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interfaces.md

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Intro

This document covers the external interfaces in a dom0less deployment that we need to document for safety certifications.

Dom0 and Xen userspace tools, such as xl and libxl, are out of scope for now, we are only discussing the hypervisor. vm_assist, xsm, argo are also out of scope: the assumption is that they will disabled via kconfig.

From the user perspective

  • Xen hypervisor command line options
  • Dom0less device tree configuration

Xen - Bootloader interfaces

  • multiboot
  • Xen boot protocol

From a DomU perspective

  • kernel image format
  • boot protocol
  • device tree
  • memory map: location of memory and other resources
  • exposed devices
    • GIC interrupt controller
    • Generic Timer
    • virtual UART (PL011)
  • PSCI
  • hypercall protocol (i.e. registers, etc.)
  • memory sharing (i.e. memory/cache attributes)

Hypercalls exposed to all DomUs

These hypercalls are unused by dom0less domUs, however, they are still exposed to all domUs.

  • memory_op
  • sched_op
  • xen_version
  • hvm_op
  • multicall
  • platform_op
  • vcpu_op
  • physdev_op (NOP on Arm)

PV drivers interfaces

Dom0less domUs cannot use PV drivers today. However, these interfaces are still exposed to them, and one day they might be able to use them correctly:

  • hypercalls
    • console_io
    • grant_table_op
    • event_channel_op
  • xenstore
    • xenstore initialization
    • xenstore protocol
      • message format
      • notifications
    • xenstore as a bus
  • PV protocols
    • PV console
    • PV network
    • PV block

Privileged hypercalls (dom0 and toolstack)

  • domctl
  • sysctl