Speculative execution in computer architecture

However, traditional mechanisms to support exceptions and speculative execution are highly intrusive to gpu hardware design. Speculative execution an overview sciencedirect topics. Speculative execution in a distributed file system edmund b. A second access request from a second component may be detected with respect to the set of memory spaces of the single shared. Provide many instructions provide many addressing modes. Intel analysis of speculative execution side channels download pdf white paper. If the tasks are required, a speedup is achieved, because the work is already complete. Speculative execution, the base on which modern highperformance generalpurpose cpus are built on, has recently been shown to en able a slew of security attacks. Predication and speculation department of computer. The cpu may execute certain tasks ahead of time, speculating that they will be needed. Fall 2019 cs3853 computer architecture speculative execution and security 34 speculative execution is an optimization technique where a computer system performs some task that may not be needed or should not be executed. Exploiting speculative execution paul kocher1, jann horn2, anders fogh3, daniel genkin4, daniel gruss5, werner haas6, mike hamburg7, moritz lipp5, stefan mangard5, thomas prescher6, michael schwarz5, yuval yarom8 1 independent. Speculative execution is an optimization technique where a computer system performs some task that may not be needed.

And speculative execution, while implemented differently from company to company, is. Work is done before it is known whether it is actually needed, so as to prevent a delay that would have to be incurred by doing the work after it is known that it is needed. In power and performance in enterprise systems, 2015. Zilles and sohi, execution based prediction using speculative slices, isca 2001. It allows multiple processes to share speculative state. During speculative execution, the architectural state of the system is kept unmodified, until the speculation can be. Background long tradition of research on speculation for computer architecture. How much slower would processors be without speculative. A technique allows a superscalar processor to keep its functional units as busy as possible by executing instructions before it is known that they will be needed. Processors without speculative execution will be much slower. Since the speculative task and the original task both are working on the same set of data, output of which ever task finishes first successfully is used and the other one is killed. Every single highend cpu architecture today amd, arm, ibm, intel, sparc uses outoforder execution. There is no reference book that focus on the most dynamic subject of speculative execution that holds the key to the future high performance computer architectures.

Spring 2020 cs3853 computer architecture speculative execution and security 39 speculative execution is an optimization technique where a computer system performs some task that may not be needed or should not be executed. Speculative execution can be exploited by priming the branch predictor with sufficient history such that it is tricked into predicting the wrong target for a branch. To me, outoforder execution is a form of speculative execution speculating that the inflight insts wont have side effects relevant to the new insts. Before commitment of the program portions in a sequential execution order, data dependencies are resolved through a token system that.

Hill, jouppi, sohi, dataflow and multithreading, pp. Speculative execution in highperformance computer architectures. Exception support and speculative execution are the next steps to expand the scope and improve the usability of gpus. By exploiting the speculative execution of modern processors, spectre attack can trick the system into executing instructions that are not supposed to be executed given the current system state 22. All that is technically meant by the term is that the execution of machine instructions on a computer is not actually intended to be all that secure or reliable. Architectural support for lockfree data structures, isca 1993. The computer architecture group at ucsd is at the cutting edge of innovation in computer architecture and systems design. Intel analysis of speculative execution side channels. Speculative execution in hadoop mapreduce is an optimization where slow running map or reduce tasks are started on another node too. Almost none of the major computer architecture conferences in recent years can go without including some papers touched on the subject of speculative execution. New speculativeexecution vulnerability strikes amd, arm. Speculative execution is extensive in modern processors. Our current projects address the current grand challenge of computer architecture.

The art and science of introducing new side channel vulnerabilities. This article will be updated as additional information becomes available. New speculativeexecution vulnerability strikes amd, arm, and intel fortunately, existing fixes should provide the protection we need. Speculative architecture is a collaborative studio practice, led by dirk yates, that specialises in the design and delivery of public and educational buildings. A first access request from a first component may be detected with respect to a set of memory spaces of a single shared memory in the coherent accelerator architecture. Speculative execution in modern computer architectures. Pdf efficient invisible speculative execution through. This exploit, coupled with a sidechannel attack, can lead to the exposure and theft of critical secret information. Provides an analysis of speculative execution security risks based on sidechannel analysis methods documented by. Speculative execution arvind computer science and artificial intelligence laboratory m.

Note that speculative execution can be applied even if there isnt an actual conditional branch in the code. Ece 4750 computer architecture, fall 2019 t14 advanced. Speculative execution in high performance computer. Speculation also known as speculative loading, is a process implemented in explicitly parallel instruction computing epic processors and their compiler s to reduce processormemory exchanging bottlenecks or latency by putting all the data into memory in advance of an actual load instruction. Speculative execution with late recovery every instruction is actually speculative because an older in. If the branch prediction was correct, the result is used, otherwise it is discarded. Enabling highly concurrent multithreaded execution, micro 2001. Technically, ooo is the ability to move execution between different dependency chains, so skipping an inst and moving to the next one. Us10169108b2 speculative execution management in a.

Brief history of computer architecture predication and speculation compiling for ia64 b a s1 c move code above a split cs553 lecture predication and speculation 3 a brief history of computer architecture the early years. Building a highly scalable singlethread instruction window, pact 2005. Finding powerefficient ways to find and exploit parallelism to continue scaling performance. The first book to describe some of the speculative execution techniques used to overcome performance problems in modern computer architectures, this book discusses research projects and commercial. Speculative execution in high performance computer architectures describes many recent advances in speculative execution techniques. Disclosed aspects relate to speculative execution management in a coherent accelerator architecture. Predictive execution is a form of speculative execution where some outcome is predicted and execution proceeds along the predicted path until the actual result is known. We have developed projects with institutional organisations including the queensland government, brisbane city council, museum of brisbane, and institute of modern art. Speculative execution involves executing instructions that we are not 100% sure will be executed. Chen, and jason flinn department of electrical engineering and computer science university of michigan abstract speculator provides linux kernel support for speculative execution. Speculative execution goes one step further and determines what the result would be from executing the next instructions.

Speculative execution, the base on which modern highperformance generalpurpose cpus are built on, has recently been shown to enable a slew of security attacks. Us10209997b2 computer architecture for speculative. Please check back here regularly for updates and new faq. Speculative execution wikimili, the free encyclopedia. Microsoft is aware of a new publicly disclosed class of vulnerabilities that are called speculative execution sidechannel attacks and that affect many modern processors including intel, amd, via, and arm. When combined with good branch prediction, speculative execution increases performance. Speculative execution is not really about computer machine architecture at all. Until now, there were few textbooks that focused on the dynamic subject of speculative execution, a topic that is crucial to the development of high performance computer architectures.

A system for parallel execution of program portions on different processors permits speculative execution of the program portions before a determination is made as to whether there is a data dependency between the portion and older but unexecuted portions. It covers cuttingedge research projects, as well as numerous commercial implementations that demonstrate the value of this latencyhiding technique. Speculative execution can provide a significant increase in performance, but has been shown to endanger the security of. Smith, a pipelined, shared resource mimd computer, icpp 1978. Readings required hill, jouppi, sohi, multiprocessors and multicomputers, pp. Speculative execution in high performance computer architectures describes many recent advances in speculative exec. Hence, in this paper we describe the application of multipath execution in a system developed to execute sequential programs using parallel and speculative techniques for the computer cluster architecture that. In general, the optimizations discussed in this chapter focus on avoiding the overhead associated with a branch. While speculative execution never hurts performance, it can be poorly utilized by software, leading to a high performance opportunity cost, that is, the performance that could have been achieved had the code been tuned better.