Abstract: An apparatus and method are provided for handling prediction information. The apparatus has processing circuitry for performing data processing operations in response to instructions, the processing circuitry comprising transactional memory support circuitry to support execution of a transaction comprising a sequence of instructions. Prediction circuitry is used to generate predictions in relation to instruction flow changing instructions, and prediction storage is provided to store a plurality of items of prediction information that are referenced by the prediction circuitry when generating the predictions. The items of prediction information maintained by the prediction storage change based on the instructions being executed by the processing circuitry. A recovery storage is activated by the transactional memory support circuitry at a transaction start point to store a restore pointer identifying a chosen location in the prediction storage.

Abstract: A tag check performed for a memory access operation comprises determining whether an address tag associated with a target address of the access corresponds to a guard tag stored in the memory system associated with a memory system location to be accessed. A given tag check architecturally required for a tag-checked load operation can be skipped when a number of tag-check-skip conditions are satisfied, including at least: that there is an older tag-checked store operation awaiting a pending tag check, for which a guard tag checked in the pending tag check is associated with a same block of one or more memory system locations as a guard tag to be checked in the given tag check; and that the address tag for the tag-checked load operation is the same as the address tag for the older tag-checked store operation.

Abstract: Data processing apparatus comprises a processing element configured to access an architectural register representing a given system register; mapping circuitry to map the architectural register representing the given system register to a physical register selected from a set of physical registers; a register bank having a set of two or more respective banked versions of the given system register, in which a respective one of the banked versions of the system register is associated with each of a plurality of current operating states of the processing element; in which, when the processing element changes operating state from a first operating state associated with a first one of the banked versions of the system register to a second operating state associated with a second, different, one of the banked versions of the system register, the processing element is configured to store the current contents of the architectural register representing the given system register to the first one of the banked versions o

Abstract: An apparatus and method are provided for processing instructions. The apparatus has execution circuitry for executing instructions, where each instruction requires an associated operation to be performed using one or more source operand values in order to produce a result value. Issue circuitry is used to maintain a record of pending instructions awaiting execution by the execution circuitry, and prediction circuitry is used to produce a predicted source operand value for a chosen pending instruction. Optimisation circuitry is then arranged to detect an optimisation condition for the chosen pending instruction when the predicted source operand value is such that, having regard to the associated operation for the chosen pending instruction, the result value is known without performing the associated operation.

Abstract: An apparatus comprises execution circuitry to perform operations on source data values and to generate result data values; issue circuitry comprising one or more issue queues identifying pending operations awaiting performance by the execution circuitry, and selection circuitry to select pending operations to issue to the execution circuitry; data value cache storage comprising first and second cache regions; and cache control circuitry to control the storing to the first cache region of result data values generated by the execution circuitry and the eviction of stored result data values from the first cache region in response to newly generated result data values being stored in the first cache region; the cache control circuitry being configured to store to the second cache region result data values required as source data values for one or more oldest pending operations identified by the one or more issue queues and to inhibit eviction of a given result data value stored in the second cache region until in

Abstract: A data processing apparatus comprises branch prediction circuitry adapted to store at least one branch prediction state entry in relation to a stream of instructions, input circuitry to receive at least one input to generate a new branch prediction state entry, wherein the at least one input comprises a plurality of bits; and coding circuitry adapted to perform an encoding operation to encode at least some of the plurality of bits based on a value associated with a current execution environment in which the stream of instructions is being executed. This guards against potential attacks which exploit the ability for branch prediction entries trained by one execution environment to be used by another execution environment as a basis for branch predictions.

Abstract: An apparatus comprising processing circuitry is provided, the processing circuitry comprising execution circuitry, commit circuitry, issue circuitry comprising an issue queue and selection circuitry, and a branch predictor. The processing circuitry is configured to identify a speculation barrier instruction in the commit queue. While an entry in the commit queue identifies a speculation barrier instruction, when a branch instruction that follows the speculation barrier instruction in the program order is selected for issue, the processing circuitry performs a first execution of the instruction, inhibiting updating of branch prediction data items associated with the branch instruction and inhibiting the selection circuitry from invalidating the associated issue queue entry.

