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XPDS13: Xen on ARM Update - Stefano Stabellini, Citrix

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Many significant improvements have been made to Xen and Linux for the ARM architecture since September 2012, when initial support for Xen on ARM was introduced in the kernel. The number of contributors considerably increased as the number of different companies behind them. Xen on ARM has become a true multivendor project. Today Linux 3.11 can run on Xen on ARM as a DomU or Dom0, 32-bit or 64-bit, with one or more CPUs. Xen 4.3, out since July 2013, is the first hypervisor release to support ARMv7 and ARMv8 platforms. This talk will discuss the current status of the project, the principal technical advancements achieved during the last year of development and the problems still left unsolved. It will relate the experience of porting Xen to many new ARM SoCs and working with multiple hardware vendors in the ARM ecosystem, within and outside the Linaro Enterprise working Group.

Text of XPDS13: Xen on ARM Update - Stefano Stabellini, Citrix

  • 1. Xen on ARM A success storyStefano Stabellini - Citrix Xen Project Team

2. Achievements of one year Xen support for ARM upstream in Linux 3.7Xen support for ARM64 upstream in Linux 3.11Xen 64-bit on ARM64You are here 11/1108/12 09/12Part-time Xen ARM hacking starts11/12Xen running on real ARM hardwareFirst Xen on ARM talk at Xen Summit 201201/1303/13Citrix announces that will be joining Linaro06/1307/13Xen 4.3 released with ARM and ARM64 support 3. A growing community Xen-devel ARM traffic from August 2012: 4685 emails: 360 emails per month! 39% of which are not from Citrix 4. Hardware support Upstream: Versatile Express Cortex A15 Arndale board ARMv8 FVP In progress: Calxeda Midway Applied Micro Mustang Cubieboard2 Broadcom Brahma-B15 OMAP5 5. Upstream features Xen v4.3: basic lifecycle operations memory ballooning scheduler configurations and vcpu pinning Linux v3.11: dom0 and domU support 32-bit and 64-bit support SMP support PV disk, network and console 6. Coming in Xen 4.4 64-bit guest support live-migration SWIOTLB 7. Coming in Xen 4.4 64-bit guest support live-migration SWIOTLB 8. The problem1 Stagephysical addressmachine addresshardware2 stageXenLinuxvirtual address 9. The problem: dom0 DMA1 Stagephysical addressmachine addressDevice DMA2 stageXenLinuxvirtual address 10. The best solution: IOMMUMMUphysical address 2 stageLinuxvirtual addressDevice DMAIOMMUXenmachine address 11. The workaround: Dom0 1:1 mappingphysical address = machine addressXenLinuxvirtual addressDevice DMA 12. The workaround: Dom0 1:1 mapping rigid solution no ballooning in dom0 no page sharing in dom0 does not work with foreign grant table mappings 13. UNHAPPY 14. The alternative: SWIOTLBMMUvirtual addressmachine addressDevice DMADMA opsLinuxphysical address 15. The alternative: SWIOTLB use memory_exchange_and_pin hypercall create a contiguous buffer in machine memory retrieve the machine address of the buffer introduce an additional memcpy remove the need for the 1:1 workaround 16. STILL UNHAPPY 17. SWIOTLB: the improved version pin and unpin hypercalls: dynamically retrieve P2M mappings pin a mapping for DMA remove additional memcpy map_pagepfn XENMEM_pinpfnmfn pin mfn 18. SWIOTLB: the improved version Linux rbtree maintenance is expensive too many uncached address translations in Xen guest virtual to machine guest physical to machinecpu utilization increase 19. NOT AN IMPROVEMENT 20. SWIOTLB: the compromise keep the dom0 1:1 workaround dom0 without ballooning and page sharing is the default configuration in XenServer x86 today use the swiotlb only to handle DMA involving foreign grants we already know the p2m mappings of grants no need for pin and unpin hypercalls can take shortcuts: avoid many tree lookups tree lookups are much faster avoidable with IOMMU support 21. SWIOTLB: the compromise Testing platform: 1.5Ghz quad-core Cortex A15 1 Gbit link Benchmark results: same network throughput as native (line rate) < 2% cpu usage increase 22. THATS BETTER 23. SWIOTLB: where to find it The patches (swiotlb-xen v8): kernel tree: git:// swiotlb-xen-8 24. Xen 4.5+ IOMMU support in Xen device assignment UEFI booting ACPI support 25. DEMO 26. Questions?

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