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薛智文 cwhsueh@csie.ntu.tw csie.ntu.tw/~cwhsueh/

前瞻 資訊科技 - 虛擬化 (1) - Virtualization( V12N ). 薛智文 cwhsueh@csie.ntu.edu.tw http://www.csie.ntu.edu.tw/~cwhsueh/ 100 Fall, Oct 28, Fri 678, DTH 104. Preface. Steve Jobs (Apple, 1955-2011) Stay hunger, stay foolish. ( 求知若渴，虛心若愚。 ） Dennis Ritchie (C language, 1941-2011)

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薛智文 cwhsueh@csie.ntu.tw csie.ntu.tw/~cwhsueh/

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  1. 前瞻資訊科技 -虛擬化 (1) -Virtualization(V12N) 薛智文 cwhsueh@csie.ntu.edu.tw http://www.csie.ntu.edu.tw/~cwhsueh/ 100 Fall, Oct 28, Fri 678, DTH 104

  2. Preface • Steve Jobs (Apple, 1955-2011) • Stay hunger, stay foolish. (求知若渴，虛心若愚。） • Dennis Ritchie (Clanguage, 1941-2011) • Skype eBay (4.1B USD, 2005)  Microsoft (8.5B USD, 2011) • Linux (Linus Torvalds, 1991) • Android (Danger, 2003 Google, 2005) • Meego (Intel Samsung, Feb 2010 ) • Tizen (Intel Samsung [Nokia], Sep 2011) • Windows 8 (Microsoft, nVidia 2011) • IOS 5 (Apple, 2011) • 廣達，台積電 (2011) 持飢保愚 /37

  3. Outline • Introduction • What is virtualization? • Why is virtualization difficult? • How to virtualize? • Case Study • Inline Emulation • Domain 1 • Q&A /37

  4. What is Virtualization ? • The creation of a virtual version of something. • Virtual class • Virtual circuit • Virtual community • Virtual device • Virtual disk • Virtual host • Virtual keyboard • Virtual machine • Virtual market • Virtual memory • Virtual money • Virtual Private Network • Virtual reality • … Fully Utilizing Hardware Virtualization Etc. Sharing Hardware Resource Running Applications (x-platform) Security /37

  5. Types of Virtualization • Hardware/platform virtualization • Desktop virtualization • Software virtualization • OS-level, Workspace, Application • Storage virtualization • Data virtualization • Database virtualization • Network virtualization /37

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  7. Big Questions for Virtualization • How fast can virtualization achieve? • What kinds of applications can there be? • What problems it might incur? • Technical • Security • Business • Politics • … • Homework: • Send to TA a 3-5 page report answering any of the above or related questions. • 1-3 members per group, will be posted on course wiki. • A 5-minute talk/Q&A in the last hour of class. /37

  8. Why Virtualization is Difficult? 0/1/3 Ring, e.g. x86_32 • OS is moved to ringr1/ring3 • On x86 • Some instructions • Sensitive Instructions • Cannot be trapped OS 0/3/3 Ring, e.g. x86_64, ARM OS /37

  9. Virtual Machine Monitor (VMM)Hypervisor VM : Virtual Machine, Guest OS + Virtual Devices VM0 VM1 VMN … Hosted VMM, e.g. VMware VM0 VM1 VMN … Hypervisor, e.g. Xen Host Operating System Hardware Hardware Type I - Hypervisor Type II – Hosted VMM /37

  10. Software Execution Modes in Virtualization Environment /37

  11. The First Challenge of VirtualizationVirtualizable • According to Popek and Goldberg† in 1974, Virtual machines can be constructed for a platform if • Sensitive Instructions • might change the state of system resources • Privileged Instructions • must be executed with sufficient privilege † G. J. Popek and R. P. Goldberg, “Formal requirements for virtualizable third generation architectures,” Commun. ACM, vol. 17, no. 7, pp. 412–421, Jul. 1974. /37

  12. How to Virtualize ? • Binary translation • Hypercall Trap and emulate Full Virtualization Para Virtualization Hardware Assisted Virtualization Intel VT-x & AMD SVM /37

  13. Case Study • Inline Emulation† • Domain 1 • with Insyde Inc. † Yuan-Cheng Lee, Chih-Wen Hsueh, and Rong-Guey Chang, "Inline Emulation: An Optimization Technique for Virtualization on Embedded Systems," Proc. of the 17th International Conference on Real-Time and Embedded Computing Systems and Applications (RTCSA'11), Toyama, Japan, August 2011. /37

  14. Inline Emulation • Motivation • The First Challenge of Virtualization • Idea of Inline Emulation • Design of Inline Emulation • Evaluation and Analysis • Conclusions /37

  15. Motivation • Virtualization is fast enough on PC with 90+% performance compared to the same non-virtualized OS. • We can further utilize multi-core embedded processors • To run multiple operating systems on a mobile phone… /37

  16. Related Work • Secure Xen on ARM (Samsung) • It proved virtualization is possible for ARM platform. • The PENAR project (University of Applied Sciences, Western Switzerland) • It integrated the source trees of Xen, RTLinux, and Linux for ARM. • OKL4 (Open Kernel Labs) • A hypervisor which adopts microkernel architecture for embedded systems /37