Abstract: Coherency control circuitry (10) supports processing of a safe-speculative-read transaction received from a requesting master device (4). The safe-speculative-read transaction is of a type requesting that target data is returned to a requesting cache (11) of the requesting master device (4) while prohibiting any change in coherency state associated with the target data in other caches (12) in response to the safe-speculative-read transaction. In response, at least when the target data is cached in a second cache associated with a second master device, at least one of the coherency control circuitry (10) and the second cache (12) is configured to return a safe-speculative-read response while maintaining the target data in the same coherency state within the second cache. This helps to mitigate against speculative side-channel attacks.

Abstract: An apparatus and method are provided for controlling allocation of instructions into an instruction cache storage. The apparatus comprises processing circuitry to execute instructions, fetch circuitry to fetch instructions from memory for execution by the processing circuitry, and an instruction cache storage to store instructions fetched from the memory by the fetch circuitry. Cache control circuitry is responsive to the fetch circuitry fetching a target instruction from a memory address determined as a target address of an instruction flow changing instruction, at least when the memory address is within a specific address range, to prevent allocation of the fetched target instruction into the instruction cache storage unless the fetched target instruction is at least one specific type of instruction. It has been found that such an approach can inhibit the performance of speculation-based caching timing side-channel attacks.

Abstract: An apparatus and method of operating a data processing apparatus are disclosed. The apparatus comprises data processing circuitry to perform data processing operations in response to a sequence of instructions, wherein the data processing circuitry is capable of performing speculative execution of at least some of the sequence of instructions. A cache structure comprising entries stores temporary copies of data items which are subjected to the data processing operations and speculative execution tracking circuitry monitors correctness of the speculative execution and responsive to indication of incorrect speculative execution to cause entries in the cache structure allocated by the incorrect speculative execution to be evicted from the cache structure.

Abstract: Examples of the present disclosure relate to an apparatus comprising execution circuitry to execute instructions defining data processing operations on data items. The apparatus comprises cache storage to store temporary copies of the data items. The apparatus comprises prefetching circuitry to a) predict that a data item will be subject to the data processing operations by the execution circuitry by determining that the data item is consistent with an extrapolation of previous data item retrieval by the execution circuitry, and identifying that at least one control flow element of the instructions indicates that the data item will be subject to the data processing operations by the execution circuitry; and b) prefetch the data item into the cache storage.

Abstract: An apparatus (2) has processing circuitry to process micro-operations, the processing circuitry supporting speculative processing of read micro-operations for reading data from a memory system. A cache (6, 8) is provided to cache the micro-operations or instructions decoded to generate the micro-operations. Profiling circuitry (40) annotates at least one cached micro-operation or instruction with annotation information depending on analysis of whether a read micro-operation satisfies a speculative side-channel condition indicative of a risk of information leakage if the read micro-operation is processed speculatively. The processing circuitry (12, 14) determines whether to trigger a speculative side-channel mitigation measure depending on the annotation information stored in the cache (6, 8).

Abstract: An apparatus comprises processing circuitry 14 to perform data processing in response to instructions, the processing circuitry supporting speculative processing of read operations for reading data from a memory system 20, 22; and control circuitry 12, 14, 20 to identify whether a sequence of instructions to be processed by the processing circuitry includes a speculative side-channel hint instruction indicative of whether there is a risk of information leakage if at least one subsequent read operation is processed speculatively, and to determine whether to trigger a speculative side-channel mitigation measure depending on whether the instructions include the speculative side-channel hint instruction. This can help to reduce the performance impact of measures taken to protect against speculative side-channel attacks.

Abstract: An apparatus and method are provided for performing branch prediction. The apparatus has processing circuitry for executing instructions, and branch prediction circuitry for making branch outcome predictions in respect of branch instructions. The branch prediction circuitry includes loop prediction circuitry having a plurality of entries, where each entry is used to maintain branch outcome prediction information for a loop controlling branch instruction that controls repeated execution of a loop comprising a number of instructions. The branch prediction circuitry is arranged to analyse blocks of instructions and to produce a prediction result for each block that is dependent on branch outcome predictions made for any branch instructions appearing in the associated block. A prediction queue then stores the prediction results produced by the branch prediction circuitry in order to determine the instructions to be executed by the processing circuitry.

