compressed and, as is particularly explained with reference to FIG. 11, several compressed nodes can be stored on one side of the physical memory area. The compressed nodes are called q nodes, and the hierarchical tree structure with compressed nodes is referred to as the q tree.

The theory behind a q-knot is that all entries used in a list, d. H. all non- Null pointer, placed in an n-node in a structure can be (the q-node), which is smaller than the original che n node. This is accomplished by placing the n-node in smaller section is split, being for a maximum Compression the smallest section is taken of all Contains non-zero pointers. To position a pointer in to specify the n-node will be an offset value for the q node pointer required. This offset value is also called called virtual offset.

In the following, reference is made to FIG. 8 in order to illustrate a possible compression type of a list 800 of an n-node. List 800 includes two non-zero entries that can be binary indexed by 1100 and 1110. Possible q nodes are shown next to list 800 . In principle, three different "compressed" lists, ie q-nodes, 802 , 804 and 806, can be generated in the described compression. List 802 corresponds to list 800 . This is the trivial form of compression, the q-node list 802 is exactly the same size as the list 800 , and no offset bit is required. In contrast, list 804 is already compressed to half the storage space. The list contains two entries that can be indexed with 110 and 100. To get from the entries in the compressed list 804 to the entries in the uncompressed list 800 , a virtual offset bit is required, which has a value of 1. The virtual offset bit corresponds to the most significant bit (msb) of both entries in list 800 . Compression is therefore possible if the msbs of the non-zero entries in list 800 are the same. Since the most significant bits of the entries in the compressed list 804 are the same, even higher compression can be achieved, as the compressed list 806 shows. The two non-zero entries in list 806 have most significant bits that are not the same, so that no further compression is possible. In order to get from the compressed list 806 back to the uncompressed list 800 , two offset bits are required, namely the two most significant bits of the entries in the list 800 , which are the same for both non-zero entries in the list ,

Depending on the degree of compression of the node (no compression, a compression of 16 entries to 8 entries and finally a compression of 16 entries to 4 entries), the virtual offset value is 0, 1 bit or 2 bits. The compression to 8 entries, ie half a storage page, means that the pointers in the original n-node are only in either the upper or the lower half. The virtual offset must therefore be 1 bit to specify the position, the offset bit with a value of 0 means that all non-zero entries are in the lower half, while an offset bit of 1 means that all entries of the List in the top half of the n-node list 800 .

Analogously to this, as has been illustrated with reference to FIG. 8, a further compression is possible with the list 800 , since all non-zero entries are not only in the upper half but even in the upper quarter of the list. In this case, the offset bits are at a value of "11", indicating that the pointers can be found in the fourth quarter in the n-node list. If no compression is performed (list 802 ) because the compression method does not allow compression, as shown in FIG. 9, no offset bits are required. The size of the list in the next lower node is specified in the node list, which includes the pointer pointing to the next lower (compressed) node. For example, if list 430 of FIG. 4a is compressed, for example by half, entry 426 of the next higher list would specify the size of the list in addition to the physical address where list 430 is stored. The list 430 would then be, for example, a compression by half, only 8 entries large, although the section 404 of the virtual address which corresponds to level 2 has 4 bits and actually indexes a 16-entry list. Section 404 of the virtual address would then be designed such that one bit of it, typically the most significant bit, is interpreted as a virtual offset bit.

This also results in another control mechanism. The hardware state machine will compare the most significant bit of section 404 to the size bit in the non-zero entry of list 426 and continue address translation if matched, while if the bits do not match, a page fault is issued, since then at least either the mapping rule or the virtual address is incorrect.

In the following, FIG. 9 is discussed in order to show further examples of how n nodes can be reduced to their minimum q nodes if the compression method described with reference to FIG. 8 is used. The list 900 in Fig. 9 only includes a non-zero entry indexed by the bit combination "1100". The minimal q node comprises only a single entry and, accordingly, 4 virtual offset bits "1100". A list 900 with only a single non-zero entry can thus be reduced in a simple manner with respect to its memory space requirement by 1/16 times.

List 902 includes two non-zero entries that can be indexed with "0001" and "0011". The two entries have two equal most significant bits, so that two virtual offset bits 00 arise, and the list can be reduced by a quarter.

The list 904 comprises two non-zero entries, the most significant bits of which, however, are not the same, so that no compression can be achieved with the exemplary compression algorithm chosen here. The q-node is therefore exactly the same size as the n-node.

The sample list 906 includes two entries with "0100" and "0101". The three most significant bits are the same, so that 1/8 times compression can be achieved, resulting in the virtual offset bits "010".

The sample list 908 includes four non-zero entries between "1010" and "1101". All four entries have the same most significant bit, so that a compression ½ times he can be achieved, which leads to a virtual offset bit of "1".

