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The kvm virtualization way
KVM provides virtualization capabilities using the Linux kernel. It supports full virtualization of x86, PowerPC, s390 and IA-64 architectures using hardware extensions like Intel-VTx and AMD-V. KVM leverages existing Linux components like the scheduler and uses the Linux security model. Guests are scheduled as regular processes. Paravirtualization is used to improve performance through virtio drivers and paravirt_ops. KVM development is ongoing with goals of supporting more hardware features, improving scalability and integrating with management tools like libvirt.
In this document
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Overview of KVM virtualization presented by Amit Shah.
Discusses different virtualization strategies: native hypervisors, containers, paravirtualization, and emulation with examples.
Lists architectures supported by KVM: S390, IA-64, X86, and PowerPC with their inclusion in Linux kernel versions.
Describes 'guest mode' and hardware support for virtualization, including Intel-VTx and AMD-V.
Details kernel responsibilities including CPU and MMU virtualization, paravirtualized device support.
Explains how guests are managed within the KVM process model and how memory is mapped.
Illustrates the execution model of KVM, highlighting the transitions between user space and guest mode.
Outlines the flow of memory access when a guest accesses unmapped memory, explaining kernel traps.
Explains paravirtualisation and the use of Virtio for improving performance in virtualized environments.
Describes network device challenges and introduces Virtio-net for enhanced performance with shared memory.
Proposes ideas for improving KVM capabilities such as shared memory and VMGL support.
Lists advantages of KVM, including leveraging Linux capabilities, no guest modifications, and existing management tools.
Outlines industry interest, including distro support like Debian and RedHat, and tools like libvirt.
Describes the development philosophy aimed at frequent releases and rapid bug fixing.
Chronological overview of KVM’s development milestones from its initial release to advancements in features.
Highlights KVM’s developer-friendly aspects, including no reboot requirement and small codebase.
Discusses future enhancements for KVM, such as hardware support and improved guest scaling.
Provides references for further reading including KVM documentation and community resources.
Final thanks and acknowledgment from the presenter.
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The kvm virtualization way
- 1. KVM: Virtualisation The LinuxWay Amit Shah amit.shah@qumranet.com GEEP
- 2. Virtualisation Strategies “Native”Hypervisors Have a runtime Need a “primary” guest OS Examples: Xen, VMWare ESX Server, IBM mainframes Containers Different namespaces for different guests Run on host kernel Userland can be different from host Examples: OpenVZ, FreeVPS, Linux-Vserver Paravirtualisation Emulation Examples: QEMU, PearPC Copyright © 2007 Qumranet, Inc. All rights reserved.
- 3. KVM: Architectures Supported S390 IBM mainframes: a hypervisor is a must Included in 2.6.26 IA-64 Included in 2.6.26 X86 Included in 2.6.20 KVM-lite: PV Linux guest on non-VTx / non-SVM host (proposed) PowerPC PV Architecture support for hypervisor Included in 2.6.26 3 Copyright © 2007 Qumranet, Inc. All rights reserved.
- 4. X86 Hardware Extensions 'guest mode' in addition to user and kernel modes Raise a trap for all privileged instructions Virtualised registers Processor Intel-VTx (VMX) AMD-V (SVM) MM EPT (Intel) NPT (AMD) IO VT-d (Intel) IOMMU (AMD) Copyright © 2007 Qumranet, Inc. All rights reserved.
- 5. What's handled inthe kernel? CPU virtualisation (special instructions) MMU virtualisation Local APIC, PIC, IOAPIC, PIT (guest) paravirtualised network and block device drivers virtio-net virtio-block (guest) paravirtualised kernel support code paravirt_ops MMU (guest) paravirtualised clock driver 5 Copyright © 2007 Qumranet, Inc. All rights reserved.
- 6. KVM Process Model task task guest task task guest kernel 6 Copyright © 2007 Qumranet, Inc. All rights reserved.
- 7. KVM Process Model(cont'd) Guests are scheduled as regular processes kill(1), top(1) work as expected Guest physical memory is mapped into the task's virtual memory space Virtual processors in one VM are threads 7 Copyright © 2007 Qumranet, Inc. All rights reserved.
- 8. KVM Execution Model Userspace Kernel Guest ioctl() Switch to Guest Mode Heavyweight Lightweight Exit Native Guest Exit Execution Kernel Exit Handler Userspace Exit Handler 8 Copyright © 2007 Qumranet, Inc. All rights reserved.
