Speculative execution an overview sciencedirect topics. A meltdown in computer architecture, as spectre haunts. Speculative execution in high performance computer. If youre looking for a free download links of inside the machine. In a race to make things faster and better and stronger, weve once again stumbled into danger, or flown too close to the sun. This text will also serve as a useful resource for all computer professionals and engineers who need an overview or introduction to computer architecture. Speculative execution is an optimization technique where a computer system performs some. Speculative execution in high performance computer architectures describes many recent advances in speculative exec. It is developed to use the benefit of prefetching capability of the hidisc on the current multithreaded processors such as simultaneous multithreading or chip multiprocessor. Decoupled memory access architectures with speculative pre. All that is technically meant by the term is that the execution of machine instructions on a computer is not actually intended to. Provide many instructions provide many addressing modes. Computer systems, computer programming, computer science book 1 introduction to the intel family of microprocessors. While performing outoforder execution, it may happen that the processor arrives at a branch for which the condition is dependent on values that are yet to be computed in preceding instructions.
Speculative execution plays a key role in the meltdown and spectre attacks. Speculative execution in high performance computer architectures. Incidentally, the purpose of the mill deferred load facility is to mask the l1 and l2 latencies, not to mask the dram latency. These modifications are layered on top of the sanctum secure processor architecture that offers strong provable isolation of software modules running concurrently and sharing resources. To me, outoforder execution is a form of speculative execution speculating that the inflight insts wont have side effects relevant to the new insts. Amazon unveils new fire hd 8 tablet with faster processor, usbc may. When they generate code, compilers take a best guess at the best order for instructions but have to err on the safe side. 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. Every single highend cpu architecture today amd, arm, ibm. 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. Ece 4750 computer architecture, fall 2019 course syllabus verilog book verilog hdl. The concept behind speculative execution is that instructions. Warter n, chang p, mahlke s, chen w and hwu w 1995 three architectural models for compilercontrolled speculative execution, ieee transactions on computers, 44.
Computer architecture books meet your next favorite book. One could design a processor this ooo but not speculative or speculative but inorder. Intel analysis of speculative execution side channels download pdf white paper. Until now, there were few textbooks that focused on the dynamic subject of speculative execution, a topic that is crucial to the development of. Chen, and jason flinn department of electrical engineering and computer science university of michigan abstract speculator provides linux kernel support for speculative execution. Were all getting quite the lesson in speculative execution today, and why faster isnt always better. Computer architecture download ebook pdf, epub, tuebl, mobi.
Branch prediction is a type of speculative execution. Speculative execution goes one step further and determines what the result would be from executing the next instructions. Emphasizing both underlying theory and actual designs, the book covers a wide array of topics and links computer architecture to other subfields of computing. Speculative execution is extensive in modern processors. Technically, ooo is the ability to move execution between different dependency chains, so skipping an inst and moving to the next one. At this stage the processor has two choices, either wait for the preceding instructions to complete and incur a huge. Speculative execution and outoforder execution are orthogonal. Speculative execution has been in the news of late, typically when. On july 9, 2019 we released security updates for the windows operating system to help mitigate this issue. 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. We define boosting, an architectural mechanism for speculative execution, that allows us to uncover. Every single highend cpu architecture today amd, arm, ibm, intel, sparc uses outoforder execution. Speculative execution arvind computer science and artificial intelligence laboratory m.
However, there has been no reference book so far that attempts to summarize and. Speculative execution article about speculative execution. Speculative execution in highperformance computer architectures. Almost none of the major computer architecture conferences in recent years can go without including some papers touched on the subject of speculative execution.
Jan 22, 2018 speculative execution plays a key role in the meltdown and spectre attacks. Ooo execution is an execution model in which instructions can be executed in an order that is potentially different from the program order. Predication and speculation department of computer. This vulnerability is a variant of the spectre variant 1 speculative execution side channel vulnerability and has been assigned cve20191125. A meltdown in computer architecture, as spectre haunts intel. Note that speculative execution can be applied even if there isnt an actual conditional branch in the code. Palnitkar prentice hall, 2003 provides a good introduction to verilog2001 well suited for the beginner. The spear speculative preexecution assisted by compiler is a further variation of the hidisc architecture. Parts of the computer and microprocessor programming fundamentals arithmetic instructions, memory accesses, control flow instructions, and data types intermediate and advanced microprocessor concepts branch prediction and speculative execution.