It should be noted that the q-nodes of level 1 ( FIG. 4a) play a special role. Since their entries do not point to other q nodes, but directly to the physical memory pages, no additional information, such as. B. a size value of a hierarchically low q-list can be stored together with the pointers. As a result, an entry in a level 1 list is used to store two pointers. Therefore, the virtual address portion 402 associated with level 1 includes five virtual address bits. The additional bit specifies which of the pointers to use in the selected q-node entry. It should be noted that one of the two pointers can also be 0. After an entry in a level 1 list stores two pointers, the list length of a list, such as The list 434 of Fig. 4a, twice the length of a higher level list, such as. B. level 430 .

Reference is now made to Fig. 10 to illustrate how the compressed q nodes can be used to minimize memory usage. First, for example, according to the table in FIG. 9, the mini paint q nodes of a hierarchical mapping rule i are dentified. This results in a mapping rule as shown in FIG. 10. The filled rectangles indicate used entries, while the empty rectangles indicate zero entries. Each q-node is surrounded by a thick line. It can be seen that in the selected example of the mapping rule all lists except a list 1000 could be compressed. The list 1000 could not be compressed with the compression method chosen, since the two non-zero entries which comprise the same are not listed in the same half of the list.

In the mapping rule shown in FIG. 10, all, including the compressed, lists are each stored on their own physical memory pages or "page frames", so that the page frames are occupied very loosely, but the number of pages has not yet been reduced Frames reached. In the exemplary embodiment shown in FIG. 10, however, the unoccupied words in the page frames can already be occupied by other data, so that a list for the mapping rule and additional data can be stored in a physical memory page. For storage management reasons, however, it is preferred to proceed to a concept according to FIG. 11 in order to concentrate the mapping regulation information, that is to say the lists for the individual levels, in as few physical memory pages as possible, so that complete memory pages are freed up in order to be free of them to be able to save other data.

Since most q-nodes are small, in the mapping rule shown in FIG. 11, all node lists except a node list 1100 can be packed into the same physical memory page 1102 . As a result, the mapping rule or the page allocation structure is reduced from 10 to 2 memory pages. In this way, the q-tree structure provides considerable optimization compared to the option shown in Fig. 4a, in which no list compression has been performed.

The only "wasted" memory is due to the lists that contain multiple null pointers and cannot be further compressed. List 1100 falls into this category. Experience has shown, however, that there are few such q-nodes. Normal programs usually use at least some contiguous memory areas, such as. B. Code, static data, stack and heap. Storage layouts of this type have a smaller additional effort for the assignment structure. However, fragmented memory layouts are sometimes necessary.

Although only the list compression function shown in more detail in FIG. 9 has been shown above, it should be pointed out that all list compression methods can be used. The compression does not have to be based solely on the fact that entries must be in the same half or in the same quarter of a list. For example, list 1100 could be compressed by using an alternative compression method based on entries in different halves of the list. Depending on the layout of the virtual address and the meaning of the offset bits in a section of the virtual address, several different compression methods can also be combined if the storage requirements are such that even a small number of lists that are not compressed can, such as B. List 1100 of FIG. 11 is not acceptable.

In a preferred embodiment of the present invention, a node addressing mode (NAM) is provided in order to be able to modify the mapping rule in the non-volatile memory. The format for a virtual address 1200 shown in FIG. 12 is used for this. As in FIG. A, the virtual address is divided into several sections, the sections 1210 to 1202 in principle corresponding to the sections 410 to 402 of FIG. 4a. The last section 1212 , which had designated the offset value in FIG. 4a, is, however, used at the virtual address 1200 to signal the q-node level, the list of which is to be modified in NAM mode.

The NAM mode is used to manipulate virtual addresses, since for security reasons only a virtual addressing mode is to be used, so that the CPU has no direct access to physical pages. By setting the section 1212 of the virtual address 1200 , lists for individual levels and in particular the entries in these lists can be accessed.

For this purpose, each packet descriptor, which is stored in the root list 414 , ie the package descriptor buffer, comprises a NAM bit which, when set, allows access to the q-node lists for this special memory package. However, it should be noted that only packages in privileged layers, ie privileged modes of the operating system, can manipulate the NAM bit. When the NAM bit is set, the last portion 1212 of the virtual address is no longer interpreted as a page offset value, but is used to signal the hardware state machine whether the q-node is at level 4, level 3 Level 2 or level 1 should be addressed to access the list or entries in the corresponding list.

If the NAM bit is set, the virtual address is thus interpreted differently by the hardware state machine than in the case described in FIG. 4a.

