An apparatus and method for controlling allocation of data into a cache storage

Abstract

An apparatus and method are provided for controlling allocation of data into cache storage. The apparatus comprises processing circuitry for executing instructions, and a cache storage for storing data accessed when executing the instructions. Cache control circuitry is arranged, whilst a sensitive allocation condition is determined to exist, to be responsive to the processing circuitry speculatively executing a memory access instruction that identifies data to be allocated into the cache storage, to allocate the data into the cache storage and to set a conditional allocation flag in association with the data allocated into the cache storage. The cache control circuitry is then responsive to detecting an allocation resolution event, to determine based on the type of the allocation resolution event whether to clear the conditional allocation flag such that the data is thereafter treated as unconditionally allocated, or to cause invalidation of the data in the cache storage. Such an approach can reduce the vulnerability of a cache to speculation-based cache timing side-channel attacks.

Description

technical field [0001] This disclosure relates to techniques for controlling the allocation of data into cache storage. Background technique [0002] The data processing apparatus may support speculative execution of instructions, wherein instructions are executed before it is known whether the instruction's input operands are correct or whether the instruction needs to be executed at all. For example, a processing device may have a branch predictor for predicting the outcome of a branch instruction so that subsequent instructions may be speculatively fetched, decoded, and executed before knowing what the actual outcome of the branch should be. In addition, some systems may also support speculative data prefetching as a form, in which values ​​are loaded from memory in anticipation of the values ​​being needed by processing circuitry to allow subsequent instructions to be processed more quickly. Other forms of speculation are also possible. [0003] It has recently been id...

AI Technical Summary

Problems solved by technology

For example, information has recently been published on speculative-based cache timing side-channel attacks, where several techniques can be used such that cache timing analysis can be abused to leak information from misspeculative execution of instructions

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