Microkernel Construction Introduction Hermann Härtig SS2013 Benjamin Engel TU Dresden Operating Systems Group Microkernel Construction ClassClass GoalsGoals Provide deeper understanding of OS mechanisms Introduce L4 principles and concepts Make you become enthusiastic L4 hackers Propaganda for OS research at TU Dresden Hermann Härtig Benjamin Engel TU Dresden Operating Systems Group 2 Microkernel Construction AdministrationAdministration Thursday, 4th DS, 2 SWS Slides: http://www.tudos.org → Teaching → Microkernel Construction Subscribe to our mailing list: http://www.tudos.org/mailman/listinfo/mkc2013 In winter term: – Construction of Microkernel-based Systems (2 SWS) – Various Labs Hermann Härtig Benjamin Engel TU Dresden Operating Systems Group 3 Microkernel Construction „„Monolithic“Monolithic“ KernelKernel SystemSystem DesignDesign Application ApplicationApplication Application Unprivileged Mode Privileged File Network Mode Systems Subsystem Memory Process Drivers Management Management Monolithic Kernel Hermann Härtig Benjamin Hardware Engel TU Dresden Operating Systems Group 4 Microkernel Construction MonolithicMonolithic KernelKernel OSOS (Propaganda)(Propaganda) System components run in privileged mode ➔ No protection between system components – Faulty driver can crash the whole system – More than 2/3 of today's OS code are drivers ➔ No need for good system design – Direct access to data structures – Undocumented and frequently changing interfaces ➔ Big and inflexible – Difficult to replace system components Why something different? Hermann Härtig More and more difficult to manage increasing OS Benjamin Engel complexity TU Dresden Operating Systems Group 5 Microkernel Construction MicrokernelMicrokernel SystemSystem DesignDesign Application Application Application File Network Systems Stacks Memory Process Management Management Drivers Unprivileged System Services Mode Privileged Tasks Threads IPC Scheduling Mode Hermann Härtig Microkernel Benjamin Engel Hardware TU Dresden Operating Systems Group 6 Microkernel Construction ExampleExample –– IBMIBM WorkplaceWorkplace OSOS // MachMach OS/2 DOS OS/400 AIX Windows Application Application Application Application Application OS/2 DOS OS/400 Windows AIX Personality Personality Personality Personality Personality File Server Network Service Security Power Management Default Pager Device Support Bootstrap Name Service Hermann Mach Microkernel Härtig Benjamin Engel ARM PowerPC IA32 MIPS Alpha TU Dresden Operating Systems Group 7 Microkernel Construction ExampleExample –– QNXQNX // NeutrinoNeutrino . Embedded systems Message passing system (IPC) Network transparency Application Application Application Filesystem Device Process Network Manager Manager Manager Manager Unprivileged Mode Privileged Interrupt Network IPC Scheduler Mode Redirector Driver Hermann Härtig Neutrino - Microkernel Benjamin Engel Hardware TU Dresden Operating Systems Group 8 Microkernel Construction ExampleExample –– Fiasco.OCFiasco.OC Native Linux Native Linux L4Re Application Application Application X11 L4Linux Dope VPFS L4Re Hermann Fiasco.OC Microkernel Härtig Benjamin Engel Hardware TU Dresden Operating Systems Group 9 Microkernel Construction VisionsVisions vs.vs. RealityReality Flexibility and Customizable – Monolithic kernels are modular Maintainability and complexity – Monolithic kernel have layered architecture ✔ Robustness – Microkernels are superior due to isolated system components – Trusted code size (i386) • Fiasco kernel: about 15.000 loc • Linux kernel: about 300.000 loc (without drivers) Performance Hermann ✗ Härtig Benjamin – Application performance degraded Engel – Communication overhead (see next slides) TU Dresden Operating Systems Group 10 Microkernel Construction RobustnessRobustness vs.vs. PerformancePerformance (1)(1) System calls – Monolithic kernel: 2 kernel entries/exits – Microkernel: 4 kernel entries/exits + 2 context switches Application Application 1 4 Driver Driver 2 3 Microkernel Monolithic kernel Hermann Härtig Benjamin Engel HardwareHardware Hardware TU Dresden Operating Systems Group 11 Microkernel Construction RobustnessRobustness vs.vs. PerformancePerformance (2)(2) Calls between system services – Monolithic kernel: 1 function call – Microkernel: 4 kernel entries/exits + 2 context switches Network Network Driver Driver Subsystem Subsystem 1 4 2 3 Microkernel Monolithic kernel Hermann Härtig Benjamin Hardware Hardware Engel TU Dresden Operating Systems Group 12 Microkernel Construction ChallengesChallenges Build functional powerful and fast microkernels – Provide abstractions and mechanisms – Fast communication primitive (IPC) – Fast context switches and kernel entries/exits ➔ Subject of this lecture Build efficient OS services – Memory