- 9. Flow Example: Memory Access Guest accesses an unmapped memory location Hardware traps into kernel mode kvm walks the guest page table, determines guest physical address kvm performs guest physical -> host physical translation kvm installs shadow page table entry containing guest virtual -> host physical translation Processor restarts execution of faulting instruction 9 Copyright © 2007 Qumranet, Inc. All rights reserved.
- 10. Paravirtualisation Modifying guestOS for performance Virtio Common drivers for all hypervisors Hypervisor-specific backend KVM backend in qemu Faster performance Efficient block, net drivers Balloon lguest, KVM use it already PV DMA Pass through Ethernet devices paravirt_ops Copyright © 2007 Qumranet, Inc. All rights reserved.
- 11. Network Devices Fullyvirtualised device performance not great 55 Mbps for RTL Lots of IO-exits per packet Decided to implement a modern e1000 Advantages: All code in userspace (qemu) All existing drivers recognise device IRQ coalescing Only 2-3 IO-exits per packet Goes in excess of 800 Mbps Copyright © 2007 Qumranet, Inc. All rights reserved.
- 12. Virtio Net Sharedmemory between host and guest Two queues: recv and send Ring buffer within each queue 'available' pointer controlled by guest 'used' pointer controlled by host Copyright © 2007 Qumranet, Inc. All rights reserved.
- 13. Virtio-net on KVM BLK NET User- Virtio PCI space Guest kernel QEMU Shared Memory Linux Copyright © 2007 Qumranet, Inc. All rights reserved.
- 14. Ideas Shared memorybetween host and guest via virtio- pci Shared directory between host and guest using virtio + fuse VMGL (OpenGL for Virtual Machines) support http://kvm.qumranet.com/kvmwiki/TODO Copyright © 2007 Qumranet, Inc. All rights reserved.
- 15. KVM Pros LeveragesLinux scheduler, memory management, I/O No scheduler involvement for I/O Full virtualisation: No changes to the guest necessary Paravirt drivers available for better performance Uses existing Linux security model can run VM as ordinary user Uses existing management tools Power management Guest memory swapping Real-time scheduling, NUMA Leverages Linux development momentum: all new drivers, {cpu, disk} schedulers, file systems, etc supported Qumranet, Inc. All rights reserved. Copyright © 2007
- 16. Distro / Industryinterest libvirt Managing various guests under a hypervisor Support for Xen, KVM APIs between UI, middle layer and virtualisation backend Distributions Debian Ubuntu RedHat EL SLES Qumranet Dekstop Virtualisation Copyright © 2007 Qumranet, Inc. All rights reserved.
- 17. Release Philosophy Developmentsnapshots every 1-2 weeks Release early and often Features introduces quickly Bugs fixed quickly Bugs added quickly Allows developers and users to track and test the latest and greatest Stable releases part of Linux 2.6.x With bugfixes going into Linux 2.6.x.y Copyright © 2007 Qumranet, Inc. All rights reserved.
- 18. Journey Linux2.6.20 (4 Feb 2007): Initial release Linux 2.6.21 (25 Apr 2007): Stability, suspend/resume Linux 2.6.22 (8 Jul 2007): Stable ABI Old userspace, new kernel New userspace, old kernel Linux 2.6.23 (9 Oct 2007): SMP, performance Linux 2.6.24 (24 Jan 2008): In-kernel APIC, preemptibility, virtio Linux 2.6.25 (16 Apr 2008): Guest swapping, paravirt_ops, balloon drv Linux 2.6.26 (soon): PowerPC, s390, IA64, NPT, Copyright © 2007 Qumranet, Inc. All rights reserved. ... EPT, more paravirt (mmu),
- 19. KVM is Developer-friendly No need to reboot (usually) Netconsole, oprofile, all the tools work Small codebase Friendly community Copyright © 2007 Qumranet, Inc. All rights reserved.
- 20. Future Consolidate variousvirtualisation solutions existing in the kernel Started with move to virt/ from drivers/kvm/ More hardware features support More paravirtualisation support Improve guest scaling Better support for management layers like libvirt Intel Real Mode Emulation Copyright © 2007 Qumranet, Inc. All rights reserved.
- 21. Do Read virt/*,arch/[x86|ia64|s390|powerpc]/kvm/* KvmForum2007 wiki page on http://kvm.qumranet.com kvm@vger.kernel.org virtualization@lists.osdl.org Copyright © 2007 Qumranet, Inc. All rights reserved.
- 22.