  17. Issues on Virtualization for ARM • The most critical issue is: • Example • MOVS PC, LR // move the value in link register to PC • It will cause unpredictable behavior when executed in user mode. • SPSR: Saved Program Status Register • CPSR: Current Program Status Register Sensitive instructions Privileged instructions /37

  18. The Problematic Instructions(1/3) • Type I • Instructions which executed in user mode will cause undefined instruction (UDI) exception • We call them Canonical Privileged Instructions. • Example • MCR p15, 0, r0, c2, c0, 0 • Move r0 to c2 and c0 in coprocessor specified by p15 for operation according to option 0 and 0 Operand-dependent operation /37

  19. The Problematic Instructions(2/3) • Type II • Instructions which executed in user mode will have no effect • Example • MSR cpsr_c, #0xD3 • Switch to privileged mode and disable interrupt 31 Program Status Register (PSR) 0 Execution Flags Exception Mask Execution Mode /37

  20. The Problematic Instructions(3/3) • Type III • Instructions which executed in user mode will cause unpredictable behaviors • Example • MOVS PC, LR /37

  21. Solutions /37

  22. The First Challenge of VirtualizationExample • For the ARM architecture, the instruction (TYPE III) MOVS PC, LR • Changes the program counter and switches to user mode. • However, it causes unpredictable behavior when executed in user mode. • Therefore, it is a sensitive instruction but not a privileged instruction. Sensitive instructions Privileged instructions /37

  23. The First Challenge of VirtualizationSolutions (1/2) Dynamic Binary Translation Translation Basic Block BL TLB_FLUSH_DENTRY_NEW … TLB_FLUSH_DENTRY: MCR p15, 0, R0, C8, C6, 1 MOV PC, LR … TLB_FLUSH_DENTRY_NEW: MOV R1, R0 MOV R0, #CMD_FLUSH_DENTRY SWI #HYPER_CALL_TLB BL TLB_FLUSH_DENTRY … TLB_FLUSH_DENTRY: MCR p15, 0, R0, C8, C6, 1 MOV PC, LR … /37

  24. The First Challenge of VirtualizationSolutions (2/2) • Virtualization APIs – hypercalls /* In Hypervisor */ /* In Guest OS */ SWI Handler BL TLB_FLUSH_DENTRY … TLB_FLUSH_DENTRY: MOV R1, R0 MOV R0, #CMD_FLUSH_DENTRY SWI #HYPER_CALL_TLB … Hypercall Handler …… LDR R1, [SP, #4] MCR p15, 0, R1, C8, C6, 1 Restore User Context & PC /37

  25. Hypercall Guest OS Hypercalls No reschedule? Yes Software Interrupt context switch Hypervisor Hyper Call Handler SWI Handler /37

  26. Idea of Inline Emulation MOV R0, VIRT_ADDR MCR p15, 0, R0, C8, C6, 1 The Original Instruction Hypercall Inline Emulation Guest OS Guest OS MOV R0, VIRT_ADDR MCR p15, 0, R0, C8, C6, 1 MOV R0, #CMD_FLUSH_DENTRY MOV R1, VIRT_ADDR SWI #HYPER_CALL_TLB MCR p15, 0, R0, C8, C6, 1 Inline Emulation Handler …… Hypercall Handler …… /* restore user context */ LDMIA SP, [R0 – R14] MCR p15, 0, R0, C8, C6, 1 LDR R1, [SP, #4] MCR p15, 0, R1, C8, C6, 1 RestorePC Restore User Context & PC /37

  27. Inline Emulation Guest OS Hypercalls Canonical Privileged Instructions (TYPE I) No reschedule? Yes Software Interrupt return to guest UDI Exception context switch Hypervisor InlineEmulation Hyper Call Handler UDIHandler SWI Handler /37

  28. Design of Inline EmulationThe Main Handler A handler for the instruction is found No handler for the instruction was found /37

  29. The Issue of Finding an Inline Emulation Handler • It is hard to find a simple hash function. • Because the encoding of ARM instructions is complicated. • Instead, we can construct an efficient search table. • Because there are a few frequently used instructions. /37

  30. Example of Mto1 Search Table • Encoding of MCR instruction • Syntax: MCR{cond} cp, op1, Rd, CRn, CRm, op2 31 0 • An entry E is matched if /37

  31. Design of Inline EmulationDynamic Inline Emulation (DIE) Handler inlining the instruction flushing caches Self-modifying /37

  32. Design of Inline EmulationStatic Inline Emulation (SIE) Handler executing the hard-coded instructions /* data synchronization barrier */ restoring user context & PC /37

  33. Evaluation and AnalysisThe Experiment Environment /37

  34. Evaluation and AnalysisThe Distribution of Emulated Instructions More than 98% /37

  35. Evaluation and AnalysisThe Micro-Level Analysis (1/2) /37

  36. Evaluation and AnalysisThe Micro-Level Analysis (2/2) Inline emulation can achieve at least 4.24X performance of hypercalls in most cases (about 98%). /37

  37. Evaluation and AnalysisThe Macro-Level Analysis /37

  38. Conclusions • Inline emulation : • Reduces the efforts to port guest operating systems • Increases the handling of sensitive instructions(4-7x) • Increases the overall system performance (0.39%) • Future work • Optimization for memory virtualization • Much higher the overall speedup is possible. /37

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