The hardware state machine now, when the NAM bit is set, only performs address translation until the q-node of the stop level defined by section 1212 is recovered. Then a final bus cycle is generated on the physical side, which is indicated by the pointer of an entry in the list for the defined stop level. The requested list data is then accessed and is preferably stored in the data cache 20 ( FIG. 1). It should be noted that this address translation is not stored in TLB 18 b ( FIG. 1), since it is the mapping rule itself and not an assignment of a virtual address to a physical address.

LIST OF REFERENCE NUMBERS

10

CPU

12

ROME

14

NVM (E ²

PROM)

16

R.A.M.

18

Memory management unit

18

a hardware state machine

18

b Translation Look Aside Buffer (TLB)

20

Instruction / data cache

24

Data / Command Bus

26

Hardware state machine access bus

30

virtual memory page

32

mapping rule

33

Access mode bits

34

Task identifier bits

36

Address of a virtual page

38

Address offset of a virtual page

40

Access information

42

Virtual address column

44

Physical address column

46

page table

48

Access check module

50

Page Fault Module

52

physical address

400

virtual address

402

Section for level 1

404

Section for level 2

406

Section for level 3

408

Section for level 4

410

Section for level 5

412

packet address

414

Paketbeschreiberpuffer

416

Pointer to physical address

418

List for level 4

420

Pointer to physical address

422

List for level 4

424

Pointer to physical address

426

List for level 3

428

Pointer to physical address

430

List for level 2

432

Pointer to physical address

434

List for level 1

436

Pointer to physical address

438

Lateral offset value

440

physical address

500

Pointer to skip one or more levels

800

n-node list

802

uncompressed q-node list

804

simply compressed q-node list

806

doubly compressed q-node list

900

Example of n-node list

902

Example of n-node list

904

Example of n-node list

906

Example of n-node list

908

Example of n-node list

1000

uncompressed q-node list

1100

Memory page with a single uncompressed q-node list

1102

physical memory page with a plurality of compressed q-node lists

1200

virtual address for node addressing mode

1210

Section for level 5

1208

Section for level 4

1206

Section for level 3

1204

Section for level 2

1202

Section for level 1

1212

Section for identifying the list to be accessed

Claims (18)

