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Filtering coherency protocol transactions

  • US 10,664,399 B2
  • Filed: 11/29/2017
  • Issued: 05/26/2020
  • Est. Priority Date: 12/02/2016
  • Status: Active Grant
First Claim
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1. An apparatus comprising:

  • a filter comprising;

    interface circuitry to intercept coherency protocol transactions exchanged between a first master device and an interconnect for managing coherency between a first cache comprised by said first master device and at least one other cache or a second master device; and

    filtering circuitry to filter the coherency protocol transactions in dependence on memory access permission data defining which regions of an address space the first master device is allowed to access;

    wherein in response to an outgoing coherency protocol transaction issued from said first master device to said interconnect after a lookup in the first cache by the first master device, the filtering circuitry is configured to block the outgoing coherency protocol transaction when a memory access permission violation is detected for the outgoing coherency protocol transaction in dependence on the memory access permission data; and

    wherein the filtering circuitry is configured to detect said memory access permission violation when the outgoing coherency protocol transaction is a read transaction capable of causing data to be stored in said first cache in a shareable modifiable coherency state in which coherency is to be maintained between the data in said first cache and said at least one other cache or the second master device, and the first master device is allowed to modify the data without issuing a further coherency protocol transaction to said interconnect, and the memory access permission data specifies that the first master device is;

    prohibited from writing data to a region of the address space including a target address specified by the outgoing coherency protocol transaction; and

    permitted to read data from said region of the address space including the target address specified by the outgoing coherency protocol transaction.

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