PCI passthrough support

Design document
Revision	v1
Status	proposed
Review	create new issue

Introduction

GPU passthrough is already available in XAPI, this document proposes to also offer passthrough for all PCI devices through XAPI.

Design proposal

New methods for PCI object:

• PCI.enable_dom0_access
• PCI.disable_dom0_access
• PCI.get_dom0_access_status: compares the outputs of /opt/xensource/libexec/xen-cmdline and /proc/cmdline to produce one of the four values that can be currently contained in the PGPU.dom0_access field:
  • disabled
  • disabled_on_reboot
  • enabled
  • enabled_on_reboot

  How do determine the expected dom0 access state: If the device id is present in both pciback.hide of /proc/cmdline and xen-cmdline: enabled If the device id is present not in both pciback.hide of /proc/cmdline and xen-cmdline: disabled If the device id is present in the pciback.hide of /proc/cmdline but not in the one of xen-cmdline: disabled_on_reboot If the device id is not present in the pciback.hide of /proc/cmdline but is in the one of xen-cmdline: enabled_on_reboot

  A function rather than a field makes the data always accurate and even accounts for changes made by users outside XAPI, directly through /opt/xensource/libexec/xen-cmdline

With these generic methods available, the following field and methods will be deprecated:

• PGPU.enable_dom0_access
• PGPU.disable_dom0_access
• PGPU.dom0_access (DB field)

They would still be usable and up to date with the same info as for the PCI methods.

Test cases

• hide a PCI:
  • call PCI.disable_dom0_access on an enabled PCI
  • check the PCI goes in state disabled_on_reboot
  • reboot the host
  • check the PCI goes in state disabled
• unhide a PCI:
  • call PCI.enable_dom0_access on an disabled PCI
  • check the PCI goes in state enabled_on_reboot
  • reboot the host
  • check the PCI goes in state enabled
• get a PCI dom0 access state:
  • on a enabled PCI, make sure the get_dom0_access_status returns enabled
  • hide the PCI
  • make sure the get_dom0_access_status returns disabled_on_reboot
  • reboot
  • make sure the get_dom0_access_status returns disabled
  • unhide the PCI
  • make sure the get_dom0_access_status returns enabled_on_reboot
  • reboot
  • make sure the get_dom0_access_status returns enabled
• Check PCI/PGPU dom0 access coherence:
  • hide a PCI belonging to a PGPU and make sure both states remains coherent at every step
  • unhide a PCI belonging to a PGPU and make sure both states remains coherent at every step
  • hide a PGPU and make sure its and its PCI’s states remains coherent at every step
  • unhide a PGPU and make sure its and its PCI’s states remains coherent at every step