Management – Synchronization – Device Drivers – File Systems Hermann – Communication Interfaces Härtig Benjamin ➔ Engel Subject of lecture “Construction of Microkernel-based systems” (in winter term) TU Dresden Operating Systems Group 13 Microkernel Construction L4L4 MicrokernelMicrokernel FamilyFamily Originally developed by Jochen Liedtke (GMD / IBM Research) Current development: – Uni Karlsruhe: Pistachio – UNSW/NICTA/OKLABS: OKL4, SEL4, L4Verified – TU Dresden: Fiasco.OC, Nova Support for hardware architectures: – X86, ARM, ... Hermann Härtig Benjamin Engel TU Dresden Operating Systems Group 14 Microkernel Construction MoreMore MicrokernelsMicrokernels (Incomplete(Incomplete list)list) Commercial kernels – Singularity @ Microsoft Research – K42 @ IBM Research – velOSity/INTEGRITY @ Green Hills Software – Chorus/ChorusOS @ Sun Microsystems – PikeOS @ SYSGO AG – OKL4 Research kernels – EROS/CoyotOS @ John Hopkins University – Minix @ FU Amsterdam – Amoeba @ FU Amsterdam Hermann Härtig – Pebble @ Bell Labs Benjamin Engel – Grasshopper @ University of Sterling – Flux/Fluke @ University of Utah TU Dresden Operating Systems Group 15 Microkernel Construction L4L4 -- ConceptsConcepts Jochen Liedtke: “A microkernel does no real work” – Kernel provides only inevitable mechanisms – No policies implemented in the kernel Abstractions – Tasks with address spaces – Threads executing programs/code Mechanisms – Resource access control – Scheduling – Communication (IPC) Hermann Härtig Benjamin Engel TU Dresden Operating Systems Group 16 Microkernel Construction ThreadsThreads andand TasksTasks Task A Task B User User Code Code Thread2 User User User Stack Stack Stack Kernel Code Thread1 Thread3 Hermann Kernel Kernel Kernel Härtig Benjamin Stack Stack Stack Engel Microkernel TU Dresden Operating Systems Group 17 Microkernel Construction ThreadsThreads Represent unit of execution – Execute user code (application) – Execute kernel code (system calls, page faults, interrupts, exceptions) Subject to scheduling – Quasi-parallel execution on one CPU – Parallel execution on multiple CPUs – Voluntarily switch to another thread possible – Preemptive scheduling by the kernel according to certain parameters Associated with an address space Hermann – Executes code in one task at one point in time Härtig Benjamin • Migration allows threads move to another task Engel – Several threads can execute in one task TU Dresden Operating Systems Group 18 Microkernel Construction TasksTasks Represent domain of protection and isolation Container for code, data and resources Address space: capabilities + memory pages Three management operations: – Map: share page with other address space – Grant: give page to other address space – Unmap: revoke previously mapped page X X X grant unmap Hermann map Härtig Benjamin Engel X X X TU Dresden Operating Systems Group 19 Microkernel Construction RecursiveRecursive AddressAddress SpacesSpaces Application 1 Application 2 Pager 3 Pager 1 Pager 2 Initial Pager Hermann Härtig Benjamin Engel Physical Memory TU Dresden Operating Systems Group 20 Microkernel Construction Messages:Messages: CopyCopy DataData Direct and indirect data copy UTCB message (special area) Special case: register-only message Pagefaults during user-level memory access possible Task A Task B receive(msg, …) send(msg,…) copy data area data area Hermann data word 1 data word 1 Härtig msg data word 2 msg data word 2 Benjamin send string receive string Engel TU Dresden Operating Systems Group 21 Microkernel Construction Message:Message: MapMap ReferencesReferences Used to transfer memory pages and capabilities Kernel manipulates page tables Used to implement the map/grant operations Task A Task B send(msg,…) receive(msg, …) flexpage map flexpage Hermann send flexpage received flexpage Härtig msg msg Benjamin receive window Engel TU Dresden memory page Operating Systems Group 22 Microkernel Construction CommunicationCommunication andand ResourceResource ControlControl Need to control who can send data to whom – Security and isolation – Access to resources Approaches – IPC-redirection/introspection – Central vs. Distributed policy and mechanism – ACL-based vs. capability-based Task A Task B Thread IPC? Thread Hermann Härtig Resource Access? Benjamin Engel Hardware TU Dresden Resources Operating Systems Group 23 Microkernel Construction CapabilitiesCapabilities Task A Task B Capability Handles Capability Handles 3 1 2 1 2 2 Capability Table Capability Table C1 C3 C5C5 C1 C2 C4 Hermann Kernel Kernel Kernel Kernel Kernel Härtig Benjamin Object1 Object2 Object3 Object4 Object5 Engel TU Dresden Operating Systems Group 24 Microkernel Construction CapabilitiesCapabilities -- DetailsDetails Kernel objects represent resources and communication