It covers cuttingedge research projects, as well as numerous commercial implementations that demonstrate the value of this latencyhiding technique. 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. Intel analysis of speculative execution side channels. May 14, 2019 this vulnerability is a variant of the spectre variant 1 speculative execution side channel vulnerability and has been assigned cve20191125. The concept behind speculative execution is that instructions are executed ahead of knowing that they are required.
Processor speculative execution operating system updates aws recently published aws security bulletin aws20180 for the newly disclosed research regarding sidechannel analysis via speculative execution on modern computer processors. Speculative architecture is a collaborative studio practice, led by dirk yates, that specialises in the design and delivery of public and educational buildings. Part of the lecture notes in computer science book series lncs, volume 0. Jan 04, 2018 were all getting quite the lesson in speculative execution today, and why faster isnt always better. May 16, 2019 every single highend cpu architecture today amd, arm, ibm, intel, sparc uses outoforder execution. Speculative execution is an optimization technique where a computer system performs some task that may not be needed. Another form of spec exec is branch prediction, another is walking the page tables ahead of time. Speculative execution in a distributed file system edmund b. It allows multiple processes to share speculative state. Aws recently published aws security bulletin aws20180 for the newly disclosed research regarding sidechannel analysis via speculative execution on modern computer processors. 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. From microprocessors to supercomputers provides a comprehensive introduction to this thriving and exciting field.
If the branch prediction was correct, the result is used, otherwise it is discarded. A handson approach utilizing the 80x86 microprocessor family 3rd edition computer organization and design, fourth edition. Memory address prediction for data speculation springerlink. Swarup bhunia, mark tehranipoor, in hardware security, 2019. This book examines computer architecture, computability theory, and the history of computers from the perspective of minimalist computing a framework in which the instruction set consists of a single instruction. Provides an analysis of speculative execution security risks based on sidechannel analysis methods documented by. Pipelining 387 next two stages, indicated as trace cache fetch gathers the decoded microoperations guided by branch prediction strategy from the instruction decoder and places in sequence of selection from computer architecture and organization book. Introduction 11 it deals with data path design and data ow control concepts and introduces the need of microoperations for a processor. Speculative execution in high performance computer architectures describes many recent advances in speculative execution techniques. A superscalar processor can fetch, decode, execute, and retire, e. Description structured computer organization, specifically written for undergraduate students, is a bestselling guide that provides an accessible introduction to computer hardware and architecture.
We have developed projects with institutional organisations including the queensland government, brisbane city council, museum of brisbane. 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. Computer architecture and parallel processing guide books. Ece 4750 computer architecture, fall 2019 course syllabus. 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. 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.
Well have compiler bugs for sure i write compilers but we fix them. Data speculation refers to the execution of an instruction before some logically. Sep 26, 2014 if the compiler did not hoist that code then there is a compiler bug, not an architecture problem. In general, the optimizations discussed in this chapter focus on avoiding the overhead associated with a branch.
Speculative execution in modern computer architectures. The next chapter, chapter 10, uses selection from computer architecture and organization book. And speculative execution, while implemented differently from company to company, is. By exploiting the speculative execution of modern processors, spectre attack can trick the system into executing instructions that are not supposed to. The spear speculative pre execution assisted by compiler is a further variation of the hidisc architecture. This approach is different than that taken in any other computer architecture text, and it is a bold step. This exploit, coupled with a sidechannel attack, can lead to the exposure and theft of critical secret information. Architecture of the hewlettpackards pa8200 processor. Its the oldest story in technology and perhaps in human existence. Processors can take more risks with instruction ordering when it comes to execution because, if things dont work out as planned, they can roll. Spring 2020 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.
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