1. Computer system with virtual addressing, a virtual address being assigned to a physical address via a mapping rule, with the following features:
a non-volatile memory ( 12 , 14 ) for storing at least a portion of the mapping specification; and
a hardware state machine ( 18 a) which can access the non-volatile memory ( 26 ) and is designed to use the virtual address and at least part of the mapping rule to determine the physical address assigned to the virtual address. 2. Computer system according to claim 1, wherein the virtual ad address one address for a virtual memory page and one virtual offset value includes a word in the virtual Address memory page, and where the physical Address an address for a physical memory page and includes a physical offset value to a word in the address physical memory page. 3. Computer system according to claim 2, in which the picture before font is designed such that the virtual memory page and the physical memory page are the same size, and the virtual offset value and the physical offset are the same size. 4. Computer system according to one of the preceding claims, the is arranged to initialize in a virtual mode become. 5. Computer system according to one of the preceding claims, further comprising the following features:
a volatile memory ( 18 b) in which assignments of physical addresses to virtual addresses can be stored,
wherein the computer system is arranged to first access the volatile memory ( 18 b) to determine whether a requested virtual address is stored, and
wherein the computer system is arranged to activate the hardware state machine ( 18 a) for an address translation if the requested virtual address is not stored in the volatile memory ( 18 b). 6. Computer system according to one of the preceding claims,
in which the mapping rule is structured hierarchically as a tree with nodes ( 414 , 418 , 422 , 426 , 430 , 434 ), the tree being a root node ( 414 ), at least one intermediate node ( 418 , 422 , 426 , 430 ) and an end node ( 434 ) has,
in which a list for a node is stored in the non-volatile memory, the list of a node having entries, an entry having an entry index and a pointer ( 424 , 428 , 432 , 436 ) to a physical address, where the pointer for the physical address points to a physical address of the non-volatile memory, with which a list can be retrieved for another node of the tree,
in which the virtual address ( 400 ) is divided into sections ( 402 , 404 , 406 , 408 , 410 ), whereby for the root node ( 414 ), the at least one intermediate node ( 418 , 422 , 426 , 430 ) and the end node ( 434 ) a section is present, the section ( 402 , 404 , 406 , 408 , 410 ) identifying a list entry of an associated list, and
in which the hardware state machine ( 18 a) is arranged to extract a section from the virtual address in order to access the non-volatile memory ( 12 , 14 ) in order to use the extracted section to make an entry in a list for the node associated with the section and to continue extracting and accessing sequentially until the end node is reached to obtain the physical address ( 440 ) associated with the virtual address ( 400 ). 7. Computer system according to claim 6,
in which the packet description buffer ( 414 ) has a non-volatile memory portion in which the list for a root node of the mapping rule is stored,
wherein the list ( 414 ) for the root node has at least two entries, each entry having the physical address ( 416 ) of a list for an intermediate node of a lower node level, and
wherein the virtual address has a root section ( 410 ) that identifies the entry in the root list for the virtual address. 8. Computer system according to claim 6 or 7,
in which the hardware state machine ( 18 a) is designed to skip an intermediate node level ( 500 ) when the portion ( 406 , 408 ) of the virtual address ( 400 ) that is assigned to the intermediate node level has a predetermined value has, and
in which, in the event of an intermediate node skipping, the entry in a list of the output node has the physical address of a list of a jump output node that follows a skipped node in the hierarchical tree. 9. Computer system according to one of claims 6 to 8,
where the number of virtual addresses is greater than the number of physical addresses, so that a list has empty entries that do not refer to a physical address,
wherein the node's list stored in the non-volatile memory is compressed so that the ratio of the number of entries containing a pointer to a physical address to the total number of entries in the list compared to an uncompressed list is increased, and
where an entry in the list identifies the compression of the node to which the list belongs or the compression of a lower node in the hierarchy. 10. Computer system according to claim 9, in which the non-volatile memory ( 12 , 14 ) is organized page by page,
in which at least two compressed lists are stored in the same memory page ( 1102 ), and
in which a list entry of a list of a higher node comprises the physical address of the memory page and a value at which the list of the lower node is stored in the memory page. 11. Computer system according to claim 10, in which in a storage page of the non-volatile memory ( 12 , 14 ) only compressed lists are stored, the number of entries of which are the same size after compression. 12. Computer system according to one of claims 6 to 11,
in which the lists traversed for a virtual address have access rights information (EAR) for the virtual address which identify whether or how, in an operating mode of the computer system, to data at the physical address which is assigned to the virtual address by the imaging rule, can be accessed, and
in which the TLB ( 18 b) is arranged to carry out an access rights check ( 48 ) on the basis of the access rights information before a physical address is determined. 13. Computer system according to one of claims 6 to 12,
in which the hardware state machine ( 18 a) is arranged to be placed in a node addressing mode, and
in which the virtual address is designed to identify, via a section ( 1212 ) thereof, the node whose list is to be accessed. 14. Computer system according to one of the preceding claims, that is intended for safety-relevant applications. 15. Computer system according to one of the preceding claims, which is integrated on a chip card. 16. Computer system according to one of the preceding claims, where at least the part of the in the non-volatile memory stored image specification in the form of a ROM Mask programmed in the manufacture of the computer system becomes. 17. A method for determining a physical address from a virtual address, comprising the following steps:
Obtaining a virtual address;
Access ( 26 ) to a non-volatile memory ( 12 , 14 ) in which at least part of a mapping rule is stored, via which the virtual address is uniquely assigned to a physical address;
Determining ( 18 a) the physical address using at least the part of the mapping rule stored in the non-volatile memory; and
Output of the determined physical address. 18. The method according to claim 17, wherein the mapping rule is hierarchically structured as a tree with nodes ( 414 , 418 , 422 , 426 , 430 , 434 ), the tree being a root node ( 414 ), at least one intermediate node ( 418 , 422 , 426 , 430 ) and an end node ( 434 ),
in which a list for a node is stored in the non-volatile memory, the list of a node having entries, an entry having an entry index and a pointer ( 424 , 428 , 432 , 436 ) to a physical address, where the pointer for the physical address points to a physical address of the non-volatile memory, with which a list can be retrieved for another node of the tree,
in which the virtual address ( 400 ) is divided into sections ( 402 , 404 , 406 , 408 , 410 ), whereby for the root node ( 414 ), the at least one intermediate node ( 418 , 422 , 426 , 430 ) and the end node ( 434 ) a section is present, the section ( 402 , 404 , 406 , 408 , 410 ) identifying a list entry of an associated list, and
in which the step of determining comprises the following steps:
Extracting a section ( 410 ) for the root node from the virtual address ( 400 );
Accessing a list ( 414 ) associated with the extracted portion ( 410 ) of the virtual address to obtain a pointer ( 416 ) to a physical address of a list for an intermediate node;
Extracting a section ( 408 ) from the virtual address ( 400 ) for the intermediate node;
Accessing an entry in the list using the extracted section ( 408 ) to retrieve a pointer ( 424 ) to a physical address where a list ( 426 ) for a lower section is stored; and
Repeating the extracting and accessing steps until all portions of the virtual address are processed to determine the physical address ( 440 ) that the virtu. Using the list for the end node and a portion ( 402 ) of the virtual address for the end node assigned address ( 400 ).