Memory access protection apparatus and methods for memory mapped access between independently operable processors

• US 10,191,859 B2
• Filed: 09/20/2016
• Issued: 01/29/2019
• Est. Priority Date: 03/31/2016
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Garg, Saurabh, Sanghi, Karan, Petkov, Vladislav, Zhang, Haining
• Primary Examiner(s): Thai, Tuan
• Assistant Examiner(s): Matin, Tasnima
• Application Number:
  US15/271,109
• Publication Number:
  US 20170286323A1
• Time in Patent Office: 861 Days
• CPC Class Codes: G06F 12/1081 for peripheral access to main memory, e.g. direct memory access [DMA]
• CPC Class Codes: G06F 12/1441 for a range
• CPC Class Codes: G06F 2212/1052 Security improvement

Abstract

Methods and apparatus for providing access to a shared memory resource. In one embodiment, a first processor generates a first window register associated with the shared memory resource; and transmits the first window register from the first processor to a second processor, the first window register defining a first extent of address space within the shared memory resource that is directly accessible by the second processor without requiring a performance of arbitration operations by the first processor.

Claims

1. A method for providing access to a shared memory resource, comprising:

during a boot process of a second processor;

generating, by a first processor, a first window register value associated with the shared memory resource;

transmitting the first window register value from the first processor to a window register of the second processor, the first window register value defining a first extent of address space within the shared memory resource that is directly accessible by the second processor; and

wherein the first extent of address space is mapped to a memory map of the second processor during the boot process.

2. The method of claim 1, wherein the generation of the first window register value comprises:

generating, by the first processor, a base address that corresponds to a starting location within the shared memory resource; and

generating, by the first processor, a window length that corresponds to the first extent of address space within the shared memory resource from the starting location within the shared memory resource.

3. The method of claim 1, further comprising:

generating, by the first processor, a second window register value associated with the shared memory resource; and

transmitting the second window register value from the first processor to the second processor, the second window register value defining a second extent of address space within the shared memory resource that is directly accessible by the second processor.

4. The method of claim 1, further comprising:

responsive to an attempt to access an extent of address space outside of the first extent of address space, receiving a nullified packet transmitted by the second processor.

5. The method of claim 4, wherein the reception of the nullified packet by the first processor, further comprises receiving an inverted data link layer cyclic redundancy check (LCRC) value for the nullified packet.

6. The method of claim 4, wherein upon reception of the nullified packet by the first processor, disregarding the nullified packet.

7. A computing device comprising a memory mapped system, the computing device comprising:

a host processing device comprising a host central processing unit (CPU) and a host memory management unit (MMU);

a peripheral processing device comprising a peripheral CPU, a peripheral MMU, peripheral memory and a peripheral direct memory access (DMA) unit; and

a host memory accessible by both the host processing device and the peripheral processing device;

wherein the host processing device further comprises logic configured to;

generate a first window register value associated with the host memory;

transmit the first window register value from the host processing device to the peripheral processing device, the first window register value defining a first extent of address space within the host memory that is directly accessible by the peripheral processing device and that prevents write access of the first extent of address space within the host memory by the host processing device.

8. The computing device of claim 7, wherein the first window register value is defined by the host processing device during a boot process for the peripheral processing device.

9. The computing device of claim 7, wherein the first window register value comprises both:

(1) a base address, and (2) a window length, the base address and the window length configured to define the first extent of address space within the host memory.

10. The computing device of claim 7, wherein the memory mapped system further comprises a window configuration register, the window configuration register configured to be read and/or written by the host processing device and the peripheral processing device.

11. The computing device of claim 10, wherein the window configuration register further comprises an available window field and the peripheral processing device is further configured to write a value into the available window field;

and

wherein the host processing device is further configured to read the value in the available window field, the read value being utilized by the host processing device in order to determine whether the host processing device should write a value to a windows enabled field of the window configuration register.

12. The computing device of claim 11, wherein the host processing device is further configured to write a default value to the windows enabled field of the window configuration register, the default value being indicative of a legacy peripheral processing device that is incompatible with support of one or more window registers.

13. The computing device of claim 10, wherein the host processing device is further configured to write to one or more locking bits of the window configuration register, the one or more locking bits configured to prevent an update of any fields located within one or more window registers.

14. A peripheral processing device configured to access host memory within a memory mapped system, the peripheral processing device comprising:

a peripheral central processing unit (CPU), a peripheral memory management unit (MMU), a peripheral memory and a peripheral direct memory access (DMA) unit and further comprising logic configured to;

receive a first window register value from a host processing device during a boot process of the peripheral processing device, the first window register value defining a first extent of address space within the host memory resource that is directly accessible by the peripheral processing device and is not write accessible by the host processing device.

15. The peripheral processing device of claim 14, further comprising logic configured to:

expose a capability register which the host processing device can access, the capability register comprising a windows enabled field and a windows available field.

16. The peripheral processing device of claim 15, further comprising logic configured to:

write a first value into the windows available field, the first value comprising a maximum number of windows supported by the peripheral processing device.

17. The peripheral processing device of claim 16, further comprising logic configured to:

read a second value from the windows enabled field, the second value indicating to the peripheral processing device a number of windows enabled by the host processing device.