Abstract: An apparatus and method are provided for handling prediction information. The apparatus has processing circuitry for performing data processing operations in response to instructions, the processing circuitry comprising transactional memory support circuitry to support execution of a transaction comprising a sequence of instructions. Prediction circuitry is used to generate predictions in relation to instruction flow changing instructions, and prediction storage is provided to store a plurality of items of prediction information that are referenced by the prediction circuitry when generating the predictions. The items of prediction information maintained by the prediction storage change based on the instructions being executed by the processing circuitry. A recovery storage is activated by the transactional memory support circuitry at a transaction start point to store a restore pointer identifying a chosen location in the prediction storage.

Abstract: An apparatus and method of operating an apparatus are disclosed. The apparatus has a program counter permitted range storage element defining a permitted range of program counter values for the sequence of instructions it executes. Branch prediction circuitry predicts target instruction addresses for branch instructions. In response to a program counter modifying event, a program counter speculative range storage element is updated corresponding to each speculatively executed instruction after a branch instruction. Program counter permitted range verification circuitry is responsive to resolution of a modification of the program counter permitted range indication resulting from the program counter modifying event to determine whether the speculatively executed program counter range satisfies the permitted range of program counter values. A branch mis-prediction mechanism may support the response of the apparatus if the permitted range of program counter values is violated.

Abstract: An apparatus comprises execution circuitry to perform operations on source data values and to generate result data values; issue circuitry comprising one or more issue queues identifying pending operations awaiting performance by the execution circuitry, and selection circuitry to select pending operations to issue to the execution circuitry; data value cache storage comprising first and second cache regions; and cache control circuitry to control the storing to the first cache region of result data values generated by the execution circuitry and the eviction of stored result data values from the first cache region in response to newly generated result data values being stored in the first cache region; the cache control circuitry being configured to store to the second cache region result data values required as source data values for one or more oldest pending operations identified by the one or more issue queues and to inhibit eviction of a given result data value stored in the second cache region until in

Abstract: An apparatus comprising processing circuitry is provided, the processing circuitry comprising execution circuitry, commit circuitry, issue circuitry comprising an issue queue and selection circuitry, and a branch predictor. The processing circuitry is configured to identify a speculation barrier instruction in the commit queue. While an entry in the commit queue identifies a speculation barrier instruction, when a branch instruction that follows the speculation barrier instruction in the program order is selected for issue, the processing circuitry performs a first execution of the instruction, inhibiting updating of branch prediction data items associated with the branch instruction and inhibiting the selection circuitry from invalidating the associated issue queue entry.

Abstract: Data processing apparatus comprises a processing element configured to access an architectural register representing a given system register; mapping circuitry to map the architectural register representing the given system register to a physical register selected from a set of physical registers; a register bank having a set of two or more respective banked versions of the given system register, in which a respective one of the banked versions of the system register is associated with each of a plurality of current operating states of the processing element; in which, when the processing element changes operating state from a first operating state associated with a first one of the banked versions of the system register to a second operating state associated with a second, different, one of the banked versions of the system register, the processing element is configured to store the current contents of the architectural register representing the given system register to the first one of the banked versions o

Abstract: An apparatus and method are provided for performing branch prediction. The apparatus has processing circuitry for executing instructions, and branch prediction circuitry for making branch outcome predictions in respect of branch instructions. The branch prediction circuitry includes loop prediction circuitry having a plurality of entries, where each entry is used to maintain branch outcome prediction information for a loop controlling branch instruction that controls repeated execution of a loop comprising a number of instructions. The branch prediction circuitry is arranged to analyse blocks of instructions and to produce a prediction result for each block that is dependent on branch outcome predictions made for any branch instructions appearing in the associated block. A prediction queue then stores the prediction results produced by the branch prediction circuitry in order to determine the instructions to be executed by the processing circuitry.